* Re: [PATCH v21 4/8] fork: Add shadow stack support to clone3()
From: Will Deacon @ 2025-09-18 12:38 UTC (permalink / raw)
To: Mark Brown, brauner
Cc: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Shuah Khan, linux-kernel,
Catalin Marinas, jannh, Andrew Morton, Yury Khrustalev,
Wilco Dijkstra, linux-kselftest, linux-api, Kees Cook
In-Reply-To: <20250916-clone3-shadow-stack-v21-4-910493527013@kernel.org>
On Tue, Sep 16, 2025 at 12:12:09AM +0100, Mark Brown wrote:
> Unlike with the normal stack there is no API for configuring the shadow
> stack for a new thread, instead the kernel will dynamically allocate a
> new shadow stack with the same size as the normal stack. This appears to
> be due to the shadow stack series having been in development since
> before the more extensible clone3() was added rather than anything more
> deliberate.
>
> Add a parameter to clone3() specifying a shadow stack pointer to use
> for the new thread, this is inconsistent with the way we specify the
> normal stack but during review concerns were expressed about having to
> identify where the shadow stack pointer should be placed especially in
> cases where the shadow stack has been previously active. If no shadow
> stack is specified then the existing implicit allocation behaviour is
> maintained.
>
> If a shadow stack pointer is specified then it is required to have an
> architecture defined token placed on the stack, this will be consumed by
> the new task, the shadow stack is specified by pointing to this token. If
> no valid token is present then this will be reported with -EINVAL. This
> token prevents new threads being created pointing at the shadow stack of
> an existing running thread. On architectures with support for userspace
> pivoting of shadow stacks it is expected that the same format and placement
> of tokens will be used, this is the case for arm64 and x86.
>
> If the architecture does not support shadow stacks the shadow stack
> pointer must be not be specified, architectures that do support the
> feature are expected to enforce the same requirement on individual
> systems that lack shadow stack support.
>
> Update the existing arm64 and x86 implementations to pay attention to
> the newly added arguments, in order to maintain compatibility we use the
> existing behaviour if no shadow stack is specified. Since we are now
> using more fields from the kernel_clone_args we pass that into the
> shadow stack code rather than individual fields.
>
> Portions of the x86 architecture code were written by Rick Edgecombe.
>
> Acked-by: Yury Khrustalev <yury.khrustalev@arm.com>
> Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Mark Brown <broonie@kernel.org>
> ---
> arch/arm64/mm/gcs.c | 47 +++++++++++++++++++-
> arch/x86/include/asm/shstk.h | 11 +++--
> arch/x86/kernel/process.c | 2 +-
> arch/x86/kernel/shstk.c | 53 ++++++++++++++++++++---
> include/asm-generic/cacheflush.h | 11 +++++
> include/linux/sched/task.h | 17 ++++++++
> include/uapi/linux/sched.h | 9 ++--
> kernel/fork.c | 93 ++++++++++++++++++++++++++++++++++------
> 8 files changed, 217 insertions(+), 26 deletions(-)
It would be great if Christian could give this the thumbs up, given that
it changes clone3(). I think the architecture parts are all ready at this
point.
Will
^ permalink raw reply
* Re: [PATCH 00/62] initrd: remove classic initrd support
From: Andy Lutomirski @ 2025-09-17 18:00 UTC (permalink / raw)
To: Rob Landley
Cc: Askar Safin, linux-fsdevel, linux-kernel, Linus Torvalds,
Greg Kroah-Hartman, Christian Brauner, Al Viro, Jan Kara,
Christoph Hellwig, Jens Axboe, Andy Shevchenko, Aleksa Sarai,
Thomas Weißschuh, Julian Stecklina, Gao Xiang, Art Nikpal,
Andrew Morton, Eric Curtin, Alexander Graf, Lennart Poettering,
linux-arch, linux-alpha, linux-snps-arc, linux-arm-kernel,
linux-csky, linux-hexagon, loongarch, linux-m68k, linux-mips,
linux-openrisc, linux-parisc, linuxppc-dev, linux-riscv,
linux-s390, linux-sh, sparclinux, linux-um, x86, Ingo Molnar,
linux-block, initramfs, linux-api, linux-doc, linux-efi,
linux-ext4, Theodore Y . Ts'o, linux-acpi, Michal Simek,
devicetree, Luis Chamberlain, Kees Cook, Thorsten Blum,
Heiko Carstens, patches
In-Reply-To: <0342fbda-9901-4293-afa7-ba6085eb1688@landley.net>
On Mon, Sep 15, 2025 at 10:09 AM Rob Landley <rob@landley.net> wrote:
> While you're at it, could you fix static/builtin initramfs so PID 1 has
> a valid stdin/stdout/stderr?
>
> A static initramfs won't create /dev/console if the embedded initramfs
> image doesn't contain it, which a non-root build can't mknod, so the
> kernel plumbing won't see it dev in the directory we point it at unless
> we build with root access.
I have no current insight as to whether there's a kernel issue here,
but why are you trying to put actual device nodes in an actual
filesystem as part of a build process? It's extremely straightforward
to emit devices nodes in cpio format, and IMO it's far *more*
straightforward to do that than to make a whole directory, try to get
all the modes right, and cpio it up.
I wrote an absolutely trivial tool for this several years ago:
https://github.com/amluto/virtme/blob/master/virtme/cpiowriter.py
it would be barely more complicated to strip the trailer off an cpio
file from some other source, add some device nodes, and stick the
trailer back on. But it's also really, really, really easy to emit an
entire, functioning cpio-formatted initramfs from plain user code with
no filesystem manipulation at all. This also makes that portion of
the build reproducible, which is worth quite a bit IMO.
--Andy
^ permalink raw reply
* Re: [PATCH v2 3/3] ext4: implemet new ioctls to set and get superblock parameters
From: Jan Kara @ 2025-09-17 16:22 UTC (permalink / raw)
To: tytso; +Cc: linux-ext4, linux-api
In-Reply-To: <20250916-tune2fs-v2-3-d594dc7486f0@mit.edu>
On Tue 16-09-25 23:22:49, Theodore Ts'o via B4 Relay wrote:
> From: Theodore Ts'o <tytso@mit.edu>
>
> Implement the EXT4_IOC_GET_TUNE_SB_PARAM and
> EXT4_IOC_SET_TUNE_SB_PARAM ioctls, which allow certains superblock
> parameters to be set while the file system is mounted, without needing
> write access to the block device.
>
> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Looks good. Feel free to add:
Reviewed-by: Jan Kara <jack@suse.cz>
Honza
> ---
> fs/ext4/ioctl.c | 312 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
> include/uapi/linux/ext4.h | 53 +++++++++++++
> 2 files changed, 358 insertions(+), 7 deletions(-)
>
> diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
> index 84e3c73952d72e436429489f5fc8b7ae1c01c7a1..a93a7baae990cc5580d2ddb3ffcc72fe15246978 100644
> --- a/fs/ext4/ioctl.c
> +++ b/fs/ext4/ioctl.c
> @@ -27,14 +27,16 @@
> #include "fsmap.h"
> #include <trace/events/ext4.h>
>
> -typedef void ext4_update_sb_callback(struct ext4_super_block *es,
> - const void *arg);
> +typedef void ext4_update_sb_callback(struct ext4_sb_info *sbi,
> + struct ext4_super_block *es,
> + const void *arg);
>
> /*
> * Superblock modification callback function for changing file system
> * label
> */
> -static void ext4_sb_setlabel(struct ext4_super_block *es, const void *arg)
> +static void ext4_sb_setlabel(struct ext4_sb_info *sbi,
> + struct ext4_super_block *es, const void *arg)
> {
> /* Sanity check, this should never happen */
> BUILD_BUG_ON(sizeof(es->s_volume_name) < EXT4_LABEL_MAX);
> @@ -46,7 +48,8 @@ static void ext4_sb_setlabel(struct ext4_super_block *es, const void *arg)
> * Superblock modification callback function for changing file system
> * UUID.
> */
> -static void ext4_sb_setuuid(struct ext4_super_block *es, const void *arg)
> +static void ext4_sb_setuuid(struct ext4_sb_info *sbi,
> + struct ext4_super_block *es, const void *arg)
> {
> memcpy(es->s_uuid, (__u8 *)arg, UUID_SIZE);
> }
> @@ -71,7 +74,7 @@ int ext4_update_primary_sb(struct super_block *sb, handle_t *handle,
> goto out_err;
>
> lock_buffer(bh);
> - func(es, arg);
> + func(sbi, es, arg);
> ext4_superblock_csum_set(sb);
> unlock_buffer(bh);
>
> @@ -149,7 +152,7 @@ static int ext4_update_backup_sb(struct super_block *sb,
> unlock_buffer(bh);
> goto out_bh;
> }
> - func(es, arg);
> + func(EXT4_SB(sb), es, arg);
> if (ext4_has_feature_metadata_csum(sb))
> es->s_checksum = ext4_superblock_csum(es);
> set_buffer_uptodate(bh);
> @@ -1230,6 +1233,295 @@ static int ext4_ioctl_setuuid(struct file *filp,
> return ret;
> }
>
> +
> +#define TUNE_OPS_SUPPORTED (EXT4_TUNE_FL_ERRORS_BEHAVIOR | \
> + EXT4_TUNE_FL_MNT_COUNT | EXT4_TUNE_FL_MAX_MNT_COUNT | \
> + EXT4_TUNE_FL_CHECKINTRVAL | EXT4_TUNE_FL_LAST_CHECK_TIME | \
> + EXT4_TUNE_FL_RESERVED_BLOCKS | EXT4_TUNE_FL_RESERVED_UID | \
> + EXT4_TUNE_FL_RESERVED_GID | EXT4_TUNE_FL_DEFAULT_MNT_OPTS | \
> + EXT4_TUNE_FL_DEF_HASH_ALG | EXT4_TUNE_FL_RAID_STRIDE | \
> + EXT4_TUNE_FL_RAID_STRIPE_WIDTH | EXT4_TUNE_FL_MOUNT_OPTS | \
> + EXT4_TUNE_FL_FEATURES | EXT4_TUNE_FL_EDIT_FEATURES | \
> + EXT4_TUNE_FL_FORCE_FSCK | EXT4_TUNE_FL_ENCODING | \
> + EXT4_TUNE_FL_ENCODING_FLAGS)
> +
> +#define EXT4_TUNE_SET_COMPAT_SUPP \
> + (EXT4_FEATURE_COMPAT_DIR_INDEX | \
> + EXT4_FEATURE_COMPAT_STABLE_INODES)
> +#define EXT4_TUNE_SET_INCOMPAT_SUPP \
> + (EXT4_FEATURE_INCOMPAT_EXTENTS | \
> + EXT4_FEATURE_INCOMPAT_EA_INODE | \
> + EXT4_FEATURE_INCOMPAT_ENCRYPT | \
> + EXT4_FEATURE_INCOMPAT_CSUM_SEED | \
> + EXT4_FEATURE_INCOMPAT_LARGEDIR | \
> + EXT4_FEATURE_INCOMPAT_CASEFOLD)
> +#define EXT4_TUNE_SET_RO_COMPAT_SUPP \
> + (EXT4_FEATURE_RO_COMPAT_LARGE_FILE | \
> + EXT4_FEATURE_RO_COMPAT_DIR_NLINK | \
> + EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE | \
> + EXT4_FEATURE_RO_COMPAT_PROJECT | \
> + EXT4_FEATURE_RO_COMPAT_VERITY)
> +
> +#define EXT4_TUNE_CLEAR_COMPAT_SUPP (0)
> +#define EXT4_TUNE_CLEAR_INCOMPAT_SUPP (0)
> +#define EXT4_TUNE_CLEAR_RO_COMPAT_SUPP (0)
> +
> +#define SB_ENC_SUPP_MASK (SB_ENC_STRICT_MODE_FL | \
> + SB_ENC_NO_COMPAT_FALLBACK_FL)
> +
> +static int ext4_ioctl_get_tune_sb(struct ext4_sb_info *sbi,
> + struct ext4_tune_sb_params __user *params)
> +{
> + struct ext4_tune_sb_params ret;
> + struct ext4_super_block *es = sbi->s_es;
> +
> + memset(&ret, 0, sizeof(ret));
> + ret.set_flags = TUNE_OPS_SUPPORTED;
> + ret.errors_behavior = le16_to_cpu(es->s_errors);
> + ret.mnt_count = le16_to_cpu(es->s_mnt_count);
> + ret.max_mnt_count = le16_to_cpu(es->s_max_mnt_count);
> + ret.checkinterval = le32_to_cpu(es->s_checkinterval);
> + ret.last_check_time = le32_to_cpu(es->s_lastcheck);
> + ret.reserved_blocks = ext4_r_blocks_count(es);
> + ret.blocks_count = ext4_blocks_count(es);
> + ret.reserved_uid = ext4_get_resuid(es);
> + ret.reserved_gid = ext4_get_resgid(es);
> + ret.default_mnt_opts = le32_to_cpu(es->s_default_mount_opts);
> + ret.def_hash_alg = es->s_def_hash_version;
> + ret.raid_stride = le16_to_cpu(es->s_raid_stride);
> + ret.raid_stripe_width = le32_to_cpu(es->s_raid_stripe_width);
> + ret.encoding = le16_to_cpu(es->s_encoding);
> + ret.encoding_flags = le16_to_cpu(es->s_encoding_flags);
> + strscpy_pad(ret.mount_opts, es->s_mount_opts);
> + ret.feature_compat = le32_to_cpu(es->s_feature_compat);
> + ret.feature_incompat = le32_to_cpu(es->s_feature_incompat);
> + ret.feature_ro_compat = le32_to_cpu(es->s_feature_ro_compat);
> + ret.set_feature_compat_mask = EXT4_TUNE_SET_COMPAT_SUPP;
> + ret.set_feature_incompat_mask = EXT4_TUNE_SET_INCOMPAT_SUPP;
> + ret.set_feature_ro_compat_mask = EXT4_TUNE_SET_RO_COMPAT_SUPP;
> + ret.clear_feature_compat_mask = EXT4_TUNE_CLEAR_COMPAT_SUPP;
> + ret.clear_feature_incompat_mask = EXT4_TUNE_CLEAR_INCOMPAT_SUPP;
> + ret.clear_feature_ro_compat_mask = EXT4_TUNE_CLEAR_RO_COMPAT_SUPP;
> + if (copy_to_user(params, &ret, sizeof(ret)))
> + return -EFAULT;
> + return 0;
> +}
> +
> +static void ext4_sb_setparams(struct ext4_sb_info *sbi,
> + struct ext4_super_block *es, const void *arg)
> +{
> + const struct ext4_tune_sb_params *params = arg;
> +
> + if (params->set_flags & EXT4_TUNE_FL_ERRORS_BEHAVIOR)
> + es->s_errors = cpu_to_le16(params->errors_behavior);
> + if (params->set_flags & EXT4_TUNE_FL_MNT_COUNT)
> + es->s_mnt_count = cpu_to_le16(params->mnt_count);
> + if (params->set_flags & EXT4_TUNE_FL_MAX_MNT_COUNT)
> + es->s_max_mnt_count = cpu_to_le16(params->max_mnt_count);
> + if (params->set_flags & EXT4_TUNE_FL_CHECKINTRVAL)
> + es->s_checkinterval = cpu_to_le32(params->checkinterval);
> + if (params->set_flags & EXT4_TUNE_FL_LAST_CHECK_TIME)
> + es->s_lastcheck = cpu_to_le32(params->last_check_time);
> + if (params->set_flags & EXT4_TUNE_FL_RESERVED_BLOCKS) {
> + ext4_fsblk_t blk = params->reserved_blocks;
> +
> + es->s_r_blocks_count_lo = cpu_to_le32((u32)blk);
> + es->s_r_blocks_count_hi = cpu_to_le32(blk >> 32);
> + }
> + if (params->set_flags & EXT4_TUNE_FL_RESERVED_UID) {
> + int uid = params->reserved_uid;
> +
> + es->s_def_resuid = cpu_to_le16(uid & 0xFFFF);
> + es->s_def_resuid_hi = cpu_to_le16(uid >> 16);
> + }
> + if (params->set_flags & EXT4_TUNE_FL_RESERVED_GID) {
> + int gid = params->reserved_gid;
> +
> + es->s_def_resgid = cpu_to_le16(gid & 0xFFFF);
> + es->s_def_resgid_hi = cpu_to_le16(gid >> 16);
> + }
> + if (params->set_flags & EXT4_TUNE_FL_DEFAULT_MNT_OPTS)
> + es->s_default_mount_opts = cpu_to_le32(params->default_mnt_opts);
> + if (params->set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
> + es->s_def_hash_version = params->def_hash_alg;
> + if (params->set_flags & EXT4_TUNE_FL_RAID_STRIDE)
> + es->s_raid_stride = cpu_to_le16(params->raid_stride);
> + if (params->set_flags & EXT4_TUNE_FL_RAID_STRIPE_WIDTH)
> + es->s_raid_stripe_width =
> + cpu_to_le32(params->raid_stripe_width);
> + if (params->set_flags & EXT4_TUNE_FL_ENCODING)
> + es->s_encoding = cpu_to_le16(params->encoding);
> + if (params->set_flags & EXT4_TUNE_FL_ENCODING_FLAGS)
> + es->s_encoding_flags = cpu_to_le16(params->encoding_flags);
> + strscpy_pad(es->s_mount_opts, params->mount_opts);
> + if (params->set_flags & EXT4_TUNE_FL_EDIT_FEATURES) {
> + es->s_feature_compat |=
> + cpu_to_le32(params->set_feature_compat_mask);
> + es->s_feature_incompat |=
> + cpu_to_le32(params->set_feature_incompat_mask);
> + es->s_feature_ro_compat |=
> + cpu_to_le32(params->set_feature_ro_compat_mask);
> + es->s_feature_compat &=
> + ~cpu_to_le32(params->clear_feature_compat_mask);
> + es->s_feature_incompat &=
> + ~cpu_to_le32(params->clear_feature_incompat_mask);
> + es->s_feature_ro_compat &=
> + ~cpu_to_le32(params->clear_feature_ro_compat_mask);
> + if (params->set_feature_compat_mask &
> + EXT4_FEATURE_COMPAT_DIR_INDEX)
> + es->s_def_hash_version = sbi->s_def_hash_version;
> + if (params->set_feature_incompat_mask &
> + EXT4_FEATURE_INCOMPAT_CSUM_SEED)
> + es->s_checksum_seed = cpu_to_le32(sbi->s_csum_seed);
> + }
> + if (params->set_flags & EXT4_TUNE_FL_FORCE_FSCK)
> + es->s_state |= cpu_to_le16(EXT4_ERROR_FS);
> +}
> +
> +static int ext4_ioctl_set_tune_sb(struct file *filp,
> + struct ext4_tune_sb_params __user *in)
> +{
> + struct ext4_tune_sb_params params;
> + struct super_block *sb = file_inode(filp)->i_sb;
> + struct ext4_sb_info *sbi = EXT4_SB(sb);
> + struct ext4_super_block *es = sbi->s_es;
> + int enabling_casefold = 0;
> + int ret;
> +
> + if (!capable(CAP_SYS_ADMIN))
> + return -EPERM;
> +
> + if (copy_from_user(¶ms, in, sizeof(params)))
> + return -EFAULT;
> +
> + if ((params.set_flags & ~TUNE_OPS_SUPPORTED) != 0)
> + return -EOPNOTSUPP;
> +
> + if ((params.set_flags & EXT4_TUNE_FL_ERRORS_BEHAVIOR) &&
> + (params.errors_behavior > EXT4_ERRORS_PANIC))
> + return -EINVAL;
> +
> + if ((params.set_flags & EXT4_TUNE_FL_RESERVED_BLOCKS) &&
> + (params.reserved_blocks > ext4_blocks_count(sbi->s_es) / 2))
> + return -EINVAL;
> + if ((params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG) &&
> + ((params.def_hash_alg > DX_HASH_LAST) ||
> + (params.def_hash_alg == DX_HASH_SIPHASH)))
> + return -EINVAL;
> + if ((params.set_flags & EXT4_TUNE_FL_FEATURES) &&
> + (params.set_flags & EXT4_TUNE_FL_EDIT_FEATURES))
> + return -EINVAL;
> +
> + if (params.set_flags & EXT4_TUNE_FL_FEATURES) {
> + params.set_feature_compat_mask =
> + params.feature_compat &
> + ~le32_to_cpu(es->s_feature_compat);
> + params.set_feature_incompat_mask =
> + params.feature_incompat &
> + ~le32_to_cpu(es->s_feature_incompat);
> + params.set_feature_ro_compat_mask =
> + params.feature_ro_compat &
> + ~le32_to_cpu(es->s_feature_ro_compat);
> + params.clear_feature_compat_mask =
> + ~params.feature_compat &
> + le32_to_cpu(es->s_feature_compat);
> + params.clear_feature_incompat_mask =
> + ~params.feature_incompat &
> + le32_to_cpu(es->s_feature_incompat);
> + params.clear_feature_ro_compat_mask =
> + ~params.feature_ro_compat &
> + le32_to_cpu(es->s_feature_ro_compat);
> + params.set_flags |= EXT4_TUNE_FL_EDIT_FEATURES;
> + }
> + if (params.set_flags & EXT4_TUNE_FL_EDIT_FEATURES) {
> + if ((params.set_feature_compat_mask &
> + ~EXT4_TUNE_SET_COMPAT_SUPP) ||
> + (params.set_feature_incompat_mask &
> + ~EXT4_TUNE_SET_INCOMPAT_SUPP) ||
> + (params.set_feature_ro_compat_mask &
> + ~EXT4_TUNE_SET_RO_COMPAT_SUPP) ||
> + (params.clear_feature_compat_mask &
> + ~EXT4_TUNE_CLEAR_COMPAT_SUPP) ||
> + (params.clear_feature_incompat_mask &
> + ~EXT4_TUNE_CLEAR_INCOMPAT_SUPP) ||
> + (params.clear_feature_ro_compat_mask &
> + ~EXT4_TUNE_CLEAR_RO_COMPAT_SUPP))
> + return -EOPNOTSUPP;
> +
> + /*
> + * Filter out the features that are already set from
> + * the set_mask.
> + */
> + params.set_feature_compat_mask &=
> + ~le32_to_cpu(es->s_feature_compat);
> + params.set_feature_incompat_mask &=
> + ~le32_to_cpu(es->s_feature_incompat);
> + params.set_feature_ro_compat_mask &=
> + ~le32_to_cpu(es->s_feature_ro_compat);
> + if ((params.set_feature_incompat_mask &
> + EXT4_FEATURE_INCOMPAT_CASEFOLD)) {
> + enabling_casefold = 1;
> + if (!(params.set_flags & EXT4_TUNE_FL_ENCODING)) {
> + params.encoding = EXT4_ENC_UTF8_12_1;
> + params.set_flags |= EXT4_TUNE_FL_ENCODING;
> + }
> + if (!(params.set_flags & EXT4_TUNE_FL_ENCODING_FLAGS)) {
> + params.encoding_flags = 0;
> + params.set_flags |= EXT4_TUNE_FL_ENCODING_FLAGS;
> + }
> + }
> + if ((params.set_feature_compat_mask &
> + EXT4_FEATURE_COMPAT_DIR_INDEX)) {
> + uuid_t uu;
> +
> + memcpy(&uu, sbi->s_hash_seed, UUID_SIZE);
> + if (uuid_is_null(&uu))
> + generate_random_uuid((char *)
> + &sbi->s_hash_seed);
> + if (params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
> + sbi->s_def_hash_version = params.def_hash_alg;
> + else if (sbi->s_def_hash_version == 0)
> + sbi->s_def_hash_version = DX_HASH_HALF_MD4;
> + if (!(es->s_flags &
> + cpu_to_le32(EXT2_FLAGS_UNSIGNED_HASH)) &&
> + !(es->s_flags &
> + cpu_to_le32(EXT2_FLAGS_SIGNED_HASH))) {
> +#ifdef __CHAR_UNSIGNED__
> + sbi->s_hash_unsigned = 3;
> +#else
> + sbi->s_hash_unsigned = 0;
> +#endif
> + }
> + }
> + }
> + if (params.set_flags & EXT4_TUNE_FL_ENCODING) {
> + if (!enabling_casefold)
> + return -EINVAL;
> + if (params.encoding == 0)
> + params.encoding = EXT4_ENC_UTF8_12_1;
> + else if (params.encoding != EXT4_ENC_UTF8_12_1)
> + return -EINVAL;
> + }
> + if (params.set_flags & EXT4_TUNE_FL_ENCODING_FLAGS) {
> + if (!enabling_casefold)
> + return -EINVAL;
> + if (params.encoding_flags & ~SB_ENC_SUPP_MASK)
> + return -EINVAL;
> + }
> +
> + ret = mnt_want_write_file(filp);
> + if (ret)
> + return ret;
> +
> + ret = ext4_update_superblocks_fn(sb, ext4_sb_setparams, ¶ms);
> + mnt_drop_write_file(filp);
> +
> + if (params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
> + sbi->s_def_hash_version = params.def_hash_alg;
> +
> + return ret;
> +}
> +
> static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> {
> struct inode *inode = file_inode(filp);
> @@ -1616,6 +1908,11 @@ static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> return ext4_ioctl_getuuid(EXT4_SB(sb), (void __user *)arg);
> case EXT4_IOC_SETFSUUID:
> return ext4_ioctl_setuuid(filp, (const void __user *)arg);
> + case EXT4_IOC_GET_TUNE_SB_PARAM:
> + return ext4_ioctl_get_tune_sb(EXT4_SB(sb),
> + (void __user *)arg);
> + case EXT4_IOC_SET_TUNE_SB_PARAM:
> + return ext4_ioctl_set_tune_sb(filp, (void __user *)arg);
> default:
> return -ENOTTY;
> }
> @@ -1703,7 +2000,8 @@ long ext4_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> }
> #endif
>
> -static void set_overhead(struct ext4_super_block *es, const void *arg)
> +static void set_overhead(struct ext4_sb_info *sbi,
> + struct ext4_super_block *es, const void *arg)
> {
> es->s_overhead_clusters = cpu_to_le32(*((unsigned long *) arg));
> }
> diff --git a/include/uapi/linux/ext4.h b/include/uapi/linux/ext4.h
> index 1c4c2dd29112cda9f7dc91d917492cffc33ee524..411dcc1e4a35c8c6a10f3768d17b8cc50cff4c34 100644
> --- a/include/uapi/linux/ext4.h
> +++ b/include/uapi/linux/ext4.h
> @@ -33,6 +33,8 @@
> #define EXT4_IOC_CHECKPOINT _IOW('f', 43, __u32)
> #define EXT4_IOC_GETFSUUID _IOR('f', 44, struct fsuuid)
> #define EXT4_IOC_SETFSUUID _IOW('f', 44, struct fsuuid)
> +#define EXT4_IOC_GET_TUNE_SB_PARAM _IOR('f', 45, struct ext4_tune_sb_params)
> +#define EXT4_IOC_SET_TUNE_SB_PARAM _IOW('f', 46, struct ext4_tune_sb_params)
>
> #define EXT4_IOC_SHUTDOWN _IOR('X', 125, __u32)
>
> @@ -108,6 +110,57 @@ struct ext4_new_group_input {
> __u16 unused;
> };
>
> +struct ext4_tune_sb_params {
> + __u32 set_flags;
> + __u32 checkinterval;
> + __u16 errors_behavior;
> + __u16 mnt_count;
> + __u16 max_mnt_count;
> + __u16 raid_stride;
> + __u64 last_check_time;
> + __u64 reserved_blocks;
> + __u64 blocks_count;
> + __u32 default_mnt_opts;
> + __u32 reserved_uid;
> + __u32 reserved_gid;
> + __u32 raid_stripe_width;
> + __u16 encoding;
> + __u16 encoding_flags;
> + __u8 def_hash_alg;
> + __u8 pad_1;
> + __u16 pad_2;
> + __u32 feature_compat;
> + __u32 feature_incompat;
> + __u32 feature_ro_compat;
> + __u32 set_feature_compat_mask;
> + __u32 set_feature_incompat_mask;
> + __u32 set_feature_ro_compat_mask;
> + __u32 clear_feature_compat_mask;
> + __u32 clear_feature_incompat_mask;
> + __u32 clear_feature_ro_compat_mask;
> + __u8 mount_opts[64];
> + __u8 pad[64];
> +};
> +
> +#define EXT4_TUNE_FL_ERRORS_BEHAVIOR 0x00000001
> +#define EXT4_TUNE_FL_MNT_COUNT 0x00000002
> +#define EXT4_TUNE_FL_MAX_MNT_COUNT 0x00000004
> +#define EXT4_TUNE_FL_CHECKINTRVAL 0x00000008
> +#define EXT4_TUNE_FL_LAST_CHECK_TIME 0x00000010
> +#define EXT4_TUNE_FL_RESERVED_BLOCKS 0x00000020
> +#define EXT4_TUNE_FL_RESERVED_UID 0x00000040
> +#define EXT4_TUNE_FL_RESERVED_GID 0x00000080
> +#define EXT4_TUNE_FL_DEFAULT_MNT_OPTS 0x00000100
> +#define EXT4_TUNE_FL_DEF_HASH_ALG 0x00000200
> +#define EXT4_TUNE_FL_RAID_STRIDE 0x00000400
> +#define EXT4_TUNE_FL_RAID_STRIPE_WIDTH 0x00000800
> +#define EXT4_TUNE_FL_MOUNT_OPTS 0x00001000
> +#define EXT4_TUNE_FL_FEATURES 0x00002000
> +#define EXT4_TUNE_FL_EDIT_FEATURES 0x00004000
> +#define EXT4_TUNE_FL_FORCE_FSCK 0x00008000
> +#define EXT4_TUNE_FL_ENCODING 0x00010000
> +#define EXT4_TUNE_FL_ENCODING_FLAGS 0x00020000
> +
> /*
> * Returned by EXT4_IOC_GET_ES_CACHE as an additional possible flag.
> * It indicates that the entry in extent status cache is for a hole.
>
> --
> 2.51.0
>
>
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
^ permalink raw reply
* Re: [PATCH v2 2/3] ext4: add support for 32-bit default reserved uid and gid values
From: Jan Kara @ 2025-09-17 16:10 UTC (permalink / raw)
To: tytso; +Cc: linux-ext4, linux-api
In-Reply-To: <20250916-tune2fs-v2-2-d594dc7486f0@mit.edu>
On Tue 16-09-25 23:22:48, Theodore Ts'o via B4 Relay wrote:
> From: Theodore Ts'o <tytso@mit.edu>
>
> Support for specifying the default user id and group id that is
> allowed to use the reserved block space was added way back when Linux
> only supported 16-bit uid's and gid's. (Yeah, that long ago.) It's
> not a commonly used feature, but let's add support for 32-bit user and
> group id's.
>
> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
> ---
> fs/ext4/ext4.h | 16 +++++++++++++++-
> fs/ext4/super.c | 8 ++++----
> 2 files changed, 19 insertions(+), 5 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 01a6e2de7fc3ef0e20b039d3200b9c9bd656f59f..4bfcd5f0c74fda30db4009ee28fbee00a2f6b76f 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1442,7 +1442,9 @@ struct ext4_super_block {
> __le16 s_encoding; /* Filename charset encoding */
> __le16 s_encoding_flags; /* Filename charset encoding flags */
> __le32 s_orphan_file_inum; /* Inode for tracking orphan inodes */
> - __le32 s_reserved[94]; /* Padding to the end of the block */
> + __le16 s_def_resuid_hi;
> + __le16 s_def_resgid_hi;
> + __le32 s_reserved[93]; /* Padding to the end of the block */
> __le32 s_checksum; /* crc32c(superblock) */
> };
>
> @@ -1812,6 +1814,18 @@ static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino)
> ino <= le32_to_cpu(EXT4_SB(sb)->s_es->s_inodes_count));
> }
>
> +static inline int ext4_get_resuid(struct ext4_super_block *es)
> +{
> + return(le16_to_cpu(es->s_def_resuid) |
> + (le16_to_cpu(es->s_def_resuid_hi) << 16));
> +}
I'd prefer a style like:
return le16_to_cpu(es->s_def_resuid) |
(le16_to_cpu(es->s_def_resuid_hi) << 16);
but whatever...
> @@ -5270,8 +5270,8 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
>
> ext4_set_def_opts(sb, es);
>
> - sbi->s_resuid = make_kuid(&init_user_ns, le16_to_cpu(es->s_def_resuid));
> - sbi->s_resgid = make_kgid(&init_user_ns, le16_to_cpu(es->s_def_resgid));
> + sbi->s_resuid = make_kuid(&init_user_ns, ext4_get_resuid(es));
> + sbi->s_resgid = make_kgid(&init_user_ns, ext4_get_resuid(es));
^^^^ ext4_get_resgid() here.
> sbi->s_commit_interval = JBD2_DEFAULT_MAX_COMMIT_AGE * HZ;
> sbi->s_min_batch_time = EXT4_DEF_MIN_BATCH_TIME;
> sbi->s_max_batch_time = EXT4_DEF_MAX_BATCH_TIME;
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
^ permalink raw reply
* Re: [PATCH v2 1/3] ext4: avoid potential buffer over-read in parse_apply_sb_mount_options()
From: Jan Kara @ 2025-09-17 16:05 UTC (permalink / raw)
To: tytso; +Cc: linux-ext4, linux-api, stable
In-Reply-To: <20250916-tune2fs-v2-1-d594dc7486f0@mit.edu>
On Tue 16-09-25 23:22:47, Theodore Ts'o via B4 Relay wrote:
> From: Theodore Ts'o <tytso@mit.edu>
>
> Unlike other strings in the ext4 superblock, we rely on tune2fs to
> make sure s_mount_opts is NUL terminated. Harden
> parse_apply_sb_mount_options() by treating s_mount_opts as a potential
> __nonstring.
>
> Cc: stable@vger.kernel.org
> Fixes: 8b67f04ab9de ("ext4: Add mount options in superblock")
> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Looks good. Feel free to add:
Reviewed-by: Jan Kara <jack@suse.cz>
Honza
> ---
> fs/ext4/super.c | 17 +++++------------
> 1 file changed, 5 insertions(+), 12 deletions(-)
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 699c15db28a82f26809bf68533454a242596f0fd..94c98446c84f9a4614971d246ca7f001de610a8a 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -2460,7 +2460,7 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
> struct ext4_fs_context *m_ctx)
> {
> struct ext4_sb_info *sbi = EXT4_SB(sb);
> - char *s_mount_opts = NULL;
> + char s_mount_opts[65];
> struct ext4_fs_context *s_ctx = NULL;
> struct fs_context *fc = NULL;
> int ret = -ENOMEM;
> @@ -2468,15 +2468,11 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
> if (!sbi->s_es->s_mount_opts[0])
> return 0;
>
> - s_mount_opts = kstrndup(sbi->s_es->s_mount_opts,
> - sizeof(sbi->s_es->s_mount_opts),
> - GFP_KERNEL);
> - if (!s_mount_opts)
> - return ret;
> + strscpy_pad(s_mount_opts, sbi->s_es->s_mount_opts);
>
> fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL);
> if (!fc)
> - goto out_free;
> + return -ENOMEM;
>
> s_ctx = kzalloc(sizeof(struct ext4_fs_context), GFP_KERNEL);
> if (!s_ctx)
> @@ -2508,11 +2504,8 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
> ret = 0;
>
> out_free:
> - if (fc) {
> - ext4_fc_free(fc);
> - kfree(fc);
> - }
> - kfree(s_mount_opts);
> + ext4_fc_free(fc);
> + kfree(fc);
> return ret;
> }
>
>
> --
> 2.51.0
>
>
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
^ permalink raw reply
* [PATCH v2 0/3] ext4: Add support for mounted updates to the superblock via an ioctl
From: Theodore Ts'o via B4 Relay @ 2025-09-17 3:22 UTC (permalink / raw)
To: tytso; +Cc: linux-ext4, linux-api, stable
This patch series enables a future version of tune2fs to be able to
modify certain parts of the ext4 superblock without to write to the
block device.
The first patch fixes a potential buffer overrun caused by a
maliciously moified superblock. The second patch adds support for
32-bit uid and gid's which can have access to the reserved blocks pool.
The last patch adds the ioctl's which will be used by tune2fs.
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
Changes in v2:
- fix bugs that were detected using sparse
- remove tune (unsafe) ability to clear certain compat faatures
- add the ability to set the encoding and encoding flags for case folding
- Link to v1: https://lore.kernel.org/r/20250908-tune2fs-v1-0-e3a6929f3355@mit.edu
---
Theodore Ts'o (3):
ext4: avoid potential buffer over-read in parse_apply_sb_mount_options()
ext4: add support for 32-bit default reserved uid and gid values
ext4: implemet new ioctls to set and get superblock parameters
fs/ext4/ext4.h | 16 +++-
fs/ext4/ioctl.c | 312 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
fs/ext4/super.c | 25 +++----
include/uapi/linux/ext4.h | 53 +++++++++++++
4 files changed, 382 insertions(+), 24 deletions(-)
---
base-commit: b320789d6883cc00ac78ce83bccbfe7ed58afcf0
change-id: 20250830-tune2fs-3376beb72403
Best regards,
--
Theodore Ts'o <tytso@mit.edu>
^ permalink raw reply
* [PATCH v2 1/3] ext4: avoid potential buffer over-read in parse_apply_sb_mount_options()
From: Theodore Ts'o via B4 Relay @ 2025-09-17 3:22 UTC (permalink / raw)
To: tytso; +Cc: linux-ext4, linux-api, stable
In-Reply-To: <20250916-tune2fs-v2-0-d594dc7486f0@mit.edu>
From: Theodore Ts'o <tytso@mit.edu>
Unlike other strings in the ext4 superblock, we rely on tune2fs to
make sure s_mount_opts is NUL terminated. Harden
parse_apply_sb_mount_options() by treating s_mount_opts as a potential
__nonstring.
Cc: stable@vger.kernel.org
Fixes: 8b67f04ab9de ("ext4: Add mount options in superblock")
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
fs/ext4/super.c | 17 +++++------------
1 file changed, 5 insertions(+), 12 deletions(-)
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 699c15db28a82f26809bf68533454a242596f0fd..94c98446c84f9a4614971d246ca7f001de610a8a 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2460,7 +2460,7 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
struct ext4_fs_context *m_ctx)
{
struct ext4_sb_info *sbi = EXT4_SB(sb);
- char *s_mount_opts = NULL;
+ char s_mount_opts[65];
struct ext4_fs_context *s_ctx = NULL;
struct fs_context *fc = NULL;
int ret = -ENOMEM;
@@ -2468,15 +2468,11 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
if (!sbi->s_es->s_mount_opts[0])
return 0;
- s_mount_opts = kstrndup(sbi->s_es->s_mount_opts,
- sizeof(sbi->s_es->s_mount_opts),
- GFP_KERNEL);
- if (!s_mount_opts)
- return ret;
+ strscpy_pad(s_mount_opts, sbi->s_es->s_mount_opts);
fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL);
if (!fc)
- goto out_free;
+ return -ENOMEM;
s_ctx = kzalloc(sizeof(struct ext4_fs_context), GFP_KERNEL);
if (!s_ctx)
@@ -2508,11 +2504,8 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
ret = 0;
out_free:
- if (fc) {
- ext4_fc_free(fc);
- kfree(fc);
- }
- kfree(s_mount_opts);
+ ext4_fc_free(fc);
+ kfree(fc);
return ret;
}
--
2.51.0
^ permalink raw reply related
* [PATCH v2 2/3] ext4: add support for 32-bit default reserved uid and gid values
From: Theodore Ts'o via B4 Relay @ 2025-09-17 3:22 UTC (permalink / raw)
To: tytso; +Cc: linux-ext4, linux-api
In-Reply-To: <20250916-tune2fs-v2-0-d594dc7486f0@mit.edu>
From: Theodore Ts'o <tytso@mit.edu>
Support for specifying the default user id and group id that is
allowed to use the reserved block space was added way back when Linux
only supported 16-bit uid's and gid's. (Yeah, that long ago.) It's
not a commonly used feature, but let's add support for 32-bit user and
group id's.
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
fs/ext4/ext4.h | 16 +++++++++++++++-
fs/ext4/super.c | 8 ++++----
2 files changed, 19 insertions(+), 5 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 01a6e2de7fc3ef0e20b039d3200b9c9bd656f59f..4bfcd5f0c74fda30db4009ee28fbee00a2f6b76f 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1442,7 +1442,9 @@ struct ext4_super_block {
__le16 s_encoding; /* Filename charset encoding */
__le16 s_encoding_flags; /* Filename charset encoding flags */
__le32 s_orphan_file_inum; /* Inode for tracking orphan inodes */
- __le32 s_reserved[94]; /* Padding to the end of the block */
+ __le16 s_def_resuid_hi;
+ __le16 s_def_resgid_hi;
+ __le32 s_reserved[93]; /* Padding to the end of the block */
__le32 s_checksum; /* crc32c(superblock) */
};
@@ -1812,6 +1814,18 @@ static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino)
ino <= le32_to_cpu(EXT4_SB(sb)->s_es->s_inodes_count));
}
+static inline int ext4_get_resuid(struct ext4_super_block *es)
+{
+ return(le16_to_cpu(es->s_def_resuid) |
+ (le16_to_cpu(es->s_def_resuid_hi) << 16));
+}
+
+static inline int ext4_get_resgid(struct ext4_super_block *es)
+{
+ return(le16_to_cpu(es->s_def_resgid) |
+ (le16_to_cpu(es->s_def_resgid_hi) << 16));
+}
+
/*
* Returns: sbi->field[index]
* Used to access an array element from the following sbi fields which require
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 94c98446c84f9a4614971d246ca7f001de610a8a..0256c8f7c6cee2b8d9295f2fa9a7acd904382e83 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2951,11 +2951,11 @@ static int _ext4_show_options(struct seq_file *seq, struct super_block *sb,
}
if (nodefs || !uid_eq(sbi->s_resuid, make_kuid(&init_user_ns, EXT4_DEF_RESUID)) ||
- le16_to_cpu(es->s_def_resuid) != EXT4_DEF_RESUID)
+ ext4_get_resuid(es) != EXT4_DEF_RESUID)
SEQ_OPTS_PRINT("resuid=%u",
from_kuid_munged(&init_user_ns, sbi->s_resuid));
if (nodefs || !gid_eq(sbi->s_resgid, make_kgid(&init_user_ns, EXT4_DEF_RESGID)) ||
- le16_to_cpu(es->s_def_resgid) != EXT4_DEF_RESGID)
+ ext4_get_resgid(es) != EXT4_DEF_RESGID)
SEQ_OPTS_PRINT("resgid=%u",
from_kgid_munged(&init_user_ns, sbi->s_resgid));
def_errors = nodefs ? -1 : le16_to_cpu(es->s_errors);
@@ -5270,8 +5270,8 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
ext4_set_def_opts(sb, es);
- sbi->s_resuid = make_kuid(&init_user_ns, le16_to_cpu(es->s_def_resuid));
- sbi->s_resgid = make_kgid(&init_user_ns, le16_to_cpu(es->s_def_resgid));
+ sbi->s_resuid = make_kuid(&init_user_ns, ext4_get_resuid(es));
+ sbi->s_resgid = make_kgid(&init_user_ns, ext4_get_resuid(es));
sbi->s_commit_interval = JBD2_DEFAULT_MAX_COMMIT_AGE * HZ;
sbi->s_min_batch_time = EXT4_DEF_MIN_BATCH_TIME;
sbi->s_max_batch_time = EXT4_DEF_MAX_BATCH_TIME;
--
2.51.0
^ permalink raw reply related
* [PATCH v2 3/3] ext4: implemet new ioctls to set and get superblock parameters
From: Theodore Ts'o via B4 Relay @ 2025-09-17 3:22 UTC (permalink / raw)
To: tytso; +Cc: linux-ext4, linux-api
In-Reply-To: <20250916-tune2fs-v2-0-d594dc7486f0@mit.edu>
From: Theodore Ts'o <tytso@mit.edu>
Implement the EXT4_IOC_GET_TUNE_SB_PARAM and
EXT4_IOC_SET_TUNE_SB_PARAM ioctls, which allow certains superblock
parameters to be set while the file system is mounted, without needing
write access to the block device.
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
fs/ext4/ioctl.c | 312 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
include/uapi/linux/ext4.h | 53 +++++++++++++
2 files changed, 358 insertions(+), 7 deletions(-)
diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index 84e3c73952d72e436429489f5fc8b7ae1c01c7a1..a93a7baae990cc5580d2ddb3ffcc72fe15246978 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -27,14 +27,16 @@
#include "fsmap.h"
#include <trace/events/ext4.h>
-typedef void ext4_update_sb_callback(struct ext4_super_block *es,
- const void *arg);
+typedef void ext4_update_sb_callback(struct ext4_sb_info *sbi,
+ struct ext4_super_block *es,
+ const void *arg);
/*
* Superblock modification callback function for changing file system
* label
*/
-static void ext4_sb_setlabel(struct ext4_super_block *es, const void *arg)
+static void ext4_sb_setlabel(struct ext4_sb_info *sbi,
+ struct ext4_super_block *es, const void *arg)
{
/* Sanity check, this should never happen */
BUILD_BUG_ON(sizeof(es->s_volume_name) < EXT4_LABEL_MAX);
@@ -46,7 +48,8 @@ static void ext4_sb_setlabel(struct ext4_super_block *es, const void *arg)
* Superblock modification callback function for changing file system
* UUID.
*/
-static void ext4_sb_setuuid(struct ext4_super_block *es, const void *arg)
+static void ext4_sb_setuuid(struct ext4_sb_info *sbi,
+ struct ext4_super_block *es, const void *arg)
{
memcpy(es->s_uuid, (__u8 *)arg, UUID_SIZE);
}
@@ -71,7 +74,7 @@ int ext4_update_primary_sb(struct super_block *sb, handle_t *handle,
goto out_err;
lock_buffer(bh);
- func(es, arg);
+ func(sbi, es, arg);
ext4_superblock_csum_set(sb);
unlock_buffer(bh);
@@ -149,7 +152,7 @@ static int ext4_update_backup_sb(struct super_block *sb,
unlock_buffer(bh);
goto out_bh;
}
- func(es, arg);
+ func(EXT4_SB(sb), es, arg);
if (ext4_has_feature_metadata_csum(sb))
es->s_checksum = ext4_superblock_csum(es);
set_buffer_uptodate(bh);
@@ -1230,6 +1233,295 @@ static int ext4_ioctl_setuuid(struct file *filp,
return ret;
}
+
+#define TUNE_OPS_SUPPORTED (EXT4_TUNE_FL_ERRORS_BEHAVIOR | \
+ EXT4_TUNE_FL_MNT_COUNT | EXT4_TUNE_FL_MAX_MNT_COUNT | \
+ EXT4_TUNE_FL_CHECKINTRVAL | EXT4_TUNE_FL_LAST_CHECK_TIME | \
+ EXT4_TUNE_FL_RESERVED_BLOCKS | EXT4_TUNE_FL_RESERVED_UID | \
+ EXT4_TUNE_FL_RESERVED_GID | EXT4_TUNE_FL_DEFAULT_MNT_OPTS | \
+ EXT4_TUNE_FL_DEF_HASH_ALG | EXT4_TUNE_FL_RAID_STRIDE | \
+ EXT4_TUNE_FL_RAID_STRIPE_WIDTH | EXT4_TUNE_FL_MOUNT_OPTS | \
+ EXT4_TUNE_FL_FEATURES | EXT4_TUNE_FL_EDIT_FEATURES | \
+ EXT4_TUNE_FL_FORCE_FSCK | EXT4_TUNE_FL_ENCODING | \
+ EXT4_TUNE_FL_ENCODING_FLAGS)
+
+#define EXT4_TUNE_SET_COMPAT_SUPP \
+ (EXT4_FEATURE_COMPAT_DIR_INDEX | \
+ EXT4_FEATURE_COMPAT_STABLE_INODES)
+#define EXT4_TUNE_SET_INCOMPAT_SUPP \
+ (EXT4_FEATURE_INCOMPAT_EXTENTS | \
+ EXT4_FEATURE_INCOMPAT_EA_INODE | \
+ EXT4_FEATURE_INCOMPAT_ENCRYPT | \
+ EXT4_FEATURE_INCOMPAT_CSUM_SEED | \
+ EXT4_FEATURE_INCOMPAT_LARGEDIR | \
+ EXT4_FEATURE_INCOMPAT_CASEFOLD)
+#define EXT4_TUNE_SET_RO_COMPAT_SUPP \
+ (EXT4_FEATURE_RO_COMPAT_LARGE_FILE | \
+ EXT4_FEATURE_RO_COMPAT_DIR_NLINK | \
+ EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE | \
+ EXT4_FEATURE_RO_COMPAT_PROJECT | \
+ EXT4_FEATURE_RO_COMPAT_VERITY)
+
+#define EXT4_TUNE_CLEAR_COMPAT_SUPP (0)
+#define EXT4_TUNE_CLEAR_INCOMPAT_SUPP (0)
+#define EXT4_TUNE_CLEAR_RO_COMPAT_SUPP (0)
+
+#define SB_ENC_SUPP_MASK (SB_ENC_STRICT_MODE_FL | \
+ SB_ENC_NO_COMPAT_FALLBACK_FL)
+
+static int ext4_ioctl_get_tune_sb(struct ext4_sb_info *sbi,
+ struct ext4_tune_sb_params __user *params)
+{
+ struct ext4_tune_sb_params ret;
+ struct ext4_super_block *es = sbi->s_es;
+
+ memset(&ret, 0, sizeof(ret));
+ ret.set_flags = TUNE_OPS_SUPPORTED;
+ ret.errors_behavior = le16_to_cpu(es->s_errors);
+ ret.mnt_count = le16_to_cpu(es->s_mnt_count);
+ ret.max_mnt_count = le16_to_cpu(es->s_max_mnt_count);
+ ret.checkinterval = le32_to_cpu(es->s_checkinterval);
+ ret.last_check_time = le32_to_cpu(es->s_lastcheck);
+ ret.reserved_blocks = ext4_r_blocks_count(es);
+ ret.blocks_count = ext4_blocks_count(es);
+ ret.reserved_uid = ext4_get_resuid(es);
+ ret.reserved_gid = ext4_get_resgid(es);
+ ret.default_mnt_opts = le32_to_cpu(es->s_default_mount_opts);
+ ret.def_hash_alg = es->s_def_hash_version;
+ ret.raid_stride = le16_to_cpu(es->s_raid_stride);
+ ret.raid_stripe_width = le32_to_cpu(es->s_raid_stripe_width);
+ ret.encoding = le16_to_cpu(es->s_encoding);
+ ret.encoding_flags = le16_to_cpu(es->s_encoding_flags);
+ strscpy_pad(ret.mount_opts, es->s_mount_opts);
+ ret.feature_compat = le32_to_cpu(es->s_feature_compat);
+ ret.feature_incompat = le32_to_cpu(es->s_feature_incompat);
+ ret.feature_ro_compat = le32_to_cpu(es->s_feature_ro_compat);
+ ret.set_feature_compat_mask = EXT4_TUNE_SET_COMPAT_SUPP;
+ ret.set_feature_incompat_mask = EXT4_TUNE_SET_INCOMPAT_SUPP;
+ ret.set_feature_ro_compat_mask = EXT4_TUNE_SET_RO_COMPAT_SUPP;
+ ret.clear_feature_compat_mask = EXT4_TUNE_CLEAR_COMPAT_SUPP;
+ ret.clear_feature_incompat_mask = EXT4_TUNE_CLEAR_INCOMPAT_SUPP;
+ ret.clear_feature_ro_compat_mask = EXT4_TUNE_CLEAR_RO_COMPAT_SUPP;
+ if (copy_to_user(params, &ret, sizeof(ret)))
+ return -EFAULT;
+ return 0;
+}
+
+static void ext4_sb_setparams(struct ext4_sb_info *sbi,
+ struct ext4_super_block *es, const void *arg)
+{
+ const struct ext4_tune_sb_params *params = arg;
+
+ if (params->set_flags & EXT4_TUNE_FL_ERRORS_BEHAVIOR)
+ es->s_errors = cpu_to_le16(params->errors_behavior);
+ if (params->set_flags & EXT4_TUNE_FL_MNT_COUNT)
+ es->s_mnt_count = cpu_to_le16(params->mnt_count);
+ if (params->set_flags & EXT4_TUNE_FL_MAX_MNT_COUNT)
+ es->s_max_mnt_count = cpu_to_le16(params->max_mnt_count);
+ if (params->set_flags & EXT4_TUNE_FL_CHECKINTRVAL)
+ es->s_checkinterval = cpu_to_le32(params->checkinterval);
+ if (params->set_flags & EXT4_TUNE_FL_LAST_CHECK_TIME)
+ es->s_lastcheck = cpu_to_le32(params->last_check_time);
+ if (params->set_flags & EXT4_TUNE_FL_RESERVED_BLOCKS) {
+ ext4_fsblk_t blk = params->reserved_blocks;
+
+ es->s_r_blocks_count_lo = cpu_to_le32((u32)blk);
+ es->s_r_blocks_count_hi = cpu_to_le32(blk >> 32);
+ }
+ if (params->set_flags & EXT4_TUNE_FL_RESERVED_UID) {
+ int uid = params->reserved_uid;
+
+ es->s_def_resuid = cpu_to_le16(uid & 0xFFFF);
+ es->s_def_resuid_hi = cpu_to_le16(uid >> 16);
+ }
+ if (params->set_flags & EXT4_TUNE_FL_RESERVED_GID) {
+ int gid = params->reserved_gid;
+
+ es->s_def_resgid = cpu_to_le16(gid & 0xFFFF);
+ es->s_def_resgid_hi = cpu_to_le16(gid >> 16);
+ }
+ if (params->set_flags & EXT4_TUNE_FL_DEFAULT_MNT_OPTS)
+ es->s_default_mount_opts = cpu_to_le32(params->default_mnt_opts);
+ if (params->set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
+ es->s_def_hash_version = params->def_hash_alg;
+ if (params->set_flags & EXT4_TUNE_FL_RAID_STRIDE)
+ es->s_raid_stride = cpu_to_le16(params->raid_stride);
+ if (params->set_flags & EXT4_TUNE_FL_RAID_STRIPE_WIDTH)
+ es->s_raid_stripe_width =
+ cpu_to_le32(params->raid_stripe_width);
+ if (params->set_flags & EXT4_TUNE_FL_ENCODING)
+ es->s_encoding = cpu_to_le16(params->encoding);
+ if (params->set_flags & EXT4_TUNE_FL_ENCODING_FLAGS)
+ es->s_encoding_flags = cpu_to_le16(params->encoding_flags);
+ strscpy_pad(es->s_mount_opts, params->mount_opts);
+ if (params->set_flags & EXT4_TUNE_FL_EDIT_FEATURES) {
+ es->s_feature_compat |=
+ cpu_to_le32(params->set_feature_compat_mask);
+ es->s_feature_incompat |=
+ cpu_to_le32(params->set_feature_incompat_mask);
+ es->s_feature_ro_compat |=
+ cpu_to_le32(params->set_feature_ro_compat_mask);
+ es->s_feature_compat &=
+ ~cpu_to_le32(params->clear_feature_compat_mask);
+ es->s_feature_incompat &=
+ ~cpu_to_le32(params->clear_feature_incompat_mask);
+ es->s_feature_ro_compat &=
+ ~cpu_to_le32(params->clear_feature_ro_compat_mask);
+ if (params->set_feature_compat_mask &
+ EXT4_FEATURE_COMPAT_DIR_INDEX)
+ es->s_def_hash_version = sbi->s_def_hash_version;
+ if (params->set_feature_incompat_mask &
+ EXT4_FEATURE_INCOMPAT_CSUM_SEED)
+ es->s_checksum_seed = cpu_to_le32(sbi->s_csum_seed);
+ }
+ if (params->set_flags & EXT4_TUNE_FL_FORCE_FSCK)
+ es->s_state |= cpu_to_le16(EXT4_ERROR_FS);
+}
+
+static int ext4_ioctl_set_tune_sb(struct file *filp,
+ struct ext4_tune_sb_params __user *in)
+{
+ struct ext4_tune_sb_params params;
+ struct super_block *sb = file_inode(filp)->i_sb;
+ struct ext4_sb_info *sbi = EXT4_SB(sb);
+ struct ext4_super_block *es = sbi->s_es;
+ int enabling_casefold = 0;
+ int ret;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
+ if (copy_from_user(¶ms, in, sizeof(params)))
+ return -EFAULT;
+
+ if ((params.set_flags & ~TUNE_OPS_SUPPORTED) != 0)
+ return -EOPNOTSUPP;
+
+ if ((params.set_flags & EXT4_TUNE_FL_ERRORS_BEHAVIOR) &&
+ (params.errors_behavior > EXT4_ERRORS_PANIC))
+ return -EINVAL;
+
+ if ((params.set_flags & EXT4_TUNE_FL_RESERVED_BLOCKS) &&
+ (params.reserved_blocks > ext4_blocks_count(sbi->s_es) / 2))
+ return -EINVAL;
+ if ((params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG) &&
+ ((params.def_hash_alg > DX_HASH_LAST) ||
+ (params.def_hash_alg == DX_HASH_SIPHASH)))
+ return -EINVAL;
+ if ((params.set_flags & EXT4_TUNE_FL_FEATURES) &&
+ (params.set_flags & EXT4_TUNE_FL_EDIT_FEATURES))
+ return -EINVAL;
+
+ if (params.set_flags & EXT4_TUNE_FL_FEATURES) {
+ params.set_feature_compat_mask =
+ params.feature_compat &
+ ~le32_to_cpu(es->s_feature_compat);
+ params.set_feature_incompat_mask =
+ params.feature_incompat &
+ ~le32_to_cpu(es->s_feature_incompat);
+ params.set_feature_ro_compat_mask =
+ params.feature_ro_compat &
+ ~le32_to_cpu(es->s_feature_ro_compat);
+ params.clear_feature_compat_mask =
+ ~params.feature_compat &
+ le32_to_cpu(es->s_feature_compat);
+ params.clear_feature_incompat_mask =
+ ~params.feature_incompat &
+ le32_to_cpu(es->s_feature_incompat);
+ params.clear_feature_ro_compat_mask =
+ ~params.feature_ro_compat &
+ le32_to_cpu(es->s_feature_ro_compat);
+ params.set_flags |= EXT4_TUNE_FL_EDIT_FEATURES;
+ }
+ if (params.set_flags & EXT4_TUNE_FL_EDIT_FEATURES) {
+ if ((params.set_feature_compat_mask &
+ ~EXT4_TUNE_SET_COMPAT_SUPP) ||
+ (params.set_feature_incompat_mask &
+ ~EXT4_TUNE_SET_INCOMPAT_SUPP) ||
+ (params.set_feature_ro_compat_mask &
+ ~EXT4_TUNE_SET_RO_COMPAT_SUPP) ||
+ (params.clear_feature_compat_mask &
+ ~EXT4_TUNE_CLEAR_COMPAT_SUPP) ||
+ (params.clear_feature_incompat_mask &
+ ~EXT4_TUNE_CLEAR_INCOMPAT_SUPP) ||
+ (params.clear_feature_ro_compat_mask &
+ ~EXT4_TUNE_CLEAR_RO_COMPAT_SUPP))
+ return -EOPNOTSUPP;
+
+ /*
+ * Filter out the features that are already set from
+ * the set_mask.
+ */
+ params.set_feature_compat_mask &=
+ ~le32_to_cpu(es->s_feature_compat);
+ params.set_feature_incompat_mask &=
+ ~le32_to_cpu(es->s_feature_incompat);
+ params.set_feature_ro_compat_mask &=
+ ~le32_to_cpu(es->s_feature_ro_compat);
+ if ((params.set_feature_incompat_mask &
+ EXT4_FEATURE_INCOMPAT_CASEFOLD)) {
+ enabling_casefold = 1;
+ if (!(params.set_flags & EXT4_TUNE_FL_ENCODING)) {
+ params.encoding = EXT4_ENC_UTF8_12_1;
+ params.set_flags |= EXT4_TUNE_FL_ENCODING;
+ }
+ if (!(params.set_flags & EXT4_TUNE_FL_ENCODING_FLAGS)) {
+ params.encoding_flags = 0;
+ params.set_flags |= EXT4_TUNE_FL_ENCODING_FLAGS;
+ }
+ }
+ if ((params.set_feature_compat_mask &
+ EXT4_FEATURE_COMPAT_DIR_INDEX)) {
+ uuid_t uu;
+
+ memcpy(&uu, sbi->s_hash_seed, UUID_SIZE);
+ if (uuid_is_null(&uu))
+ generate_random_uuid((char *)
+ &sbi->s_hash_seed);
+ if (params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
+ sbi->s_def_hash_version = params.def_hash_alg;
+ else if (sbi->s_def_hash_version == 0)
+ sbi->s_def_hash_version = DX_HASH_HALF_MD4;
+ if (!(es->s_flags &
+ cpu_to_le32(EXT2_FLAGS_UNSIGNED_HASH)) &&
+ !(es->s_flags &
+ cpu_to_le32(EXT2_FLAGS_SIGNED_HASH))) {
+#ifdef __CHAR_UNSIGNED__
+ sbi->s_hash_unsigned = 3;
+#else
+ sbi->s_hash_unsigned = 0;
+#endif
+ }
+ }
+ }
+ if (params.set_flags & EXT4_TUNE_FL_ENCODING) {
+ if (!enabling_casefold)
+ return -EINVAL;
+ if (params.encoding == 0)
+ params.encoding = EXT4_ENC_UTF8_12_1;
+ else if (params.encoding != EXT4_ENC_UTF8_12_1)
+ return -EINVAL;
+ }
+ if (params.set_flags & EXT4_TUNE_FL_ENCODING_FLAGS) {
+ if (!enabling_casefold)
+ return -EINVAL;
+ if (params.encoding_flags & ~SB_ENC_SUPP_MASK)
+ return -EINVAL;
+ }
+
+ ret = mnt_want_write_file(filp);
+ if (ret)
+ return ret;
+
+ ret = ext4_update_superblocks_fn(sb, ext4_sb_setparams, ¶ms);
+ mnt_drop_write_file(filp);
+
+ if (params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
+ sbi->s_def_hash_version = params.def_hash_alg;
+
+ return ret;
+}
+
static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
struct inode *inode = file_inode(filp);
@@ -1616,6 +1908,11 @@ static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
return ext4_ioctl_getuuid(EXT4_SB(sb), (void __user *)arg);
case EXT4_IOC_SETFSUUID:
return ext4_ioctl_setuuid(filp, (const void __user *)arg);
+ case EXT4_IOC_GET_TUNE_SB_PARAM:
+ return ext4_ioctl_get_tune_sb(EXT4_SB(sb),
+ (void __user *)arg);
+ case EXT4_IOC_SET_TUNE_SB_PARAM:
+ return ext4_ioctl_set_tune_sb(filp, (void __user *)arg);
default:
return -ENOTTY;
}
@@ -1703,7 +2000,8 @@ long ext4_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
}
#endif
-static void set_overhead(struct ext4_super_block *es, const void *arg)
+static void set_overhead(struct ext4_sb_info *sbi,
+ struct ext4_super_block *es, const void *arg)
{
es->s_overhead_clusters = cpu_to_le32(*((unsigned long *) arg));
}
diff --git a/include/uapi/linux/ext4.h b/include/uapi/linux/ext4.h
index 1c4c2dd29112cda9f7dc91d917492cffc33ee524..411dcc1e4a35c8c6a10f3768d17b8cc50cff4c34 100644
--- a/include/uapi/linux/ext4.h
+++ b/include/uapi/linux/ext4.h
@@ -33,6 +33,8 @@
#define EXT4_IOC_CHECKPOINT _IOW('f', 43, __u32)
#define EXT4_IOC_GETFSUUID _IOR('f', 44, struct fsuuid)
#define EXT4_IOC_SETFSUUID _IOW('f', 44, struct fsuuid)
+#define EXT4_IOC_GET_TUNE_SB_PARAM _IOR('f', 45, struct ext4_tune_sb_params)
+#define EXT4_IOC_SET_TUNE_SB_PARAM _IOW('f', 46, struct ext4_tune_sb_params)
#define EXT4_IOC_SHUTDOWN _IOR('X', 125, __u32)
@@ -108,6 +110,57 @@ struct ext4_new_group_input {
__u16 unused;
};
+struct ext4_tune_sb_params {
+ __u32 set_flags;
+ __u32 checkinterval;
+ __u16 errors_behavior;
+ __u16 mnt_count;
+ __u16 max_mnt_count;
+ __u16 raid_stride;
+ __u64 last_check_time;
+ __u64 reserved_blocks;
+ __u64 blocks_count;
+ __u32 default_mnt_opts;
+ __u32 reserved_uid;
+ __u32 reserved_gid;
+ __u32 raid_stripe_width;
+ __u16 encoding;
+ __u16 encoding_flags;
+ __u8 def_hash_alg;
+ __u8 pad_1;
+ __u16 pad_2;
+ __u32 feature_compat;
+ __u32 feature_incompat;
+ __u32 feature_ro_compat;
+ __u32 set_feature_compat_mask;
+ __u32 set_feature_incompat_mask;
+ __u32 set_feature_ro_compat_mask;
+ __u32 clear_feature_compat_mask;
+ __u32 clear_feature_incompat_mask;
+ __u32 clear_feature_ro_compat_mask;
+ __u8 mount_opts[64];
+ __u8 pad[64];
+};
+
+#define EXT4_TUNE_FL_ERRORS_BEHAVIOR 0x00000001
+#define EXT4_TUNE_FL_MNT_COUNT 0x00000002
+#define EXT4_TUNE_FL_MAX_MNT_COUNT 0x00000004
+#define EXT4_TUNE_FL_CHECKINTRVAL 0x00000008
+#define EXT4_TUNE_FL_LAST_CHECK_TIME 0x00000010
+#define EXT4_TUNE_FL_RESERVED_BLOCKS 0x00000020
+#define EXT4_TUNE_FL_RESERVED_UID 0x00000040
+#define EXT4_TUNE_FL_RESERVED_GID 0x00000080
+#define EXT4_TUNE_FL_DEFAULT_MNT_OPTS 0x00000100
+#define EXT4_TUNE_FL_DEF_HASH_ALG 0x00000200
+#define EXT4_TUNE_FL_RAID_STRIDE 0x00000400
+#define EXT4_TUNE_FL_RAID_STRIPE_WIDTH 0x00000800
+#define EXT4_TUNE_FL_MOUNT_OPTS 0x00001000
+#define EXT4_TUNE_FL_FEATURES 0x00002000
+#define EXT4_TUNE_FL_EDIT_FEATURES 0x00004000
+#define EXT4_TUNE_FL_FORCE_FSCK 0x00008000
+#define EXT4_TUNE_FL_ENCODING 0x00010000
+#define EXT4_TUNE_FL_ENCODING_FLAGS 0x00020000
+
/*
* Returned by EXT4_IOC_GET_ES_CACHE as an additional possible flag.
* It indicates that the entry in extent status cache is for a hole.
--
2.51.0
^ permalink raw reply related
* Re: [PATCH RESEND 00/62] initrd: remove classic initrd support
From: Jessica Clarke @ 2025-09-16 17:08 UTC (permalink / raw)
To: Askar Safin
Cc: linux-fsdevel, linux-kernel, Linus Torvalds, Greg Kroah-Hartman,
Christian Brauner, Al Viro, Jan Kara, Christoph Hellwig,
Jens Axboe, Andy Shevchenko, Aleksa Sarai, Thomas Weißschuh,
Julian Stecklina, Gao Xiang, Art Nikpal, Andrew Morton,
Eric Curtin, Alexander Graf, Rob Landley, Lennart Poettering,
linux-arch, linux-alpha, linux-snps-arc, linux-arm-kernel,
linux-csky, linux-hexagon, loongarch, linux-m68k, linux-mips,
linux-openrisc, linux-parisc, linuxppc-dev, linux-riscv,
linux-s390, linux-sh, sparclinux, linux-um, x86, Ingo Molnar,
linux-block, initramfs, linux-api, linux-doc, linux-efi,
linux-ext4, Theodore Y . Ts'o, linux-acpi, Michal Simek,
devicetree, Luis Chamberlain, Kees Cook, Thorsten Blum,
Heiko Carstens, patches
In-Reply-To: <20250913003842.41944-1-safinaskar@gmail.com>
On 13 Sep 2025, at 01:37, Askar Safin <safinaskar@gmail.com> wrote:
> [...]
> For example, I renamed the following global variables:
>
> __initramfs_start
> __initramfs_size
> [...]
>
> to:
>
> __builtin_initramfs_start
> __builtin_initramfs_size
I strongly suggest picking different names given __builtin_foo is the
naming scheme used for GNU C builtins/intrinsics. I leave you and
others to bikeshed that one.
Jessica
^ permalink raw reply
* Re: [PATCH v21 4/8] fork: Add shadow stack support to clone3()
From: Yury Khrustalev @ 2025-09-16 12:29 UTC (permalink / raw)
To: Mark Brown
Cc: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan,
linux-kernel, Catalin Marinas, Will Deacon, jannh, Andrew Morton,
Wilco Dijkstra, linux-kselftest, linux-api, Kees Cook
In-Reply-To: <20250916-clone3-shadow-stack-v21-4-910493527013@kernel.org>
On Tue, Sep 16, 2025 at 12:12:09AM +0100, Mark Brown wrote:
> Unlike with the normal stack there is no API for configuring the shadow
> stack for a new thread, instead the kernel will dynamically allocate a
> new shadow stack with the same size as the normal stack. This appears to
> be due to the shadow stack series having been in development since
> before the more extensible clone3() was added rather than anything more
> deliberate.
>
> Add a parameter to clone3() specifying a shadow stack pointer to use
> for the new thread, this is inconsistent with the way we specify the
> normal stack but during review concerns were expressed about having to
> identify where the shadow stack pointer should be placed especially in
> cases where the shadow stack has been previously active. If no shadow
> stack is specified then the existing implicit allocation behaviour is
> maintained.
>
> ...
>
> Update the existing arm64 and x86 implementations to pay attention to
> the newly added arguments, in order to maintain compatibility we use the
> existing behaviour if no shadow stack is specified. Since we are now
> using more fields from the kernel_clone_args we pass that into the
> shadow stack code rather than individual fields.
>
> Portions of the x86 architecture code were written by Rick Edgecombe.
>
> Acked-by: Yury Khrustalev <yury.khrustalev@arm.com>
> Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Mark Brown <broonie@kernel.org>
I've tested this version together with my Glibc patches [1]. No issues
to report.
Tested-by: Yury Khrustalev <yury.khrustalev@arm.com>
[1]: https://inbox.sourceware.org/libc-alpha/20250916122757.2341920-1-yury.khrustalev@arm.com/
> ---
> arch/arm64/mm/gcs.c | 47 +++++++++++++++++++-
> arch/x86/include/asm/shstk.h | 11 +++--
> arch/x86/kernel/process.c | 2 +-
> arch/x86/kernel/shstk.c | 53 ++++++++++++++++++++---
> include/asm-generic/cacheflush.h | 11 +++++
> include/linux/sched/task.h | 17 ++++++++
> include/uapi/linux/sched.h | 9 ++--
> kernel/fork.c | 93 ++++++++++++++++++++++++++++++++++------
> 8 files changed, 217 insertions(+), 26 deletions(-)
>
> diff --git a/arch/arm64/mm/gcs.c b/arch/arm64/mm/gcs.c
> index 3abcbf9adb5c..fd1d5a6655de 100644
> --- a/arch/arm64/mm/gcs.c
> +++ b/arch/arm64/mm/gcs.c
> @@ -43,8 +43,23 @@ int gcs_alloc_thread_stack(struct task_struct *tsk,
> {
> unsigned long addr, size;
>
> - if (!system_supports_gcs())
> + if (!system_supports_gcs()) {
> + if (args->shstk_token)
> + return -EINVAL;
> +
> return 0;
> + }
> +
> + /*
> + * If the user specified a GCS then use it, otherwise fall
> + * back to a default allocation strategy. Validation is done
> + * in arch_shstk_validate_clone().
> + */
> + if (args->shstk_token) {
> + tsk->thread.gcs_base = 0;
> + tsk->thread.gcs_size = 0;
> + return 0;
> + }
>
> if (!task_gcs_el0_enabled(tsk))
> return 0;
> @@ -68,6 +83,36 @@ int gcs_alloc_thread_stack(struct task_struct *tsk,
> return 0;
> }
>
> +static bool gcs_consume_token(struct vm_area_struct *vma, struct page *page,
> + unsigned long user_addr)
> +{
> + u64 expected = GCS_CAP(user_addr);
> + u64 *token = page_address(page) + offset_in_page(user_addr);
> +
> + if (!cmpxchg_to_user_page(vma, page, user_addr, token, expected, 0))
> + return false;
> + set_page_dirty_lock(page);
> +
> + return true;
> +}
> +
> +int arch_shstk_validate_clone(struct task_struct *tsk,
> + struct vm_area_struct *vma,
> + struct page *page,
> + struct kernel_clone_args *args)
> +{
> + unsigned long gcspr_el0;
> + int ret = 0;
> +
> + gcspr_el0 = args->shstk_token;
> + if (!gcs_consume_token(vma, page, gcspr_el0))
> + return -EINVAL;
> +
> + tsk->thread.gcspr_el0 = gcspr_el0 + sizeof(u64);
> +
> + return ret;
> +}
> +
> SYSCALL_DEFINE3(map_shadow_stack, unsigned long, addr, unsigned long, size, unsigned int, flags)
> {
> unsigned long alloc_size;
> diff --git a/arch/x86/include/asm/shstk.h b/arch/x86/include/asm/shstk.h
> index 0f50e0125943..827e983430aa 100644
> --- a/arch/x86/include/asm/shstk.h
> +++ b/arch/x86/include/asm/shstk.h
> @@ -6,6 +6,7 @@
> #include <linux/types.h>
>
> struct task_struct;
> +struct kernel_clone_args;
> struct ksignal;
>
> #ifdef CONFIG_X86_USER_SHADOW_STACK
> @@ -16,8 +17,8 @@ struct thread_shstk {
>
> long shstk_prctl(struct task_struct *task, int option, unsigned long arg2);
> void reset_thread_features(void);
> -unsigned long shstk_alloc_thread_stack(struct task_struct *p, u64 clone_flags,
> - unsigned long stack_size);
> +unsigned long shstk_alloc_thread_stack(struct task_struct *p,
> + const struct kernel_clone_args *args);
> void shstk_free(struct task_struct *p);
> int setup_signal_shadow_stack(struct ksignal *ksig);
> int restore_signal_shadow_stack(void);
> @@ -28,8 +29,10 @@ static inline long shstk_prctl(struct task_struct *task, int option,
> unsigned long arg2) { return -EINVAL; }
> static inline void reset_thread_features(void) {}
> static inline unsigned long shstk_alloc_thread_stack(struct task_struct *p,
> - u64 clone_flags,
> - unsigned long stack_size) { return 0; }
> + const struct kernel_clone_args *args)
> +{
> + return 0;
> +}
> static inline void shstk_free(struct task_struct *p) {}
> static inline int setup_signal_shadow_stack(struct ksignal *ksig) { return 0; }
> static inline int restore_signal_shadow_stack(void) { return 0; }
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index e3a3987b0c4f..e8c8447cc0fd 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -209,7 +209,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
> * is disabled, new_ssp will remain 0, and fpu_clone() will know not to
> * update it.
> */
> - new_ssp = shstk_alloc_thread_stack(p, clone_flags, args->stack_size);
> + new_ssp = shstk_alloc_thread_stack(p, args);
> if (IS_ERR_VALUE(new_ssp))
> return PTR_ERR((void *)new_ssp);
>
> diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c
> index 5eba6c5a6775..56893523b6f2 100644
> --- a/arch/x86/kernel/shstk.c
> +++ b/arch/x86/kernel/shstk.c
> @@ -191,18 +191,61 @@ void reset_thread_features(void)
> current->thread.features_locked = 0;
> }
>
> -unsigned long shstk_alloc_thread_stack(struct task_struct *tsk, u64 clone_flags,
> - unsigned long stack_size)
> +int arch_shstk_validate_clone(struct task_struct *t,
> + struct vm_area_struct *vma,
> + struct page *page,
> + struct kernel_clone_args *args)
> +{
> + void *maddr = page_address(page);
> + unsigned long token;
> + int offset;
> + u64 expected;
> +
> + /*
> + * kernel_clone_args() verification assures token address is 8
> + * byte aligned.
> + */
> + token = args->shstk_token;
> + expected = (token + SS_FRAME_SIZE) | BIT(0);
> + offset = offset_in_page(token);
> +
> + if (!cmpxchg_to_user_page(vma, page, token, (unsigned long *)(maddr + offset),
> + expected, 0))
> + return -EINVAL;
> + set_page_dirty_lock(page);
> +
> + return 0;
> +}
> +
> +unsigned long shstk_alloc_thread_stack(struct task_struct *tsk,
> + const struct kernel_clone_args *args)
> {
> struct thread_shstk *shstk = &tsk->thread.shstk;
> + u64 clone_flags = args->flags;
> unsigned long addr, size;
>
> /*
> * If shadow stack is not enabled on the new thread, skip any
> - * switch to a new shadow stack.
> + * implicit switch to a new shadow stack and reject attempts to
> + * explicitly specify one.
> */
> - if (!features_enabled(ARCH_SHSTK_SHSTK))
> + if (!features_enabled(ARCH_SHSTK_SHSTK)) {
> + if (args->shstk_token)
> + return (unsigned long)ERR_PTR(-EINVAL);
> +
> return 0;
> + }
> +
> + /*
> + * If the user specified a shadow stack then use it, otherwise
> + * fall back to a default allocation strategy. Validation is
> + * done in arch_shstk_validate_clone().
> + */
> + if (args->shstk_token) {
> + shstk->base = 0;
> + shstk->size = 0;
> + return args->shstk_token + 8;
> + }
>
> /*
> * For CLONE_VFORK the child will share the parents shadow stack.
> @@ -222,7 +265,7 @@ unsigned long shstk_alloc_thread_stack(struct task_struct *tsk, u64 clone_flags,
> if (!(clone_flags & CLONE_VM))
> return 0;
>
> - size = adjust_shstk_size(stack_size);
> + size = adjust_shstk_size(args->stack_size);
> addr = alloc_shstk(0, size, 0, false);
> if (IS_ERR_VALUE(addr))
> return addr;
> diff --git a/include/asm-generic/cacheflush.h b/include/asm-generic/cacheflush.h
> index 7ee8a179d103..96cc0c7a5c90 100644
> --- a/include/asm-generic/cacheflush.h
> +++ b/include/asm-generic/cacheflush.h
> @@ -124,4 +124,15 @@ static inline void flush_cache_vunmap(unsigned long start, unsigned long end)
> } while (0)
> #endif
>
> +#ifndef cmpxchg_to_user_page
> +#define cmpxchg_to_user_page(vma, page, vaddr, ptr, old, new) \
> +({ \
> + bool ret; \
> + \
> + ret = try_cmpxchg(ptr, &old, new); \
> + flush_icache_user_page(vma, page, vaddr, sizeof(*ptr)); \
> + ret; \
> +})
> +#endif
> +
> #endif /* _ASM_GENERIC_CACHEFLUSH_H */
> diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
> index 34d6a0e108c3..96fb485ff2dd 100644
> --- a/include/linux/sched/task.h
> +++ b/include/linux/sched/task.h
> @@ -16,6 +16,7 @@ struct task_struct;
> struct rusage;
> union thread_union;
> struct css_set;
> +struct vm_area_struct;
>
> /* All the bits taken by the old clone syscall. */
> #define CLONE_LEGACY_FLAGS 0xffffffffULL
> @@ -44,6 +45,7 @@ struct kernel_clone_args {
> struct cgroup *cgrp;
> struct css_set *cset;
> unsigned int kill_seq;
> + unsigned long shstk_token;
> };
>
> /*
> @@ -226,4 +228,19 @@ static inline void task_unlock(struct task_struct *p)
>
> DEFINE_GUARD(task_lock, struct task_struct *, task_lock(_T), task_unlock(_T))
>
> +#ifdef CONFIG_ARCH_HAS_USER_SHADOW_STACK
> +int arch_shstk_validate_clone(struct task_struct *p,
> + struct vm_area_struct *vma,
> + struct page *page,
> + struct kernel_clone_args *args);
> +#else
> +static inline int arch_shstk_validate_clone(struct task_struct *p,
> + struct vm_area_struct *vma,
> + struct page *page,
> + struct kernel_clone_args *args)
> +{
> + return 0;
> +}
> +#endif
> +
> #endif /* _LINUX_SCHED_TASK_H */
> diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
> index 359a14cc76a4..7e18e7b3df3a 100644
> --- a/include/uapi/linux/sched.h
> +++ b/include/uapi/linux/sched.h
> @@ -84,6 +84,7 @@
> * kernel's limit of nested PID namespaces.
> * @cgroup: If CLONE_INTO_CGROUP is specified set this to
> * a file descriptor for the cgroup.
> + * @shstk_token: Pointer to shadow stack token at top of stack.
> *
> * The structure is versioned by size and thus extensible.
> * New struct members must go at the end of the struct and
> @@ -101,12 +102,14 @@ struct clone_args {
> __aligned_u64 set_tid;
> __aligned_u64 set_tid_size;
> __aligned_u64 cgroup;
> + __aligned_u64 shstk_token;
> };
> #endif
>
> -#define CLONE_ARGS_SIZE_VER0 64 /* sizeof first published struct */
> -#define CLONE_ARGS_SIZE_VER1 80 /* sizeof second published struct */
> -#define CLONE_ARGS_SIZE_VER2 88 /* sizeof third published struct */
> +#define CLONE_ARGS_SIZE_VER0 64 /* sizeof first published struct */
> +#define CLONE_ARGS_SIZE_VER1 80 /* sizeof second published struct */
> +#define CLONE_ARGS_SIZE_VER2 88 /* sizeof third published struct */
> +#define CLONE_ARGS_SIZE_VER3 96 /* sizeof fourth published struct */
>
> /*
> * Scheduling policies
> diff --git a/kernel/fork.c b/kernel/fork.c
> index d6e1fb11eff9..0dbfc8828e08 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1907,6 +1907,51 @@ static bool need_futex_hash_allocate_default(u64 clone_flags)
> return true;
> }
>
> +static int shstk_validate_clone(struct task_struct *p,
> + struct kernel_clone_args *args)
> +{
> + struct mm_struct *mm;
> + struct vm_area_struct *vma;
> + struct page *page;
> + unsigned long addr;
> + int ret;
> +
> + if (!IS_ENABLED(CONFIG_ARCH_HAS_USER_SHADOW_STACK))
> + return 0;
> +
> + if (!args->shstk_token)
> + return 0;
> +
> + mm = get_task_mm(p);
> + if (!mm)
> + return -EFAULT;
> +
> + mmap_read_lock(mm);
> +
> + addr = untagged_addr_remote(mm, args->shstk_token);
> + page = get_user_page_vma_remote(mm, addr, FOLL_FORCE | FOLL_WRITE,
> + &vma);
> + if (IS_ERR(page)) {
> + ret = -EFAULT;
> + goto out;
> + }
> +
> + if (!(vma->vm_flags & VM_SHADOW_STACK) ||
> + !(vma->vm_flags & VM_WRITE)) {
> + ret = -EFAULT;
> + goto out_page;
> + }
> +
> + ret = arch_shstk_validate_clone(p, vma, page, args);
> +
> +out_page:
> + put_page(page);
> +out:
> + mmap_read_unlock(mm);
> + mmput(mm);
> + return ret;
> +}
> +
> /*
> * This creates a new process as a copy of the old one,
> * but does not actually start it yet.
> @@ -2182,6 +2227,9 @@ __latent_entropy struct task_struct *copy_process(
> if (retval)
> goto bad_fork_cleanup_namespaces;
> retval = copy_thread(p, args);
> + if (retval)
> + goto bad_fork_cleanup_io;
> + retval = shstk_validate_clone(p, args);
> if (retval)
> goto bad_fork_cleanup_io;
>
> @@ -2763,7 +2811,9 @@ static noinline int copy_clone_args_from_user(struct kernel_clone_args *kargs,
> CLONE_ARGS_SIZE_VER1);
> BUILD_BUG_ON(offsetofend(struct clone_args, cgroup) !=
> CLONE_ARGS_SIZE_VER2);
> - BUILD_BUG_ON(sizeof(struct clone_args) != CLONE_ARGS_SIZE_VER2);
> + BUILD_BUG_ON(offsetofend(struct clone_args, shstk_token) !=
> + CLONE_ARGS_SIZE_VER3);
> + BUILD_BUG_ON(sizeof(struct clone_args) != CLONE_ARGS_SIZE_VER3);
>
> if (unlikely(usize > PAGE_SIZE))
> return -E2BIG;
> @@ -2796,16 +2846,17 @@ static noinline int copy_clone_args_from_user(struct kernel_clone_args *kargs,
> return -EINVAL;
>
> *kargs = (struct kernel_clone_args){
> - .flags = args.flags,
> - .pidfd = u64_to_user_ptr(args.pidfd),
> - .child_tid = u64_to_user_ptr(args.child_tid),
> - .parent_tid = u64_to_user_ptr(args.parent_tid),
> - .exit_signal = args.exit_signal,
> - .stack = args.stack,
> - .stack_size = args.stack_size,
> - .tls = args.tls,
> - .set_tid_size = args.set_tid_size,
> - .cgroup = args.cgroup,
> + .flags = args.flags,
> + .pidfd = u64_to_user_ptr(args.pidfd),
> + .child_tid = u64_to_user_ptr(args.child_tid),
> + .parent_tid = u64_to_user_ptr(args.parent_tid),
> + .exit_signal = args.exit_signal,
> + .stack = args.stack,
> + .stack_size = args.stack_size,
> + .tls = args.tls,
> + .set_tid_size = args.set_tid_size,
> + .cgroup = args.cgroup,
> + .shstk_token = args.shstk_token,
> };
>
> if (args.set_tid &&
> @@ -2846,6 +2897,24 @@ static inline bool clone3_stack_valid(struct kernel_clone_args *kargs)
> return true;
> }
>
> +/**
> + * clone3_shadow_stack_valid - check and prepare shadow stack
> + * @kargs: kernel clone args
> + *
> + * Verify that shadow stacks are only enabled if supported.
> + */
> +static inline bool clone3_shadow_stack_valid(struct kernel_clone_args *kargs)
> +{
> + if (!kargs->shstk_token)
> + return true;
> +
> + if (!IS_ALIGNED(kargs->shstk_token, sizeof(void *)))
> + return false;
> +
> + /* Fail if the kernel wasn't built with shadow stacks */
> + return IS_ENABLED(CONFIG_ARCH_HAS_USER_SHADOW_STACK);
> +}
> +
> static bool clone3_args_valid(struct kernel_clone_args *kargs)
> {
> /* Verify that no unknown flags are passed along. */
> @@ -2868,7 +2937,7 @@ static bool clone3_args_valid(struct kernel_clone_args *kargs)
> kargs->exit_signal)
> return false;
>
> - if (!clone3_stack_valid(kargs))
> + if (!clone3_stack_valid(kargs) || !clone3_shadow_stack_valid(kargs))
> return false;
>
> return true;
>
> --
> 2.47.2
>
^ permalink raw reply
* Re: [PATCH RESEND 28/62] init: alpha, arc, arm, arm64, csky, m68k, microblaze, mips, nios2, openrisc, parisc, powerpc, s390, sh, sparc, um, x86, xtensa: rename initrd_{start,end} to virt_external_initramfs_{start,end}
From: Rob Herring @ 2025-09-16 3:09 UTC (permalink / raw)
To: Askar Safin
Cc: linux-fsdevel, linux-kernel, Linus Torvalds, Greg Kroah-Hartman,
Christian Brauner, Al Viro, Jan Kara, Christoph Hellwig,
Jens Axboe, Andy Shevchenko, Aleksa Sarai, Thomas Weißschuh,
Julian Stecklina, Gao Xiang, Art Nikpal, Andrew Morton,
Eric Curtin, Alexander Graf, Rob Landley, Lennart Poettering,
linux-arch, linux-alpha, linux-snps-arc, linux-arm-kernel,
linux-csky, linux-hexagon, loongarch, linux-m68k, linux-mips,
linux-openrisc, linux-parisc, linuxppc-dev, linux-riscv,
linux-s390, linux-sh, sparclinux, linux-um, x86, Ingo Molnar,
linux-block, initramfs, linux-api, linux-doc, linux-efi,
linux-ext4, Theodore Y . Ts'o, linux-acpi, Michal Simek,
devicetree, Luis Chamberlain, Kees Cook, Thorsten Blum,
Heiko Carstens, patches
In-Reply-To: <20250913003842.41944-29-safinaskar@gmail.com>
On Sat, Sep 13, 2025 at 12:38:07AM +0000, Askar Safin wrote:
> Rename initrd_start to virt_external_initramfs_start and
> initrd_end to virt_external_initramfs_end.
There's not really any point in listing every arch in the subject.
Rob
^ permalink raw reply
* Re: [PATCH 00/62] initrd: remove classic initrd support
From: Dave Young @ 2025-09-16 1:48 UTC (permalink / raw)
To: Askar Safin
Cc: linux-fsdevel, linux-kernel, Linus Torvalds, Greg Kroah-Hartman,
Christian Brauner, Al Viro, Jan Kara, Christoph Hellwig,
Jens Axboe, Andy Shevchenko, Aleksa Sarai, Thomas Weißschuh,
Julian Stecklina, Gao Xiang, Art Nikpal, Andrew Morton,
Eric Curtin, Alexander Graf, Rob Landley, Lennart Poettering,
linux-arch, linux-alpha, linux-snps-arc, linux-arm-kernel,
linux-csky, linux-hexagon, loongarch, linux-m68k, linux-mips,
linux-openrisc, linux-parisc, linuxppc-dev, linux-riscv,
linux-s390, linux-sh, sparclinux, linux-um, x86, Ingo Molnar,
linux-block, initramfs, linux-api, linux-doc, linux-efi,
linux-ext4, Theodore Y . Ts'o, linux-acpi, Michal Simek,
devicetree, Luis Chamberlain, Kees Cook, Thorsten Blum,
Heiko Carstens, patches
In-Reply-To: <20250912223937.3735076-1-safinaskar@zohomail.com>
Hi,
On Sat, 13 Sept 2025 at 06:42, Askar Safin <safinaskar@zohomail.com> wrote:
>
> Intro
> ====
> This patchset removes classic initrd (initial RAM disk) support,
> which was deprecated in 2020.
> Initramfs still stays, and RAM disk itself (brd) still stays, too.
There is one initrd use case in my mind, it can be extended to co-work
with overlayfs as a kernel built-in solution for initrd(compressed fs
image)+overlayfs. Currently we can use compressed fs images
(squashfs or erofs) within initramfs, and kernel loop mount together
with overlayfs, this works fine but extra pre-mount phase is needed.
Thanks
Dave
^ permalink raw reply
* Re: [PATCH RESEND 00/62] initrd: remove classic initrd support
From: Askar Safin @ 2025-09-16 1:04 UTC (permalink / raw)
To: Christian Brauner
Cc: linux-fsdevel, linux-kernel, Linus Torvalds, Greg Kroah-Hartman,
Al Viro, Jan Kara, Christoph Hellwig, Jens Axboe, Andy Shevchenko,
Aleksa Sarai, Thomas Weißschuh, Julian Stecklina, Gao Xiang,
Art Nikpal, Andrew Morton, Alexander Graf, Rob Landley,
Lennart Poettering, linux-arch, linux-alpha, linux-snps-arc,
linux-arm-kernel, linux-csky, linux-hexagon, loongarch,
linux-m68k, linux-mips, linux-openrisc, linux-parisc,
linuxppc-dev, linux-riscv, linux-s390, linux-sh, sparclinux,
linux-um, x86, Ingo Molnar, linux-block, initramfs, linux-api,
linux-doc, linux-efi, linux-ext4, Theodore Y . Ts'o,
linux-acpi, Michal Simek, devicetree, Luis Chamberlain, Kees Cook,
Thorsten Blum, Heiko Carstens, patches
In-Reply-To: <20250915-modebranche-marken-fc832a25e05d@brauner>
On Mon, Sep 15, 2025 at 4:34 PM Christian Brauner <brauner@kernel.org> wrote:
> Split it up into multiple patch series. Send a first series that
> focusses only on removing the generic infrastructure keeping it as
> contained as possible. Only do non-generic cleanups that are absolutely
> essential for the removal. Then the cleanups can go in separate series
> later.
Ok, I will do this.
I will send a minimal patchset with arch/ changes kept to absolute minimum
or even absent. Nearly all of the changes will be in init/ and docs.
Hopefully it will pass via the VFS tree.
If it gets to kernel release, I will consider sending more patchsets.
--
Askar Safin
^ permalink raw reply
* [PATCH v21 8/8] selftests/clone3: Test shadow stack support
From: Mark Brown @ 2025-09-15 23:12 UTC (permalink / raw)
To: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan
Cc: linux-kernel, Catalin Marinas, Will Deacon, jannh, bsegall,
Andrew Morton, Yury Khrustalev, Wilco Dijkstra, linux-kselftest,
linux-api, Mark Brown, Kees Cook, Shuah Khan
In-Reply-To: <20250916-clone3-shadow-stack-v21-0-910493527013@kernel.org>
Add basic test coverage for specifying the shadow stack for a newly
created thread via clone3(), including coverage of the newly extended
argument structure. We check that a user specified shadow stack can be
provided, and that invalid combinations of parameters are rejected.
In order to facilitate testing on systems without userspace shadow stack
support we manually enable shadow stacks on startup, this is architecture
specific due to the use of an arch_prctl() on x86. Due to interactions with
potential userspace locking of features we actually detect support for
shadow stacks on the running system by attempting to allocate a shadow
stack page during initialisation using map_shadow_stack(), warning if this
succeeds when the enable failed.
In order to allow testing of user configured shadow stacks on
architectures with that feature we need to ensure that we do not return
from the function where the clone3() syscall is called in the child
process, doing so would trigger a shadow stack underflow. To do this we
use inline assembly rather than the standard syscall wrapper to call
clone3(). In order to avoid surprises we also use a syscall rather than
the libc exit() function., this should be overly cautious.
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
tools/testing/selftests/clone3/clone3.c | 143 +++++++++++++++++++++-
tools/testing/selftests/clone3/clone3_selftests.h | 63 ++++++++++
2 files changed, 205 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/clone3/clone3.c b/tools/testing/selftests/clone3/clone3.c
index 5b8b7d640e70..05c3d2dcbf2a 100644
--- a/tools/testing/selftests/clone3/clone3.c
+++ b/tools/testing/selftests/clone3/clone3.c
@@ -3,6 +3,7 @@
/* Based on Christian Brauner's clone3() example */
#define _GNU_SOURCE
+#include <asm/mman.h>
#include <errno.h>
#include <inttypes.h>
#include <linux/types.h>
@@ -11,6 +12,7 @@
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
+#include <sys/mman.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/un.h>
@@ -19,8 +21,12 @@
#include <sched.h>
#include "../kselftest.h"
+#include "../ksft_shstk.h"
#include "clone3_selftests.h"
+static bool shadow_stack_supported;
+static size_t max_supported_args_size;
+
enum test_mode {
CLONE3_ARGS_NO_TEST,
CLONE3_ARGS_ALL_0,
@@ -28,6 +34,10 @@ enum test_mode {
CLONE3_ARGS_INVAL_EXIT_SIGNAL_NEG,
CLONE3_ARGS_INVAL_EXIT_SIGNAL_CSIG,
CLONE3_ARGS_INVAL_EXIT_SIGNAL_NSIG,
+ CLONE3_ARGS_SHADOW_STACK,
+ CLONE3_ARGS_SHADOW_STACK_MISALIGNED,
+ CLONE3_ARGS_SHADOW_STACK_NO_TOKEN,
+ CLONE3_ARGS_SHADOW_STACK_NORMAL_MEMORY,
};
typedef bool (*filter_function)(void);
@@ -44,6 +54,44 @@ struct test {
filter_function filter;
};
+
+/*
+ * We check for shadow stack support by attempting to use
+ * map_shadow_stack() since features may have been locked by the
+ * dynamic linker resulting in spurious errors when we attempt to
+ * enable on startup. We warn if the enable failed.
+ */
+static void test_shadow_stack_supported(void)
+{
+ long ret;
+
+ ret = syscall(__NR_map_shadow_stack, 0, getpagesize(), 0);
+ if (ret == -1) {
+ ksft_print_msg("map_shadow_stack() not supported\n");
+ } else if ((void *)ret == MAP_FAILED) {
+ ksft_print_msg("Failed to map shadow stack\n");
+ } else {
+ ksft_print_msg("Shadow stack supportd\n");
+ shadow_stack_supported = true;
+
+ if (!shadow_stack_enabled)
+ ksft_print_msg("Mapped but did not enable shadow stack\n");
+ }
+}
+
+static void *get_shadow_stack_page(unsigned long flags)
+{
+ unsigned long long page;
+
+ page = syscall(__NR_map_shadow_stack, 0, getpagesize(), flags);
+ if ((void *)page == MAP_FAILED) {
+ ksft_print_msg("map_shadow_stack() failed: %d\n", errno);
+ return 0;
+ }
+
+ return (void *)page;
+}
+
static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
{
struct __clone_args args = {
@@ -57,6 +105,7 @@ static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
} args_ext;
pid_t pid = -1;
+ void *p;
int status;
memset(&args_ext, 0, sizeof(args_ext));
@@ -89,6 +138,26 @@ static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
case CLONE3_ARGS_INVAL_EXIT_SIGNAL_NSIG:
args.exit_signal = 0x00000000000000f0ULL;
break;
+ case CLONE3_ARGS_SHADOW_STACK:
+ p = get_shadow_stack_page(SHADOW_STACK_SET_TOKEN);
+ p += getpagesize() - sizeof(void *);
+ args.shstk_token = (unsigned long long)p;
+ break;
+ case CLONE3_ARGS_SHADOW_STACK_MISALIGNED:
+ p = get_shadow_stack_page(SHADOW_STACK_SET_TOKEN);
+ p += getpagesize() - sizeof(void *) - 1;
+ args.shstk_token = (unsigned long long)p;
+ break;
+ case CLONE3_ARGS_SHADOW_STACK_NORMAL_MEMORY:
+ p = malloc(getpagesize());
+ p += getpagesize() - sizeof(void *);
+ args.shstk_token = (unsigned long long)p;
+ break;
+ case CLONE3_ARGS_SHADOW_STACK_NO_TOKEN:
+ p = get_shadow_stack_page(0);
+ p += getpagesize() - sizeof(void *);
+ args.shstk_token = (unsigned long long)p;
+ break;
}
memcpy(&args_ext.args, &args, sizeof(struct __clone_args));
@@ -102,7 +171,12 @@ static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
if (pid == 0) {
ksft_print_msg("I am the child, my PID is %d\n", getpid());
- _exit(EXIT_SUCCESS);
+ /*
+ * Use a raw syscall to ensure we don't get issues
+ * with manually specified shadow stack and exit handlers.
+ */
+ syscall(__NR_exit, EXIT_SUCCESS);
+ ksft_print_msg("CHILD FAILED TO EXIT PID is %d\n", getpid());
}
ksft_print_msg("I am the parent (%d). My child's pid is %d\n",
@@ -184,6 +258,26 @@ static bool no_timenamespace(void)
return true;
}
+static bool have_shadow_stack(void)
+{
+ if (shadow_stack_supported) {
+ ksft_print_msg("Shadow stack supported\n");
+ return true;
+ }
+
+ return false;
+}
+
+static bool no_shadow_stack(void)
+{
+ if (!shadow_stack_supported) {
+ ksft_print_msg("Shadow stack not supported\n");
+ return true;
+ }
+
+ return false;
+}
+
static size_t page_size_plus_8(void)
{
return getpagesize() + 8;
@@ -327,6 +421,50 @@ static const struct test tests[] = {
.expected = -EINVAL,
.test_mode = CLONE3_ARGS_NO_TEST,
},
+ {
+ .name = "Shadow stack on system with shadow stack",
+ .size = 0,
+ .expected = 0,
+ .e2big_valid = true,
+ .test_mode = CLONE3_ARGS_SHADOW_STACK,
+ .filter = no_shadow_stack,
+ },
+ {
+ .name = "Shadow stack with misaligned address",
+ .flags = CLONE_VM,
+ .size = 0,
+ .expected = -EINVAL,
+ .e2big_valid = true,
+ .test_mode = CLONE3_ARGS_SHADOW_STACK_MISALIGNED,
+ .filter = no_shadow_stack,
+ },
+ {
+ .name = "Shadow stack with normal memory",
+ .flags = CLONE_VM,
+ .size = 0,
+ .expected = -EFAULT,
+ .e2big_valid = true,
+ .test_mode = CLONE3_ARGS_SHADOW_STACK_NORMAL_MEMORY,
+ .filter = no_shadow_stack,
+ },
+ {
+ .name = "Shadow stack with no token",
+ .flags = CLONE_VM,
+ .size = 0,
+ .expected = -EINVAL,
+ .e2big_valid = true,
+ .test_mode = CLONE3_ARGS_SHADOW_STACK_NO_TOKEN,
+ .filter = no_shadow_stack,
+ },
+ {
+ .name = "Shadow stack on system without shadow stack",
+ .flags = CLONE_VM,
+ .size = 0,
+ .expected = -EFAULT,
+ .e2big_valid = true,
+ .test_mode = CLONE3_ARGS_SHADOW_STACK_NORMAL_MEMORY,
+ .filter = have_shadow_stack,
+ },
};
int main(int argc, char *argv[])
@@ -334,9 +472,12 @@ int main(int argc, char *argv[])
size_t size;
int i;
+ enable_shadow_stack();
+
ksft_print_header();
ksft_set_plan(ARRAY_SIZE(tests));
test_clone3_supported();
+ test_shadow_stack_supported();
for (i = 0; i < ARRAY_SIZE(tests); i++)
test_clone3(&tests[i]);
diff --git a/tools/testing/selftests/clone3/clone3_selftests.h b/tools/testing/selftests/clone3/clone3_selftests.h
index 939b26c86d42..147b4ed36b5c 100644
--- a/tools/testing/selftests/clone3/clone3_selftests.h
+++ b/tools/testing/selftests/clone3/clone3_selftests.h
@@ -31,12 +31,75 @@ struct __clone_args {
__aligned_u64 set_tid;
__aligned_u64 set_tid_size;
__aligned_u64 cgroup;
+#ifndef CLONE_ARGS_SIZE_VER2
+#define CLONE_ARGS_SIZE_VER2 88 /* sizeof third published struct */
+#endif
+ __aligned_u64 shstk_token;
+#ifndef CLONE_ARGS_SIZE_VER3
+#define CLONE_ARGS_SIZE_VER3 96 /* sizeof fourth published struct */
+#endif
};
+/*
+ * For architectures with shadow stack support we need to be
+ * absolutely sure that the clone3() syscall will be inline and not a
+ * function call so we open code.
+ */
+#ifdef __x86_64__
+static __always_inline pid_t sys_clone3(struct __clone_args *args, size_t size)
+{
+ register long _num __asm__ ("rax") = __NR_clone3;
+ register long _args __asm__ ("rdi") = (long)(args);
+ register long _size __asm__ ("rsi") = (long)(size);
+ long ret;
+
+ __asm__ volatile (
+ "syscall\n"
+ : "=a"(ret)
+ : "r"(_args), "r"(_size),
+ "0"(_num)
+ : "rcx", "r11", "memory", "cc"
+ );
+
+ if (ret < 0) {
+ errno = -ret;
+ return -1;
+ }
+
+ return ret;
+}
+#elif defined(__aarch64__)
+static __always_inline pid_t sys_clone3(struct __clone_args *args, size_t size)
+{
+ register long _num __asm__ ("x8") = __NR_clone3;
+ register long _args __asm__ ("x0") = (long)(args);
+ register long _size __asm__ ("x1") = (long)(size);
+ register long arg2 __asm__ ("x2") = 0;
+ register long arg3 __asm__ ("x3") = 0;
+ register long arg4 __asm__ ("x4") = 0;
+
+ __asm__ volatile (
+ "svc #0\n"
+ : "=r"(_args)
+ : "r"(_args), "r"(_size),
+ "r"(_num), "r"(arg2),
+ "r"(arg3), "r"(arg4)
+ : "memory", "cc"
+ );
+
+ if ((int)_args < 0) {
+ errno = -((int)_args);
+ return -1;
+ }
+
+ return _args;
+}
+#else
static pid_t sys_clone3(struct __clone_args *args, size_t size)
{
return syscall(__NR_clone3, args, size);
}
+#endif
static inline void test_clone3_supported(void)
{
--
2.47.2
^ permalink raw reply related
* [PATCH v21 7/8] selftests/clone3: Allow tests to flag if -E2BIG is a valid error code
From: Mark Brown @ 2025-09-15 23:12 UTC (permalink / raw)
To: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan
Cc: linux-kernel, Catalin Marinas, Will Deacon, jannh, bsegall,
Andrew Morton, Yury Khrustalev, Wilco Dijkstra, linux-kselftest,
linux-api, Mark Brown, Kees Cook, Kees Cook, Shuah Khan
In-Reply-To: <20250916-clone3-shadow-stack-v21-0-910493527013@kernel.org>
The clone_args structure is extensible, with the syscall passing in the
length of the structure. Inside the kernel we use copy_struct_from_user()
to read the struct but this has the unfortunate side effect of silently
accepting some overrun in the structure size providing the extra data is
all zeros. This means that we can't discover the clone3() features that
the running kernel supports by simply probing with various struct sizes.
We need to check this for the benefit of test systems which run newer
kselftests on old kernels.
Add a flag which can be set on a test to indicate that clone3() may return
-E2BIG due to the use of newer struct versions. Currently no tests need
this but it will become an issue for testing clone3() support for shadow
stacks, the support for shadow stacks is already present on x86.
Reviewed-by: Kees Cook <kees@kernel.org>
Tested-by: Kees Cook <kees@kernel.org>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
tools/testing/selftests/clone3/clone3.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/tools/testing/selftests/clone3/clone3.c b/tools/testing/selftests/clone3/clone3.c
index e066b201fa64..5b8b7d640e70 100644
--- a/tools/testing/selftests/clone3/clone3.c
+++ b/tools/testing/selftests/clone3/clone3.c
@@ -39,6 +39,7 @@ struct test {
size_t size;
size_function size_function;
int expected;
+ bool e2big_valid;
enum test_mode test_mode;
filter_function filter;
};
@@ -146,6 +147,11 @@ static void test_clone3(const struct test *test)
ksft_print_msg("[%d] clone3() with flags says: %d expected %d\n",
getpid(), ret, test->expected);
if (ret != test->expected) {
+ if (test->e2big_valid && ret == -E2BIG) {
+ ksft_print_msg("Test reported -E2BIG\n");
+ ksft_test_result_skip("%s\n", test->name);
+ return;
+ }
ksft_print_msg(
"[%d] Result (%d) is different than expected (%d)\n",
getpid(), ret, test->expected);
--
2.47.2
^ permalink raw reply related
* [PATCH v21 6/8] selftests/clone3: Factor more of main loop into test_clone3()
From: Mark Brown @ 2025-09-15 23:12 UTC (permalink / raw)
To: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan
Cc: linux-kernel, Catalin Marinas, Will Deacon, jannh, bsegall,
Andrew Morton, Yury Khrustalev, Wilco Dijkstra, linux-kselftest,
linux-api, Mark Brown, Kees Cook, Kees Cook, Shuah Khan
In-Reply-To: <20250916-clone3-shadow-stack-v21-0-910493527013@kernel.org>
In order to make it easier to add more configuration for the tests and
more support for runtime detection of when tests can be run pass the
structure describing the tests into test_clone3() rather than picking
the arguments out of it and have that function do all the per-test work.
No functional change.
Reviewed-by: Kees Cook <kees@kernel.org>
Tested-by: Kees Cook <kees@kernel.org>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
tools/testing/selftests/clone3/clone3.c | 77 ++++++++++++++++-----------------
1 file changed, 37 insertions(+), 40 deletions(-)
diff --git a/tools/testing/selftests/clone3/clone3.c b/tools/testing/selftests/clone3/clone3.c
index e61f07973ce5..e066b201fa64 100644
--- a/tools/testing/selftests/clone3/clone3.c
+++ b/tools/testing/selftests/clone3/clone3.c
@@ -30,6 +30,19 @@ enum test_mode {
CLONE3_ARGS_INVAL_EXIT_SIGNAL_NSIG,
};
+typedef bool (*filter_function)(void);
+typedef size_t (*size_function)(void);
+
+struct test {
+ const char *name;
+ uint64_t flags;
+ size_t size;
+ size_function size_function;
+ int expected;
+ enum test_mode test_mode;
+ filter_function filter;
+};
+
static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
{
struct __clone_args args = {
@@ -109,30 +122,40 @@ static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
return 0;
}
-static bool test_clone3(uint64_t flags, size_t size, int expected,
- enum test_mode test_mode)
+static void test_clone3(const struct test *test)
{
+ size_t size;
int ret;
+ if (test->filter && test->filter()) {
+ ksft_test_result_skip("%s\n", test->name);
+ return;
+ }
+
+ if (test->size_function)
+ size = test->size_function();
+ else
+ size = test->size;
+
+ ksft_print_msg("Running test '%s'\n", test->name);
+
ksft_print_msg(
"[%d] Trying clone3() with flags %#" PRIx64 " (size %zu)\n",
- getpid(), flags, size);
- ret = call_clone3(flags, size, test_mode);
+ getpid(), test->flags, size);
+ ret = call_clone3(test->flags, size, test->test_mode);
ksft_print_msg("[%d] clone3() with flags says: %d expected %d\n",
- getpid(), ret, expected);
- if (ret != expected) {
+ getpid(), ret, test->expected);
+ if (ret != test->expected) {
ksft_print_msg(
"[%d] Result (%d) is different than expected (%d)\n",
- getpid(), ret, expected);
- return false;
+ getpid(), ret, test->expected);
+ ksft_test_result_fail("%s\n", test->name);
+ return;
}
- return true;
+ ksft_test_result_pass("%s\n", test->name);
}
-typedef bool (*filter_function)(void);
-typedef size_t (*size_function)(void);
-
static bool not_root(void)
{
if (getuid() != 0) {
@@ -160,16 +183,6 @@ static size_t page_size_plus_8(void)
return getpagesize() + 8;
}
-struct test {
- const char *name;
- uint64_t flags;
- size_t size;
- size_function size_function;
- int expected;
- enum test_mode test_mode;
- filter_function filter;
-};
-
static const struct test tests[] = {
{
.name = "simple clone3()",
@@ -319,24 +332,8 @@ int main(int argc, char *argv[])
ksft_set_plan(ARRAY_SIZE(tests));
test_clone3_supported();
- for (i = 0; i < ARRAY_SIZE(tests); i++) {
- if (tests[i].filter && tests[i].filter()) {
- ksft_test_result_skip("%s\n", tests[i].name);
- continue;
- }
-
- if (tests[i].size_function)
- size = tests[i].size_function();
- else
- size = tests[i].size;
-
- ksft_print_msg("Running test '%s'\n", tests[i].name);
-
- ksft_test_result(test_clone3(tests[i].flags, size,
- tests[i].expected,
- tests[i].test_mode),
- "%s\n", tests[i].name);
- }
+ for (i = 0; i < ARRAY_SIZE(tests); i++)
+ test_clone3(&tests[i]);
ksft_finished();
}
--
2.47.2
^ permalink raw reply related
* [PATCH v21 5/8] selftests/clone3: Remove redundant flushes of output streams
From: Mark Brown @ 2025-09-15 23:12 UTC (permalink / raw)
To: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan
Cc: linux-kernel, Catalin Marinas, Will Deacon, jannh, bsegall,
Andrew Morton, Yury Khrustalev, Wilco Dijkstra, linux-kselftest,
linux-api, Mark Brown, Kees Cook, Kees Cook, Shuah Khan
In-Reply-To: <20250916-clone3-shadow-stack-v21-0-910493527013@kernel.org>
Since there were widespread issues with output not being flushed the
kselftest framework was modified to explicitly set the output streams
unbuffered in commit 58e2847ad2e6 ("selftests: line buffer test
program's stdout") so there is no need to explicitly flush in the clone3
tests.
Reviewed-by: Kees Cook <kees@kernel.org>
Tested-by: Kees Cook <kees@kernel.org>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
tools/testing/selftests/clone3/clone3_selftests.h | 2 --
1 file changed, 2 deletions(-)
diff --git a/tools/testing/selftests/clone3/clone3_selftests.h b/tools/testing/selftests/clone3/clone3_selftests.h
index eeca8005723f..939b26c86d42 100644
--- a/tools/testing/selftests/clone3/clone3_selftests.h
+++ b/tools/testing/selftests/clone3/clone3_selftests.h
@@ -35,8 +35,6 @@ struct __clone_args {
static pid_t sys_clone3(struct __clone_args *args, size_t size)
{
- fflush(stdout);
- fflush(stderr);
return syscall(__NR_clone3, args, size);
}
--
2.47.2
^ permalink raw reply related
* [PATCH v21 4/8] fork: Add shadow stack support to clone3()
From: Mark Brown @ 2025-09-15 23:12 UTC (permalink / raw)
To: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan
Cc: linux-kernel, Catalin Marinas, Will Deacon, jannh, bsegall,
Andrew Morton, Yury Khrustalev, Wilco Dijkstra, linux-kselftest,
linux-api, Mark Brown, Kees Cook
In-Reply-To: <20250916-clone3-shadow-stack-v21-0-910493527013@kernel.org>
Unlike with the normal stack there is no API for configuring the shadow
stack for a new thread, instead the kernel will dynamically allocate a
new shadow stack with the same size as the normal stack. This appears to
be due to the shadow stack series having been in development since
before the more extensible clone3() was added rather than anything more
deliberate.
Add a parameter to clone3() specifying a shadow stack pointer to use
for the new thread, this is inconsistent with the way we specify the
normal stack but during review concerns were expressed about having to
identify where the shadow stack pointer should be placed especially in
cases where the shadow stack has been previously active. If no shadow
stack is specified then the existing implicit allocation behaviour is
maintained.
If a shadow stack pointer is specified then it is required to have an
architecture defined token placed on the stack, this will be consumed by
the new task, the shadow stack is specified by pointing to this token. If
no valid token is present then this will be reported with -EINVAL. This
token prevents new threads being created pointing at the shadow stack of
an existing running thread. On architectures with support for userspace
pivoting of shadow stacks it is expected that the same format and placement
of tokens will be used, this is the case for arm64 and x86.
If the architecture does not support shadow stacks the shadow stack
pointer must be not be specified, architectures that do support the
feature are expected to enforce the same requirement on individual
systems that lack shadow stack support.
Update the existing arm64 and x86 implementations to pay attention to
the newly added arguments, in order to maintain compatibility we use the
existing behaviour if no shadow stack is specified. Since we are now
using more fields from the kernel_clone_args we pass that into the
shadow stack code rather than individual fields.
Portions of the x86 architecture code were written by Rick Edgecombe.
Acked-by: Yury Khrustalev <yury.khrustalev@arm.com>
Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
arch/arm64/mm/gcs.c | 47 +++++++++++++++++++-
arch/x86/include/asm/shstk.h | 11 +++--
arch/x86/kernel/process.c | 2 +-
arch/x86/kernel/shstk.c | 53 ++++++++++++++++++++---
include/asm-generic/cacheflush.h | 11 +++++
include/linux/sched/task.h | 17 ++++++++
include/uapi/linux/sched.h | 9 ++--
kernel/fork.c | 93 ++++++++++++++++++++++++++++++++++------
8 files changed, 217 insertions(+), 26 deletions(-)
diff --git a/arch/arm64/mm/gcs.c b/arch/arm64/mm/gcs.c
index 3abcbf9adb5c..fd1d5a6655de 100644
--- a/arch/arm64/mm/gcs.c
+++ b/arch/arm64/mm/gcs.c
@@ -43,8 +43,23 @@ int gcs_alloc_thread_stack(struct task_struct *tsk,
{
unsigned long addr, size;
- if (!system_supports_gcs())
+ if (!system_supports_gcs()) {
+ if (args->shstk_token)
+ return -EINVAL;
+
return 0;
+ }
+
+ /*
+ * If the user specified a GCS then use it, otherwise fall
+ * back to a default allocation strategy. Validation is done
+ * in arch_shstk_validate_clone().
+ */
+ if (args->shstk_token) {
+ tsk->thread.gcs_base = 0;
+ tsk->thread.gcs_size = 0;
+ return 0;
+ }
if (!task_gcs_el0_enabled(tsk))
return 0;
@@ -68,6 +83,36 @@ int gcs_alloc_thread_stack(struct task_struct *tsk,
return 0;
}
+static bool gcs_consume_token(struct vm_area_struct *vma, struct page *page,
+ unsigned long user_addr)
+{
+ u64 expected = GCS_CAP(user_addr);
+ u64 *token = page_address(page) + offset_in_page(user_addr);
+
+ if (!cmpxchg_to_user_page(vma, page, user_addr, token, expected, 0))
+ return false;
+ set_page_dirty_lock(page);
+
+ return true;
+}
+
+int arch_shstk_validate_clone(struct task_struct *tsk,
+ struct vm_area_struct *vma,
+ struct page *page,
+ struct kernel_clone_args *args)
+{
+ unsigned long gcspr_el0;
+ int ret = 0;
+
+ gcspr_el0 = args->shstk_token;
+ if (!gcs_consume_token(vma, page, gcspr_el0))
+ return -EINVAL;
+
+ tsk->thread.gcspr_el0 = gcspr_el0 + sizeof(u64);
+
+ return ret;
+}
+
SYSCALL_DEFINE3(map_shadow_stack, unsigned long, addr, unsigned long, size, unsigned int, flags)
{
unsigned long alloc_size;
diff --git a/arch/x86/include/asm/shstk.h b/arch/x86/include/asm/shstk.h
index 0f50e0125943..827e983430aa 100644
--- a/arch/x86/include/asm/shstk.h
+++ b/arch/x86/include/asm/shstk.h
@@ -6,6 +6,7 @@
#include <linux/types.h>
struct task_struct;
+struct kernel_clone_args;
struct ksignal;
#ifdef CONFIG_X86_USER_SHADOW_STACK
@@ -16,8 +17,8 @@ struct thread_shstk {
long shstk_prctl(struct task_struct *task, int option, unsigned long arg2);
void reset_thread_features(void);
-unsigned long shstk_alloc_thread_stack(struct task_struct *p, u64 clone_flags,
- unsigned long stack_size);
+unsigned long shstk_alloc_thread_stack(struct task_struct *p,
+ const struct kernel_clone_args *args);
void shstk_free(struct task_struct *p);
int setup_signal_shadow_stack(struct ksignal *ksig);
int restore_signal_shadow_stack(void);
@@ -28,8 +29,10 @@ static inline long shstk_prctl(struct task_struct *task, int option,
unsigned long arg2) { return -EINVAL; }
static inline void reset_thread_features(void) {}
static inline unsigned long shstk_alloc_thread_stack(struct task_struct *p,
- u64 clone_flags,
- unsigned long stack_size) { return 0; }
+ const struct kernel_clone_args *args)
+{
+ return 0;
+}
static inline void shstk_free(struct task_struct *p) {}
static inline int setup_signal_shadow_stack(struct ksignal *ksig) { return 0; }
static inline int restore_signal_shadow_stack(void) { return 0; }
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index e3a3987b0c4f..e8c8447cc0fd 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -209,7 +209,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
* is disabled, new_ssp will remain 0, and fpu_clone() will know not to
* update it.
*/
- new_ssp = shstk_alloc_thread_stack(p, clone_flags, args->stack_size);
+ new_ssp = shstk_alloc_thread_stack(p, args);
if (IS_ERR_VALUE(new_ssp))
return PTR_ERR((void *)new_ssp);
diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c
index 5eba6c5a6775..56893523b6f2 100644
--- a/arch/x86/kernel/shstk.c
+++ b/arch/x86/kernel/shstk.c
@@ -191,18 +191,61 @@ void reset_thread_features(void)
current->thread.features_locked = 0;
}
-unsigned long shstk_alloc_thread_stack(struct task_struct *tsk, u64 clone_flags,
- unsigned long stack_size)
+int arch_shstk_validate_clone(struct task_struct *t,
+ struct vm_area_struct *vma,
+ struct page *page,
+ struct kernel_clone_args *args)
+{
+ void *maddr = page_address(page);
+ unsigned long token;
+ int offset;
+ u64 expected;
+
+ /*
+ * kernel_clone_args() verification assures token address is 8
+ * byte aligned.
+ */
+ token = args->shstk_token;
+ expected = (token + SS_FRAME_SIZE) | BIT(0);
+ offset = offset_in_page(token);
+
+ if (!cmpxchg_to_user_page(vma, page, token, (unsigned long *)(maddr + offset),
+ expected, 0))
+ return -EINVAL;
+ set_page_dirty_lock(page);
+
+ return 0;
+}
+
+unsigned long shstk_alloc_thread_stack(struct task_struct *tsk,
+ const struct kernel_clone_args *args)
{
struct thread_shstk *shstk = &tsk->thread.shstk;
+ u64 clone_flags = args->flags;
unsigned long addr, size;
/*
* If shadow stack is not enabled on the new thread, skip any
- * switch to a new shadow stack.
+ * implicit switch to a new shadow stack and reject attempts to
+ * explicitly specify one.
*/
- if (!features_enabled(ARCH_SHSTK_SHSTK))
+ if (!features_enabled(ARCH_SHSTK_SHSTK)) {
+ if (args->shstk_token)
+ return (unsigned long)ERR_PTR(-EINVAL);
+
return 0;
+ }
+
+ /*
+ * If the user specified a shadow stack then use it, otherwise
+ * fall back to a default allocation strategy. Validation is
+ * done in arch_shstk_validate_clone().
+ */
+ if (args->shstk_token) {
+ shstk->base = 0;
+ shstk->size = 0;
+ return args->shstk_token + 8;
+ }
/*
* For CLONE_VFORK the child will share the parents shadow stack.
@@ -222,7 +265,7 @@ unsigned long shstk_alloc_thread_stack(struct task_struct *tsk, u64 clone_flags,
if (!(clone_flags & CLONE_VM))
return 0;
- size = adjust_shstk_size(stack_size);
+ size = adjust_shstk_size(args->stack_size);
addr = alloc_shstk(0, size, 0, false);
if (IS_ERR_VALUE(addr))
return addr;
diff --git a/include/asm-generic/cacheflush.h b/include/asm-generic/cacheflush.h
index 7ee8a179d103..96cc0c7a5c90 100644
--- a/include/asm-generic/cacheflush.h
+++ b/include/asm-generic/cacheflush.h
@@ -124,4 +124,15 @@ static inline void flush_cache_vunmap(unsigned long start, unsigned long end)
} while (0)
#endif
+#ifndef cmpxchg_to_user_page
+#define cmpxchg_to_user_page(vma, page, vaddr, ptr, old, new) \
+({ \
+ bool ret; \
+ \
+ ret = try_cmpxchg(ptr, &old, new); \
+ flush_icache_user_page(vma, page, vaddr, sizeof(*ptr)); \
+ ret; \
+})
+#endif
+
#endif /* _ASM_GENERIC_CACHEFLUSH_H */
diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index 34d6a0e108c3..96fb485ff2dd 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -16,6 +16,7 @@ struct task_struct;
struct rusage;
union thread_union;
struct css_set;
+struct vm_area_struct;
/* All the bits taken by the old clone syscall. */
#define CLONE_LEGACY_FLAGS 0xffffffffULL
@@ -44,6 +45,7 @@ struct kernel_clone_args {
struct cgroup *cgrp;
struct css_set *cset;
unsigned int kill_seq;
+ unsigned long shstk_token;
};
/*
@@ -226,4 +228,19 @@ static inline void task_unlock(struct task_struct *p)
DEFINE_GUARD(task_lock, struct task_struct *, task_lock(_T), task_unlock(_T))
+#ifdef CONFIG_ARCH_HAS_USER_SHADOW_STACK
+int arch_shstk_validate_clone(struct task_struct *p,
+ struct vm_area_struct *vma,
+ struct page *page,
+ struct kernel_clone_args *args);
+#else
+static inline int arch_shstk_validate_clone(struct task_struct *p,
+ struct vm_area_struct *vma,
+ struct page *page,
+ struct kernel_clone_args *args)
+{
+ return 0;
+}
+#endif
+
#endif /* _LINUX_SCHED_TASK_H */
diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
index 359a14cc76a4..7e18e7b3df3a 100644
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -84,6 +84,7 @@
* kernel's limit of nested PID namespaces.
* @cgroup: If CLONE_INTO_CGROUP is specified set this to
* a file descriptor for the cgroup.
+ * @shstk_token: Pointer to shadow stack token at top of stack.
*
* The structure is versioned by size and thus extensible.
* New struct members must go at the end of the struct and
@@ -101,12 +102,14 @@ struct clone_args {
__aligned_u64 set_tid;
__aligned_u64 set_tid_size;
__aligned_u64 cgroup;
+ __aligned_u64 shstk_token;
};
#endif
-#define CLONE_ARGS_SIZE_VER0 64 /* sizeof first published struct */
-#define CLONE_ARGS_SIZE_VER1 80 /* sizeof second published struct */
-#define CLONE_ARGS_SIZE_VER2 88 /* sizeof third published struct */
+#define CLONE_ARGS_SIZE_VER0 64 /* sizeof first published struct */
+#define CLONE_ARGS_SIZE_VER1 80 /* sizeof second published struct */
+#define CLONE_ARGS_SIZE_VER2 88 /* sizeof third published struct */
+#define CLONE_ARGS_SIZE_VER3 96 /* sizeof fourth published struct */
/*
* Scheduling policies
diff --git a/kernel/fork.c b/kernel/fork.c
index d6e1fb11eff9..0dbfc8828e08 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1907,6 +1907,51 @@ static bool need_futex_hash_allocate_default(u64 clone_flags)
return true;
}
+static int shstk_validate_clone(struct task_struct *p,
+ struct kernel_clone_args *args)
+{
+ struct mm_struct *mm;
+ struct vm_area_struct *vma;
+ struct page *page;
+ unsigned long addr;
+ int ret;
+
+ if (!IS_ENABLED(CONFIG_ARCH_HAS_USER_SHADOW_STACK))
+ return 0;
+
+ if (!args->shstk_token)
+ return 0;
+
+ mm = get_task_mm(p);
+ if (!mm)
+ return -EFAULT;
+
+ mmap_read_lock(mm);
+
+ addr = untagged_addr_remote(mm, args->shstk_token);
+ page = get_user_page_vma_remote(mm, addr, FOLL_FORCE | FOLL_WRITE,
+ &vma);
+ if (IS_ERR(page)) {
+ ret = -EFAULT;
+ goto out;
+ }
+
+ if (!(vma->vm_flags & VM_SHADOW_STACK) ||
+ !(vma->vm_flags & VM_WRITE)) {
+ ret = -EFAULT;
+ goto out_page;
+ }
+
+ ret = arch_shstk_validate_clone(p, vma, page, args);
+
+out_page:
+ put_page(page);
+out:
+ mmap_read_unlock(mm);
+ mmput(mm);
+ return ret;
+}
+
/*
* This creates a new process as a copy of the old one,
* but does not actually start it yet.
@@ -2182,6 +2227,9 @@ __latent_entropy struct task_struct *copy_process(
if (retval)
goto bad_fork_cleanup_namespaces;
retval = copy_thread(p, args);
+ if (retval)
+ goto bad_fork_cleanup_io;
+ retval = shstk_validate_clone(p, args);
if (retval)
goto bad_fork_cleanup_io;
@@ -2763,7 +2811,9 @@ static noinline int copy_clone_args_from_user(struct kernel_clone_args *kargs,
CLONE_ARGS_SIZE_VER1);
BUILD_BUG_ON(offsetofend(struct clone_args, cgroup) !=
CLONE_ARGS_SIZE_VER2);
- BUILD_BUG_ON(sizeof(struct clone_args) != CLONE_ARGS_SIZE_VER2);
+ BUILD_BUG_ON(offsetofend(struct clone_args, shstk_token) !=
+ CLONE_ARGS_SIZE_VER3);
+ BUILD_BUG_ON(sizeof(struct clone_args) != CLONE_ARGS_SIZE_VER3);
if (unlikely(usize > PAGE_SIZE))
return -E2BIG;
@@ -2796,16 +2846,17 @@ static noinline int copy_clone_args_from_user(struct kernel_clone_args *kargs,
return -EINVAL;
*kargs = (struct kernel_clone_args){
- .flags = args.flags,
- .pidfd = u64_to_user_ptr(args.pidfd),
- .child_tid = u64_to_user_ptr(args.child_tid),
- .parent_tid = u64_to_user_ptr(args.parent_tid),
- .exit_signal = args.exit_signal,
- .stack = args.stack,
- .stack_size = args.stack_size,
- .tls = args.tls,
- .set_tid_size = args.set_tid_size,
- .cgroup = args.cgroup,
+ .flags = args.flags,
+ .pidfd = u64_to_user_ptr(args.pidfd),
+ .child_tid = u64_to_user_ptr(args.child_tid),
+ .parent_tid = u64_to_user_ptr(args.parent_tid),
+ .exit_signal = args.exit_signal,
+ .stack = args.stack,
+ .stack_size = args.stack_size,
+ .tls = args.tls,
+ .set_tid_size = args.set_tid_size,
+ .cgroup = args.cgroup,
+ .shstk_token = args.shstk_token,
};
if (args.set_tid &&
@@ -2846,6 +2897,24 @@ static inline bool clone3_stack_valid(struct kernel_clone_args *kargs)
return true;
}
+/**
+ * clone3_shadow_stack_valid - check and prepare shadow stack
+ * @kargs: kernel clone args
+ *
+ * Verify that shadow stacks are only enabled if supported.
+ */
+static inline bool clone3_shadow_stack_valid(struct kernel_clone_args *kargs)
+{
+ if (!kargs->shstk_token)
+ return true;
+
+ if (!IS_ALIGNED(kargs->shstk_token, sizeof(void *)))
+ return false;
+
+ /* Fail if the kernel wasn't built with shadow stacks */
+ return IS_ENABLED(CONFIG_ARCH_HAS_USER_SHADOW_STACK);
+}
+
static bool clone3_args_valid(struct kernel_clone_args *kargs)
{
/* Verify that no unknown flags are passed along. */
@@ -2868,7 +2937,7 @@ static bool clone3_args_valid(struct kernel_clone_args *kargs)
kargs->exit_signal)
return false;
- if (!clone3_stack_valid(kargs))
+ if (!clone3_stack_valid(kargs) || !clone3_shadow_stack_valid(kargs))
return false;
return true;
--
2.47.2
^ permalink raw reply related
* [PATCH v21 3/8] selftests: Provide helper header for shadow stack testing
From: Mark Brown @ 2025-09-15 23:12 UTC (permalink / raw)
To: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan
Cc: linux-kernel, Catalin Marinas, Will Deacon, jannh, bsegall,
Andrew Morton, Yury Khrustalev, Wilco Dijkstra, linux-kselftest,
linux-api, Mark Brown, Kees Cook, Kees Cook, Shuah Khan
In-Reply-To: <20250916-clone3-shadow-stack-v21-0-910493527013@kernel.org>
While almost all users of shadow stacks should be relying on the dynamic
linker and libc to enable the feature there are several low level test
programs where it is useful to enable without any libc support, allowing
testing without full system enablement. This low level testing is helpful
during bringup of the support itself, and also in enabling coverage by
automated testing without needing all system components in the target root
filesystems to have enablement.
Provide a header with helpers for this purpose, intended for use only by
test programs directly exercising shadow stack interfaces.
Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Reviewed-by: Kees Cook <kees@kernel.org>
Tested-by: Kees Cook <kees@kernel.org>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
tools/testing/selftests/ksft_shstk.h | 98 ++++++++++++++++++++++++++++++++++++
1 file changed, 98 insertions(+)
diff --git a/tools/testing/selftests/ksft_shstk.h b/tools/testing/selftests/ksft_shstk.h
new file mode 100644
index 000000000000..fecf91218ea5
--- /dev/null
+++ b/tools/testing/selftests/ksft_shstk.h
@@ -0,0 +1,98 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Helpers for shadow stack enablement, this is intended to only be
+ * used by low level test programs directly exercising interfaces for
+ * working with shadow stacks.
+ *
+ * Copyright (C) 2024 ARM Ltd.
+ */
+
+#ifndef __KSFT_SHSTK_H
+#define __KSFT_SHSTK_H
+
+#include <asm/mman.h>
+
+/* This is currently only defined for x86 */
+#ifndef SHADOW_STACK_SET_TOKEN
+#define SHADOW_STACK_SET_TOKEN (1ULL << 0)
+#endif
+
+static bool shadow_stack_enabled;
+
+#ifdef __x86_64__
+#define ARCH_SHSTK_ENABLE 0x5001
+#define ARCH_SHSTK_SHSTK (1ULL << 0)
+
+#define ARCH_PRCTL(arg1, arg2) \
+({ \
+ long _ret; \
+ register long _num asm("eax") = __NR_arch_prctl; \
+ register long _arg1 asm("rdi") = (long)(arg1); \
+ register long _arg2 asm("rsi") = (long)(arg2); \
+ \
+ asm volatile ( \
+ "syscall\n" \
+ : "=a"(_ret) \
+ : "r"(_arg1), "r"(_arg2), \
+ "0"(_num) \
+ : "rcx", "r11", "memory", "cc" \
+ ); \
+ _ret; \
+})
+
+#define ENABLE_SHADOW_STACK
+static __always_inline void enable_shadow_stack(void)
+{
+ int ret = ARCH_PRCTL(ARCH_SHSTK_ENABLE, ARCH_SHSTK_SHSTK);
+ if (ret == 0)
+ shadow_stack_enabled = true;
+}
+
+#endif
+
+#ifdef __aarch64__
+#define PR_SET_SHADOW_STACK_STATUS 75
+# define PR_SHADOW_STACK_ENABLE (1UL << 0)
+
+#define my_syscall2(num, arg1, arg2) \
+({ \
+ register long _num __asm__ ("x8") = (num); \
+ register long _arg1 __asm__ ("x0") = (long)(arg1); \
+ register long _arg2 __asm__ ("x1") = (long)(arg2); \
+ register long _arg3 __asm__ ("x2") = 0; \
+ register long _arg4 __asm__ ("x3") = 0; \
+ register long _arg5 __asm__ ("x4") = 0; \
+ \
+ __asm__ volatile ( \
+ "svc #0\n" \
+ : "=r"(_arg1) \
+ : "r"(_arg1), "r"(_arg2), \
+ "r"(_arg3), "r"(_arg4), \
+ "r"(_arg5), "r"(_num) \
+ : "memory", "cc" \
+ ); \
+ _arg1; \
+})
+
+#define ENABLE_SHADOW_STACK
+static __always_inline void enable_shadow_stack(void)
+{
+ int ret;
+
+ ret = my_syscall2(__NR_prctl, PR_SET_SHADOW_STACK_STATUS,
+ PR_SHADOW_STACK_ENABLE);
+ if (ret == 0)
+ shadow_stack_enabled = true;
+}
+
+#endif
+
+#ifndef __NR_map_shadow_stack
+#define __NR_map_shadow_stack 453
+#endif
+
+#ifndef ENABLE_SHADOW_STACK
+static inline void enable_shadow_stack(void) { }
+#endif
+
+#endif
--
2.47.2
^ permalink raw reply related
* [PATCH v21 2/8] Documentation: userspace-api: Add shadow stack API documentation
From: Mark Brown @ 2025-09-15 23:12 UTC (permalink / raw)
To: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan
Cc: linux-kernel, Catalin Marinas, Will Deacon, jannh, bsegall,
Andrew Morton, Yury Khrustalev, Wilco Dijkstra, linux-kselftest,
linux-api, Mark Brown, Kees Cook, Kees Cook, Shuah Khan
In-Reply-To: <20250916-clone3-shadow-stack-v21-0-910493527013@kernel.org>
There are a number of architectures with shadow stack features which we are
presenting to userspace with as consistent an API as we can (though there
are some architecture specifics). Especially given that there are some
important considerations for userspace code interacting directly with the
feature let's provide some documentation covering the common aspects.
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Kees Cook <kees@kernel.org>
Tested-by: Kees Cook <kees@kernel.org>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Acked-by: Yury Khrustalev <yury.khrustalev@arm.com>
Reviewed-by: Deepak Gupta <debug@rivosinc.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
Documentation/userspace-api/index.rst | 1 +
Documentation/userspace-api/shadow_stack.rst | 44 ++++++++++++++++++++++++++++
2 files changed, 45 insertions(+)
diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst
index b8c73be4fb11..0167e59b541e 100644
--- a/Documentation/userspace-api/index.rst
+++ b/Documentation/userspace-api/index.rst
@@ -62,6 +62,7 @@ Everything else
ELF
netlink/index
+ shadow_stack
sysfs-platform_profile
vduse
futex2
diff --git a/Documentation/userspace-api/shadow_stack.rst b/Documentation/userspace-api/shadow_stack.rst
new file mode 100644
index 000000000000..42617d0470ba
--- /dev/null
+++ b/Documentation/userspace-api/shadow_stack.rst
@@ -0,0 +1,44 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=============
+Shadow Stacks
+=============
+
+Introduction
+============
+
+Several architectures have features which provide backward edge
+control flow protection through a hardware maintained stack, only
+writable by userspace through very limited operations. This feature
+is referred to as shadow stacks on Linux, on x86 it is part of Intel
+Control Enforcement Technology (CET), on arm64 it is Guarded Control
+Stacks feature (FEAT_GCS) and for RISC-V it is the Zicfiss extension.
+It is expected that this feature will normally be managed by the
+system dynamic linker and libc in ways broadly transparent to
+application code, this document covers interfaces and considerations.
+
+
+Enabling
+========
+
+Shadow stacks default to disabled when a userspace process is
+executed, they can be enabled for the current thread with a syscall:
+
+ - For x86 the ARCH_SHSTK_ENABLE arch_prctl()
+ - For other architectures the PR_SET_SHADOW_STACK_ENABLE prctl()
+
+It is expected that this will normally be done by the dynamic linker.
+Any new threads created by a thread with shadow stacks enabled will
+themselves have shadow stacks enabled.
+
+
+Enablement considerations
+=========================
+
+- Returning from the function that enables shadow stacks without first
+ disabling them will cause a shadow stack exception. This includes
+ any syscall wrapper or other library functions, the syscall will need
+ to be inlined.
+- A lock feature allows userspace to prevent disabling of shadow stacks.
+- Those that change the stack context like longjmp() or use of ucontext
+ changes on signal return will need support from libc.
--
2.47.2
^ permalink raw reply related
* [PATCH v21 1/8] arm64/gcs: Return a success value from gcs_alloc_thread_stack()
From: Mark Brown @ 2025-09-15 23:12 UTC (permalink / raw)
To: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan
Cc: linux-kernel, Catalin Marinas, Will Deacon, jannh, bsegall,
Andrew Morton, Yury Khrustalev, Wilco Dijkstra, linux-kselftest,
linux-api, Mark Brown, Kees Cook
In-Reply-To: <20250916-clone3-shadow-stack-v21-0-910493527013@kernel.org>
Currently as a result of templating from x86 code gcs_alloc_thread_stack()
returns a pointer as an unsigned int however on arm64 we don't actually use
this pointer value as anything other than a pass/fail flag. Simplify the
interface to just return an int with 0 on success and a negative error code
on failure.
Acked-by: Deepak Gupta <debug@rivosinc.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
arch/arm64/include/asm/gcs.h | 8 ++++----
arch/arm64/kernel/process.c | 8 ++++----
arch/arm64/mm/gcs.c | 8 ++++----
3 files changed, 12 insertions(+), 12 deletions(-)
diff --git a/arch/arm64/include/asm/gcs.h b/arch/arm64/include/asm/gcs.h
index 5bc432234d3a..b4bbec9382a1 100644
--- a/arch/arm64/include/asm/gcs.h
+++ b/arch/arm64/include/asm/gcs.h
@@ -64,8 +64,8 @@ static inline bool task_gcs_el0_enabled(struct task_struct *task)
void gcs_set_el0_mode(struct task_struct *task);
void gcs_free(struct task_struct *task);
void gcs_preserve_current_state(void);
-unsigned long gcs_alloc_thread_stack(struct task_struct *tsk,
- const struct kernel_clone_args *args);
+int gcs_alloc_thread_stack(struct task_struct *tsk,
+ const struct kernel_clone_args *args);
static inline int gcs_check_locked(struct task_struct *task,
unsigned long new_val)
@@ -91,8 +91,8 @@ static inline bool task_gcs_el0_enabled(struct task_struct *task)
static inline void gcs_set_el0_mode(struct task_struct *task) { }
static inline void gcs_free(struct task_struct *task) { }
static inline void gcs_preserve_current_state(void) { }
-static inline unsigned long gcs_alloc_thread_stack(struct task_struct *tsk,
- const struct kernel_clone_args *args)
+static inline int gcs_alloc_thread_stack(struct task_struct *tsk,
+ const struct kernel_clone_args *args)
{
return -ENOTSUPP;
}
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index fba7ca102a8c..4dadc70df16b 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -299,7 +299,7 @@ static void flush_gcs(void)
static int copy_thread_gcs(struct task_struct *p,
const struct kernel_clone_args *args)
{
- unsigned long gcs;
+ int ret;
if (!system_supports_gcs())
return 0;
@@ -310,9 +310,9 @@ static int copy_thread_gcs(struct task_struct *p,
p->thread.gcs_el0_mode = current->thread.gcs_el0_mode;
p->thread.gcs_el0_locked = current->thread.gcs_el0_locked;
- gcs = gcs_alloc_thread_stack(p, args);
- if (IS_ERR_VALUE(gcs))
- return PTR_ERR((void *)gcs);
+ ret = gcs_alloc_thread_stack(p, args);
+ if (ret != 0)
+ return ret;
return 0;
}
diff --git a/arch/arm64/mm/gcs.c b/arch/arm64/mm/gcs.c
index 6e93f78de79b..3abcbf9adb5c 100644
--- a/arch/arm64/mm/gcs.c
+++ b/arch/arm64/mm/gcs.c
@@ -38,8 +38,8 @@ static unsigned long gcs_size(unsigned long size)
return max(PAGE_SIZE, size);
}
-unsigned long gcs_alloc_thread_stack(struct task_struct *tsk,
- const struct kernel_clone_args *args)
+int gcs_alloc_thread_stack(struct task_struct *tsk,
+ const struct kernel_clone_args *args)
{
unsigned long addr, size;
@@ -59,13 +59,13 @@ unsigned long gcs_alloc_thread_stack(struct task_struct *tsk,
size = gcs_size(size);
addr = alloc_gcs(0, size);
if (IS_ERR_VALUE(addr))
- return addr;
+ return PTR_ERR((void *)addr);
tsk->thread.gcs_base = addr;
tsk->thread.gcs_size = size;
tsk->thread.gcspr_el0 = addr + size - sizeof(u64);
- return addr;
+ return 0;
}
SYSCALL_DEFINE3(map_shadow_stack, unsigned long, addr, unsigned long, size, unsigned int, flags)
--
2.47.2
^ permalink raw reply related
* [PATCH v21 0/8] fork: Support shadow stacks in clone3()
From: Mark Brown @ 2025-09-15 23:12 UTC (permalink / raw)
To: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan
Cc: linux-kernel, Catalin Marinas, Will Deacon, jannh, bsegall,
Andrew Morton, Yury Khrustalev, Wilco Dijkstra, linux-kselftest,
linux-api, Mark Brown, Kees Cook, Kees Cook, Shuah Khan
[ I think at this point everyone is OK with the ABI, and the x86
implementation has been tested so hopefully we are near to being
able to get this merged? If there are any outstanding issues let
me know and I can look at addressing them. The one possible issue
I am aware of is that the RISC-V shadow stack support was briefly
in -next but got dropped along with the general RISC-V issues during
the last merge window, rebasing for that is still in progress. I
guess ideally this could be applied on a branch and then pulled into
the RISC-V tree? ]
The kernel has recently added support for shadow stacks, currently
x86 only using their CET feature but both arm64 and RISC-V have
equivalent features (GCS and Zicfiss respectively), I am actively
working on GCS[1]. With shadow stacks the hardware maintains an
additional stack containing only the return addresses for branch
instructions which is not generally writeable by userspace and ensures
that any returns are to the recorded addresses. This provides some
protection against ROP attacks and making it easier to collect call
stacks. These shadow stacks are allocated in the address space of the
userspace process.
Our API for shadow stacks does not currently offer userspace any
flexiblity for managing the allocation of shadow stacks for newly
created threads, instead the kernel allocates a new shadow stack with
the same size as the normal stack whenever a thread is created with the
feature enabled. The stacks allocated in this way are freed by the
kernel when the thread exits or shadow stacks are disabled for the
thread. This lack of flexibility and control isn't ideal, in the vast
majority of cases the shadow stack will be over allocated and the
implicit allocation and deallocation is not consistent with other
interfaces. As far as I can tell the interface is done in this manner
mainly because the shadow stack patches were in development since before
clone3() was implemented.
Since clone3() is readily extensible let's add support for specifying a
shadow stack when creating a new thread or process, keeping the current
implicit allocation behaviour if one is not specified either with
clone3() or through the use of clone(). The user must provide a shadow
stack pointer, this must point to memory mapped for use as a shadow
stackby map_shadow_stack() with an architecture specified shadow stack
token at the top of the stack.
Yuri Khrustalev has raised questions from the libc side regarding
discoverability of extended clone3() structure sizes[2], this seems like
a general issue with clone3(). There was a suggestion to add a hwcap on
arm64 which isn't ideal but is doable there, though architecture
specific mechanisms would also be needed for x86 (and RISC-V if it's
support gets merged before this does). The idea has, however, had
strong pushback from the architecture maintainers and it is possible to
detect support for this in clone3() by attempting a call with a
misaligned shadow stack pointer specified so no hwcap has been added.
[1] https://lore.kernel.org/linux-arm-kernel/20241001-arm64-gcs-v13-0-222b78d87eee@kernel.org/T/#mc58f97f27461749ccf400ebabf6f9f937116a86b
[2] https://lore.kernel.org/r/aCs65ccRQtJBnZ_5@arm.com
Signed-off-by: Mark Brown <broonie@kernel.org>
---
Changes in v21:
- Rebase onto https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git kernel-6.18.clone3
- Rename shadow_stack_token to shstk_token, since it's a simple rename I've
kept the acks and reviews but I dropped the tested-bys just to be safe.
- Link to v20: https://lore.kernel.org/r/20250902-clone3-shadow-stack-v20-0-4d9fff1c53e7@kernel.org
Changes in v20:
- Comment fixes and clarifications in x86 arch_shstk_validate_clone()
from Rick Edgecombe.
- Spelling fix in documentation.
- Link to v19: https://lore.kernel.org/r/20250819-clone3-shadow-stack-v19-0-bc957075479b@kernel.org
Changes in v19:
- Rebase onto v6.17-rc1.
- Link to v18: https://lore.kernel.org/r/20250702-clone3-shadow-stack-v18-0-7965d2b694db@kernel.org
Changes in v18:
- Rebase onto v6.16-rc3.
- Thanks to pointers from Yuri Khrustalev this version has been tested
on x86 so I have removed the RFT tag.
- Clarify clone3_shadow_stack_valid() comment about the Kconfig check.
- Remove redundant GCSB DSYNCs in arm64 code.
- Fix token validation on x86.
- Link to v17: https://lore.kernel.org/r/20250609-clone3-shadow-stack-v17-0-8840ed97ff6f@kernel.org
Changes in v17:
- Rebase onto v6.16-rc1.
- Link to v16: https://lore.kernel.org/r/20250416-clone3-shadow-stack-v16-0-2ffc9ca3917b@kernel.org
Changes in v16:
- Rebase onto v6.15-rc2.
- Roll in fixes from x86 testing from Rick Edgecombe.
- Rework so that the argument is shadow_stack_token.
- Link to v15: https://lore.kernel.org/r/20250408-clone3-shadow-stack-v15-0-3fa245c6e3be@kernel.org
Changes in v15:
- Rebase onto v6.15-rc1.
- Link to v14: https://lore.kernel.org/r/20250206-clone3-shadow-stack-v14-0-805b53af73b9@kernel.org
Changes in v14:
- Rebase onto v6.14-rc1.
- Link to v13: https://lore.kernel.org/r/20241203-clone3-shadow-stack-v13-0-93b89a81a5ed@kernel.org
Changes in v13:
- Rebase onto v6.13-rc1.
- Link to v12: https://lore.kernel.org/r/20241031-clone3-shadow-stack-v12-0-7183eb8bee17@kernel.org
Changes in v12:
- Add the regular prctl() to the userspace API document since arm64
support is queued in -next.
- Link to v11: https://lore.kernel.org/r/20241005-clone3-shadow-stack-v11-0-2a6a2bd6d651@kernel.org
Changes in v11:
- Rebase onto arm64 for-next/gcs, which is based on v6.12-rc1, and
integrate arm64 support.
- Rework the interface to specify a shadow stack pointer rather than a
base and size like we do for the regular stack.
- Link to v10: https://lore.kernel.org/r/20240821-clone3-shadow-stack-v10-0-06e8797b9445@kernel.org
Changes in v10:
- Integrate fixes & improvements for the x86 implementation from Rick
Edgecombe.
- Require that the shadow stack be VM_WRITE.
- Require that the shadow stack base and size be sizeof(void *) aligned.
- Clean up trailing newline.
- Link to v9: https://lore.kernel.org/r/20240819-clone3-shadow-stack-v9-0-962d74f99464@kernel.org
Changes in v9:
- Pull token validation earlier and report problems with an error return
to parent rather than signal delivery to the child.
- Verify that the top of the supplied shadow stack is VM_SHADOW_STACK.
- Rework token validation to only do the page mapping once.
- Drop no longer needed support for testing for signals in selftest.
- Fix typo in comments.
- Link to v8: https://lore.kernel.org/r/20240808-clone3-shadow-stack-v8-0-0acf37caf14c@kernel.org
Changes in v8:
- Fix token verification with user specified shadow stack.
- Don't track user managed shadow stacks for child processes.
- Link to v7: https://lore.kernel.org/r/20240731-clone3-shadow-stack-v7-0-a9532eebfb1d@kernel.org
Changes in v7:
- Rebase onto v6.11-rc1.
- Typo fixes.
- Link to v6: https://lore.kernel.org/r/20240623-clone3-shadow-stack-v6-0-9ee7783b1fb9@kernel.org
Changes in v6:
- Rebase onto v6.10-rc3.
- Ensure we don't try to free the parent shadow stack in error paths of
x86 arch code.
- Spelling fixes in userspace API document.
- Additional cleanups and improvements to the clone3() tests to support
the shadow stack tests.
- Link to v5: https://lore.kernel.org/r/20240203-clone3-shadow-stack-v5-0-322c69598e4b@kernel.org
Changes in v5:
- Rebase onto v6.8-rc2.
- Rework ABI to have the user allocate the shadow stack memory with
map_shadow_stack() and a token.
- Force inlining of the x86 shadow stack enablement.
- Move shadow stack enablement out into a shared header for reuse by
other tests.
- Link to v4: https://lore.kernel.org/r/20231128-clone3-shadow-stack-v4-0-8b28ffe4f676@kernel.org
Changes in v4:
- Formatting changes.
- Use a define for minimum shadow stack size and move some basic
validation to fork.c.
- Link to v3: https://lore.kernel.org/r/20231120-clone3-shadow-stack-v3-0-a7b8ed3e2acc@kernel.org
Changes in v3:
- Rebase onto v6.7-rc2.
- Remove stale shadow_stack in internal kargs.
- If a shadow stack is specified unconditionally use it regardless of
CLONE_ parameters.
- Force enable shadow stacks in the selftest.
- Update changelogs for RISC-V feature rename.
- Link to v2: https://lore.kernel.org/r/20231114-clone3-shadow-stack-v2-0-b613f8681155@kernel.org
Changes in v2:
- Rebase onto v6.7-rc1.
- Remove ability to provide preallocated shadow stack, just specify the
desired size.
- Link to v1: https://lore.kernel.org/r/20231023-clone3-shadow-stack-v1-0-d867d0b5d4d0@kernel.org
---
Mark Brown (8):
arm64/gcs: Return a success value from gcs_alloc_thread_stack()
Documentation: userspace-api: Add shadow stack API documentation
selftests: Provide helper header for shadow stack testing
fork: Add shadow stack support to clone3()
selftests/clone3: Remove redundant flushes of output streams
selftests/clone3: Factor more of main loop into test_clone3()
selftests/clone3: Allow tests to flag if -E2BIG is a valid error code
selftests/clone3: Test shadow stack support
Documentation/userspace-api/index.rst | 1 +
Documentation/userspace-api/shadow_stack.rst | 44 +++++
arch/arm64/include/asm/gcs.h | 8 +-
arch/arm64/kernel/process.c | 8 +-
arch/arm64/mm/gcs.c | 55 +++++-
arch/x86/include/asm/shstk.h | 11 +-
arch/x86/kernel/process.c | 2 +-
arch/x86/kernel/shstk.c | 53 ++++-
include/asm-generic/cacheflush.h | 11 ++
include/linux/sched/task.h | 17 ++
include/uapi/linux/sched.h | 9 +-
kernel/fork.c | 93 +++++++--
tools/testing/selftests/clone3/clone3.c | 226 ++++++++++++++++++----
tools/testing/selftests/clone3/clone3_selftests.h | 65 ++++++-
tools/testing/selftests/ksft_shstk.h | 98 ++++++++++
15 files changed, 620 insertions(+), 81 deletions(-)
---
base-commit: 76cea30ad520238160bf8f5e2f2803fcd7a08d22
change-id: 20231019-clone3-shadow-stack-15d40d2bf536
Best regards,
--
Mark Brown <broonie@kernel.org>
^ permalink raw reply
* Re: [PATCH RESEND 17/62] doc: modernize Documentation/filesystems/ramfs-rootfs-initramfs.rst
From: Rob Landley @ 2025-09-15 21:05 UTC (permalink / raw)
To: Askar Safin, linux-fsdevel, linux-kernel
Cc: Linus Torvalds, Greg Kroah-Hartman, Christian Brauner, Al Viro,
Jan Kara, Christoph Hellwig, Jens Axboe, Andy Shevchenko,
Aleksa Sarai, Thomas Weißschuh, Julian Stecklina, Gao Xiang,
Art Nikpal, Andrew Morton, Eric Curtin, Alexander Graf,
Lennart Poettering, linux-arch, linux-alpha, linux-snps-arc,
linux-arm-kernel, linux-csky, linux-hexagon, loongarch,
linux-m68k, linux-mips, linux-openrisc, linux-parisc,
linuxppc-dev, linux-riscv, linux-s390, linux-sh, sparclinux,
linux-um, x86, Ingo Molnar, linux-block, initramfs, linux-api,
linux-doc, linux-efi, linux-ext4, Theodore Y . Ts'o,
linux-acpi, Michal Simek, devicetree, Luis Chamberlain, Kees Cook,
Thorsten Blum, Heiko Carstens, patches
In-Reply-To: <20250913003842.41944-18-safinaskar@gmail.com>
On 9/12/25 19:37, Askar Safin wrote:
> Update it to reflect initrd removal.
>
> Also I specified that error reports should
> go to linux-doc@vger.kernel.org , because
> Rob Landley said that he keeps getting
> reports about this document and is unable
> to fix them
Do you think emailing a list I could forward stuff to will improve matters?
I find the community an elaborate bureaucracy unresponsive to hobbyists.
Documentation/process/submitting-patches.rst being a 934 line document
with a bibliography, plus a 24 step checklist not counting the a) b) c)
subsections are just symptoms. The real problem is following those is
not sufficient to navigate said bureaucracy.
> What is ramfs?
> --------------
>
> @@ -101,9 +103,9 @@ archive is extracted into it, the kernel will fall through to the older code
> to locate and mount a root partition, then exec some variant of /sbin/init
> out of that.
>
> -All this differs from the old initrd in several ways:
> +All this differs from the old initrd (removed in 2025) in several ways:
Why keep the section when you removed the old mechanism? You took away
their choices, you don't need to sell them on it.
(Unless you're trying to sell them on using a current linux kernel
rather than 2.6 or bsd or qnx or something. But if they _do_ remove 32
bit support, or stick a rust dependency in the base build, I suspect
that ship has sailed...)
> - - The old initrd was always a separate file, while the initramfs archive is
> + - The old initrd was always a separate file, while the initramfs archive can be
> linked into the linux kernel image. (The directory ``linux-*/usr`` is
> devoted to generating this archive during the build.)
>
> @@ -137,7 +139,7 @@ Populating initramfs:
>
> The 2.6 kernel build process always creates a gzipped cpio format initramfs
> archive and links it into the resulting kernel binary. By default, this
> -archive is empty (consuming 134 bytes on x86).
> +archive is nearly empty (consuming 134 bytes on x86).
Those two lines you just touched contradict each other.
For historical reference, commit c33df4eaaf41 in 2007 added a second
codepath to special case NOT having an initramfs, for some reason.
That's how static linked cpio in the kernel image and external initrd=
loaded cpio from the bootloader wound up having different behavior.
The init/noinitramfs.c file does init/mkdir("/dev") and
init_mknod("/dev/console") because calling the syscall_blah() functions
directly was considered icky so they created gratuitous wrappers to do
it for you instead, because that's cleaner somehow. (Presumably the same
logic as C++ having get and set methods that perform a simple assignment
and return a value. Because YOU can't be trusted to touch MY code.)
Note that ONLY init/noinitramfs.c creates /dev/console. You'd THINK the
logical thing to do would be to detect failure of the filp_open() in
console_on_rootfs() and do the mkdir/mknod there and retry (since that's
__init code too), but no...
My VERY vague recollection from back in the dark ages is if you didn't
specify any INITRAMFS_SOURCE in kconfig then gen_init_cpio got called
with no arguments and spit out a "usage" section that got interpreted as
scripts/gen_initramfs_list.sh output, back when the plumbing ignored
lines it didn't understand but there was an "example: a simple
initramfs" section in the usage with "dir /dev" and "nod /dev/console"
lines that created a cpio archive with /dev/console in it which would
get statically linked in as a "default", and code reached out and used
this because it was there without understanding WHY it was there. So it
initially worked by coincidence, and rather than make it explicit they
went "two codepaths, half the testing!" and thus...
Anyway, that's why the 130+ byte archive was there. It wasn't actually
empty, even when initramfs was disabled.
One of the "cleanups that didn't actually fix it" was
https://github.com/mpe/linux-fullhistory/commit/2bd3a997befc if you want
to dig into the history yourself. I wrote my docs in 2005 and that was
2010 so "somewhere in there"...
> -If the kernel has initrd support enabled, an external cpio.gz archive can also
> -be passed into a 2.6 kernel in place of an initrd. In this case, the kernel
> -will autodetect the type (initramfs, not initrd) and extract the external cpio
> +If the kernel has CONFIG_BLK_DEV_INITRD enabled, an external cpio.gz archive can also
You renamed that symbol, then even you use the old name here.
> +be passed into a 2.6 kernel. In this case, the kernel will extract the external cpio
> archive into rootfs before trying to run /init.
>
> -This has the memory efficiency advantages of initramfs (no ramdisk block
> -device) but the separate packaging of initrd (which is nice if you have
> +This is nice if you have
> non-GPL code you'd like to run from initramfs, without conflating it with
> -the GPL licensed Linux kernel binary).
> +the GPL licensed Linux kernel binary.
IANAL: Whether or not this qualifies as "mere aggregation" had yet to go
to court last I heard.
Which is basically why
https://hackmd.io/@starnight/Load_Firmware_Files_Later_in_Linux_Kernel
was so screwed up in the first place: the logical thing to do would be
put the firmware in a static initramfs and have the module
initialization happen after initramfs was populated... BUT LICENSING! We
must have a much more complicated implementation because license. I
believe I suggested passing said initramfs in via the initrd mechanism
so it remains a separate file until boot time, and was ignored. *shrug*
The usual...
> It can also be used to supplement the kernel's built-in initramfs image. The
> files in the external archive will overwrite any conflicting files in
> @@ -278,7 +278,7 @@ User Mode Linux, like so::
> EOF
> gcc -static hello.c -o init
> echo init | cpio -o -H newc | gzip > test.cpio.gz
> - # Testing external initramfs using the initrd loading mechanism.
> + # Testing external initramfs.
Does grub not still call it "initrd"?
> qemu -kernel /boot/vmlinuz -initrd test.cpio.gz /dev/zero
A) they added -hda so you don't have to give it a dummy /dev/zero anymore.
B) there's no longer a "qemu" defaulting to the current architecture,
you have to explicitly specify qemu-system-blah unless you create the
symlink yourself by hand. This was considered an "improvement" by IBM
bureaucrats. (Not a regression, a "feature". Oh well...)
C) to be honest I'd just point people at mkroot for examples these days,
but I'm biased. (It smells like me.)
Rob
^ permalink raw reply
* Re: [PATCH 00/62] initrd: remove classic initrd support
From: Rob Landley @ 2025-09-15 16:43 UTC (permalink / raw)
To: Askar Safin, linux-fsdevel, linux-kernel
Cc: Linus Torvalds, Greg Kroah-Hartman, Christian Brauner, Al Viro,
Jan Kara, Christoph Hellwig, Jens Axboe, Andy Shevchenko,
Aleksa Sarai, Thomas Weißschuh, Julian Stecklina, Gao Xiang,
Art Nikpal, Andrew Morton, Eric Curtin, Alexander Graf,
Lennart Poettering, linux-arch, linux-alpha, linux-snps-arc,
linux-arm-kernel, linux-csky, linux-hexagon, loongarch,
linux-m68k, linux-mips, linux-openrisc, linux-parisc,
linuxppc-dev, linux-riscv, linux-s390, linux-sh, sparclinux,
linux-um, x86, Ingo Molnar, linux-block, initramfs, linux-api,
linux-doc, linux-efi, linux-ext4, Theodore Y . Ts'o,
linux-acpi, Michal Simek, devicetree, Luis Chamberlain, Kees Cook,
Thorsten Blum, Heiko Carstens, patches
In-Reply-To: <20250912223937.3735076-1-safinaskar@zohomail.com>
On 9/12/25 17:38, Askar Safin wrote:
> Intro
> ====
> This patchset removes classic initrd (initial RAM disk) support,
> which was deprecated in 2020.
Still useful for embedded systems that can memory map flash, but it's
getting harder to find embedded developers who consider new kernels an
improvement over older ones...
> Initramfs still stays, and RAM disk itself (brd) still stays, too.
While you're at it, could you fix static/builtin initramfs so PID 1 has
a valid stdin/stdout/stderr?
A static initramfs won't create /dev/console if the embedded initramfs
image doesn't contain it, which a non-root build can't mknod, so the
kernel plumbing won't see it dev in the directory we point it at unless
we build with root access. This means the open("/dev/console") fails, so
init starts with no error reporting and we have to get far enough to
mount our own devtmpfs or similar and open our own stdout/stderr before
we can see any error output from init, which is kinda brittle.
I posted various patches to make CONFIG_DEVTMPFS_MOUNT work for initmpfs
repeatedly since 2017, which also addressed it, but the kernel
community's been hermetically sealed against outside intrusion for a
while now...
https://lkml.iu.edu/hypermail/linux/kernel/2005.1/09399.html
https://lkml.iu.edu/2302.2/05597.html
> init/do_mounts* and init/*initramfs* are listed in VFS entry in
> MAINTAINERS, so I think this patchset should go through VFS tree.
> This patchset touchs every subdirectory in arch/, so I tested it
> on 8 (!!!) archs in Qemu (see details below).
Oh hey, somebody using mkroot. Cool. :)
My current "passes basic automated smoketests" list for 6.16 is:
aarch64 armv4l armv5l armv7l i486 i686 m68k mips64 mipsel mips powerpc
powerpc64le powerpc64 riscv32 riscv64 s390x sh4 x86_64
I'm assuming that's your 8: arm, x86, m68k, mips, ppc, riscv, s390x,
superh. (The variants are mostly 32/64 bit and bit/little endian, couple
architecture generations in there. The old ones go out of patent first,
you can always tell patents are about to expire and get generic clones
when corporate shills start insisting that support for something REALLY
NEEDS TO GO AWAY RIGHT NOW...)
The or1k, microblaze, and sh4eb targets mostly work: sh4eb has broken
eithernet (never tracked down whether it's kernel or qemu that's wrong I
just know they disagree), or1k doesn't know how to exit ala
https://lists.gnu.org/archive/html/qemu-devel/2024-11/msg04522.html and
microblaze never wired up -hda to their hard drive emulation
https://lists.nongnu.org/archive/html/qemu-devel/2025-01/msg01149.html
but I haven't had the spoons to argue with IBM Hat developers about
procedure compliance auditing.
I need to track down a decent qemu emulation for armv7m, last time I
tried with vanilla was https://landley.net/notes-2023.html#23-02-2023
which was not promising, I downloaded a pic32 qemu fork last week, but
haven't had the spoons to follow up on that either. Or to ship a new
toybox/mkroot release: I've had 6.16 kernel patches since the week it
came out, unbreaking powerpc and adding fdpic support to sh4-mmu, but
hobbyist friendly this community ain't. Sigh, I should get back on the
(beating a dead) horse...
I had hexagon userspace working for a while ("qemu-hexagon ls -l") but
no kernel for it: Taylor Simpson said he was going to post a
qemu-system-hexagon patchset with a comet board emulation, but that
architecture has no gcc support (there was a gcc fork on code aurora but
they abandoned it when the FSF went gplv3) so it needs an llvm-only
toolchain build with a non-vanilla musl libc fork... Honestly the
problem is compiler-rt sucks rocks: I should cycle back around to
https://landley.net/notes-2021.html#28-07-2021 but just haven't.
(Although part of the "Just haven't" is that I posted a patch to lkml
making generic $CROSS_COMPILE prefixes automatically work whether your
toolchain was gcc or llvm, and the response was literally "we decided to
manually specify LLVM= on the command line so you must always do that
and we're refusing your two line fix to NOT need to do that". No really:
https://lkml.iu.edu/2302.2/08170.html
> Warning: this patchset renames CONFIG_BLK_DEV_INITRD (!!!) to CONFIG_INITRAMFS
> and CONFIG_RD_* to CONFIG_INITRAMFS_DECOMPRESS_* (for example,
> CONFIG_RD_GZIP to CONFIG_INITRAMFS_DECOMPRESS_GZIP).
> If you still use initrd, see below for workaround.
Which will break existing configs for what benefit?
I'm not convinced the churn improves matters. Presumably the kernel
command line paremeter is still rdinit= and grub still uses the "initrd"
command to load an external cpio.gz.
But I bisect to find breakage like that every release so I assume the
other embedded linux developers... are mostly shipping 10+ year old
kernels that use half the memory of today's.
> Details
> ====
> I not only removed initrd, I also removed a lot of code, which
> became dead, including a lot of code in arch/.
>
> Still I think the only two architectures I touched in non-trivial
> way are sh and 32-bit arm.
>
> Also I renamed some files, functions and variables (which became misnomers) to proper names,
> moved some code around, removed a lot of mentions of initrd
> in code and comments. Also I cleaned up some docs.
Now that lkml.iu.edu is back up (yay!) all the links in
ramfs-rootfs-initramfs.txt can theoretically be fixed just by switching
the domain name.
> For example, I renamed the following global variables:
>
> __initramfs_start
> __initramfs_size
That already said initramfs, and you renamed it.
> phys_initrd_start
> phys_initrd_size
> initrd_start
> initrd_end
Which is data delivered through grub's "initrd" command. Here's how I've
been explaining it to people for years:
1) initrd is the external blob from the bootloader's initrd= option.
2) initramfs is the extractor plumbing, _init code that gets discarded.
3) rootfs is (for some reason) the name of the mounted filesystem in
/proc/mounts (because letting it say "ramfs" or "tmpfs" like normal in
/proc/mounts would be consistent and immediately understandable, so they
couldn't have that).
(No I don't know why it's called rootfs. Having things like df not show
overmounted filesystems isn't special case logic, why...? The argument
to special case this because you can't unmount it is like saying PID 1
shouldn't have a number because it can't exit. I would happily call the
whole thing initramfs... but it's already not.)
> to:
>
> __builtin_initramfs_start
> __builtin_initramfs_size
> phys_external_initramfs_start
> phys_external_initramfs_size
> virt_external_initramfs_start
> virt_external_initramfs_end
Do you believe people will understand what the slightly longer names are
without looking them up?
I'm all for removing obsolete code, but a partial cleanup that still
leaves various sharp edges around isn't necessarily a net improvement.
Did you remove the NFS mount code from init/do_mounts.c? Part of the
initramfs justification back in 2005 was "you can have a tiny initramfs
set up our root filesystem so most of the init special casing can go"...
and then they added CONFIG_DEVTMPFS_MOUNT but made it ONLY apply to the
fallback root after the system has decided NOT to stay on rootfs, and
ignored my patches to at least make it consistent.
The one config symbol that really seems to bite people in this area is
BLK_DEV_INITRD because a common thing people running from initramfs want
to do is yank the block layer entirely (CONFIG_BLOCK=n) and use
initramfs instead, and needing to enable CONFIG_BLK_DEV_INITRD while
And the INSANE part is they generally want a static initrd to do it so
they're not using the external loader, but Kconfig has INITRAMFS_SOURCE
under CONFIG_BLK_DEV_INITRD and it's a mess. Renaming THAT symbol would
be good.
But then, CONFIG_BLOCK is hidden under CONFIG_EXPERT which selects
DEBUG_KERNEL (INCREASING KERNEL SIZE!!!) and thus everybody who does
this patches the kconfig plumbing to be less stupid anyway. So the
problem isn't JUST renaming the symbol...
(Oh CONFIG_EXPERT is SO STUPID. It's got a menu under it, but
CONFIG_BLOCK isn't in that menu, it's at the top of menuconfig between
loadable module support and executable file formats, just invisible
unless you go down into a menu and switch on a setting and then back out
to go find it. WHY WOULD YOU DO THAT?)
> New names precisely capture meaning of these variables.
To you. I'm not entirely sure what virt_external means. (Yes I could go
read the code. No I don't want to. I EXPECT to need context and
refreshing stuff, but having it change out from under me since the LAST
time I did that is annoying when it's "same thing, new name, because".)
It makes more sense to YOU because you changed it to smell like you.
Meanwhile 35 years of installed base expertise in other people's heads
has been discarded and developed version skew for anyone maintaining an
existing system. (That's not a "never do this", that's a "be aware
humans consistently have the wrong weightings in our heads for this".)
Personally I usually have to look it up either way. And am spending more
and more of my time poking at older kernels rather because newer stuff
has either removed support for things I need or grown dependencies. (And
because there's 20 years of installed base still in various stages of
use, I'm personally likely to spend more time looking at the old names
than the new ones.)
> This will break all configs out there (update your configs!).
> Still I think this is okay,
Because you don't have to clean up after it.
> because config names never were part of stable API.
I can forward everyone who asks me questions to you, or just agree when
they tell me it's yet another reason not to upgrade.
> Other user-visible changes:
>
> - Removed kernel command line parameters "load_ramdisk" and
> "prompt_ramdisk", which did nothing and were deprecated
Sure.
> - Removed kernel command line parameter "ramdisk_start",
> which was used for initrd only (not for initramfs)
Some bootloaders appended that to the kernel command line to specify
where in memory they've loaded the initrd image, which could be a
cpio.gz once upon a time. No idea what regressions happened since though.
(Last new bootloader I was involved with that had to make it work used
some horrible hack editing a dtb at a fixed offset, like the old "rdev"
trick but more brittle. Because "device tree better" than human readable
textual mechanism. Fixing ramdisk_start to work right sounded like a
more sane approach to me, but...)
> I tested my patchset on many architectures in Qemu using my Rust
> program, heavily based on mkroot [1].
You rewrote a 400 line bash script in rust.
Yeah, that's a rust developer. (And it smells like you now...)
> I used the following cross-compilers:
>
> aarch64-linux-musleabi
> armv4l-linux-musleabihf
> armv5l-linux-musleabihf
> armv7l-linux-musleabihf
> i486-linux-musl
> i686-linux-musl
> mips-linux-musl
> mips64-linux-musl
> mipsel-linux-musl
> powerpc-linux-musl
> powerpc64-linux-musl
> powerpc64le-linux-musl
> riscv32-linux-musl
> riscv64-linux-musl
> s390x-linux-musl
> sh4-linux-musl
> sh4eb-linux-musl
> x86_64-linux-musl
or1k and microblaze work, they just don't pass the full smoketest for
reasons that shouldn't affect initramfs testing.
I'm still waiting for Rich to ship the next musl release to do new
toolchains...
https://www.openwall.com/lists/musl/2025/08/04/1
> Workaround
> ====
> If "retain_initrd" is passed to kernel, then initramfs/initrd,
> passed by bootloader, is retained and becomes available after boot
> as read-only magic file /sys/firmware/initrd [3].
Common use case for eg romfs is memory mapped flash or rom, so the
address range in question isn't actually ram anyway. Mostly on mmu
systems you just don't want the mapping to go away, so the kernel can
still reach out and read it.
> This is even better than classic initrd, because:
> - You can use fs not supported by classic initrd, for example erofs
Network block device was the most recent one I saw used, but it had a
tiny initramfs to set up and switch_root into it...
(Network block device != network filesystem. I have a todo item to
integrate nbd-server into mkroot/testroot.sh but "-hda works" is one of
the things it's testing...)
> - One copy is involved (from /sys/firmware/initrd to some file in /)
> as opposed to two when using classic initrd
Embedded developers have always been reaching out and using mappable
flash directly. Vitaly Wool's ELC talk in 2015 (about running Linux in
256k of sram, yes one quarter of one megabyte) described the process:
https://elinux.org/images/9/90/Linux_for_Microcontrollers-_From_Marginal_to_Mainstream.pdf
Rob
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