* [PATCH v7 01/14] fs: add atomic write unit max opt to statx
From: John Garry @ 2025-04-15 12:14 UTC (permalink / raw)
To: brauner, djwong, hch, viro, jack, cem
Cc: linux-fsdevel, dchinner, linux-xfs, linux-kernel, ojaswin,
ritesh.list, martin.petersen, linux-ext4, linux-block,
catherine.hoang, linux-api, John Garry
In-Reply-To: <20250415121425.4146847-1-john.g.garry@oracle.com>
XFS will be able to support large atomic writes (atomic write > 1x block)
in future. This will be achieved by using different operating methods,
depending on the size of the write.
Specifically a new method of operation based in FS atomic extent remapping
will be supported in addition to the current HW offload-based method.
The FS method will generally be appreciably slower performing than the
HW-offload method. However the FS method will be typically able to
contribute to achieving a larger atomic write unit max limit.
XFS will support a hybrid mode, where HW offload method will be used when
possible, i.e. HW offload is used when the length of the write is
supported, and for other times FS-based atomic writes will be used.
As such, there is an atomic write length at which the user may experience
appreciably slower performance.
Advertise this limit in a new statx field, stx_atomic_write_unit_max_opt.
When zero, it means that there is no such performance boundary.
Masks STATX{_ATTR}_WRITE_ATOMIC can be used to get this new field. This is
ok for older kernels which don't support this new field, as they would
report 0 in this field (from zeroing in cp_statx()) already. Furthermore
those older kernels don't support large atomic writes - apart from block
fops, but there would be consistent performance there for atomic writes
in range [unit min, unit max].
Signed-off-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
block/bdev.c | 3 ++-
fs/ext4/inode.c | 2 +-
fs/stat.c | 6 +++++-
fs/xfs/xfs_iops.c | 2 +-
include/linux/fs.h | 3 ++-
include/linux/stat.h | 1 +
include/uapi/linux/stat.h | 8 ++++++--
7 files changed, 18 insertions(+), 7 deletions(-)
diff --git a/block/bdev.c b/block/bdev.c
index 4844d1e27b6f..b4afc1763e8e 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -1301,7 +1301,8 @@ void bdev_statx(struct path *path, struct kstat *stat,
generic_fill_statx_atomic_writes(stat,
queue_atomic_write_unit_min_bytes(bd_queue),
- queue_atomic_write_unit_max_bytes(bd_queue));
+ queue_atomic_write_unit_max_bytes(bd_queue),
+ 0);
}
stat->blksize = bdev_io_min(bdev);
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 94c7d2d828a6..cdf01e60fa6d 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5692,7 +5692,7 @@ int ext4_getattr(struct mnt_idmap *idmap, const struct path *path,
awu_max = sbi->s_awu_max;
}
- generic_fill_statx_atomic_writes(stat, awu_min, awu_max);
+ generic_fill_statx_atomic_writes(stat, awu_min, awu_max, 0);
}
flags = ei->i_flags & EXT4_FL_USER_VISIBLE;
diff --git a/fs/stat.c b/fs/stat.c
index f13308bfdc98..c41855f62d22 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -136,13 +136,15 @@ EXPORT_SYMBOL(generic_fill_statx_attr);
* @stat: Where to fill in the attribute flags
* @unit_min: Minimum supported atomic write length in bytes
* @unit_max: Maximum supported atomic write length in bytes
+ * @unit_max_opt: Optimised maximum supported atomic write length in bytes
*
* Fill in the STATX{_ATTR}_WRITE_ATOMIC flags in the kstat structure from
* atomic write unit_min and unit_max values.
*/
void generic_fill_statx_atomic_writes(struct kstat *stat,
unsigned int unit_min,
- unsigned int unit_max)
+ unsigned int unit_max,
+ unsigned int unit_max_opt)
{
/* Confirm that the request type is known */
stat->result_mask |= STATX_WRITE_ATOMIC;
@@ -153,6 +155,7 @@ void generic_fill_statx_atomic_writes(struct kstat *stat,
if (unit_min) {
stat->atomic_write_unit_min = unit_min;
stat->atomic_write_unit_max = unit_max;
+ stat->atomic_write_unit_max_opt = unit_max_opt;
/* Initially only allow 1x segment */
stat->atomic_write_segments_max = 1;
@@ -732,6 +735,7 @@ cp_statx(const struct kstat *stat, struct statx __user *buffer)
tmp.stx_atomic_write_unit_min = stat->atomic_write_unit_min;
tmp.stx_atomic_write_unit_max = stat->atomic_write_unit_max;
tmp.stx_atomic_write_segments_max = stat->atomic_write_segments_max;
+ tmp.stx_atomic_write_unit_max_opt = stat->atomic_write_unit_max_opt;
return copy_to_user(buffer, &tmp, sizeof(tmp)) ? -EFAULT : 0;
}
diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index 756bd3ca8e00..f0e5d83195df 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -610,7 +610,7 @@ xfs_report_atomic_write(
if (xfs_inode_can_atomicwrite(ip))
unit_min = unit_max = ip->i_mount->m_sb.sb_blocksize;
- generic_fill_statx_atomic_writes(stat, unit_min, unit_max);
+ generic_fill_statx_atomic_writes(stat, unit_min, unit_max, 0);
}
STATIC int
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 016b0fe1536e..7b19d8f99aff 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3475,7 +3475,8 @@ void generic_fillattr(struct mnt_idmap *, u32, struct inode *, struct kstat *);
void generic_fill_statx_attr(struct inode *inode, struct kstat *stat);
void generic_fill_statx_atomic_writes(struct kstat *stat,
unsigned int unit_min,
- unsigned int unit_max);
+ unsigned int unit_max,
+ unsigned int unit_max_opt);
extern int vfs_getattr_nosec(const struct path *, struct kstat *, u32, unsigned int);
extern int vfs_getattr(const struct path *, struct kstat *, u32, unsigned int);
void __inode_add_bytes(struct inode *inode, loff_t bytes);
diff --git a/include/linux/stat.h b/include/linux/stat.h
index be7496a6a0dd..e3d00e7bb26d 100644
--- a/include/linux/stat.h
+++ b/include/linux/stat.h
@@ -57,6 +57,7 @@ struct kstat {
u32 dio_read_offset_align;
u32 atomic_write_unit_min;
u32 atomic_write_unit_max;
+ u32 atomic_write_unit_max_opt;
u32 atomic_write_segments_max;
};
diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
index f78ee3670dd5..1686861aae20 100644
--- a/include/uapi/linux/stat.h
+++ b/include/uapi/linux/stat.h
@@ -182,8 +182,12 @@ struct statx {
/* File offset alignment for direct I/O reads */
__u32 stx_dio_read_offset_align;
- /* 0xb8 */
- __u64 __spare3[9]; /* Spare space for future expansion */
+ /* Optimised max atomic write unit in bytes */
+ __u32 stx_atomic_write_unit_max_opt;
+ __u32 __spare2[1];
+
+ /* 0xc0 */
+ __u64 __spare3[8]; /* Spare space for future expansion */
/* 0x100 */
};
--
2.31.1
^ permalink raw reply related
* [PATCH v7 00/14] large atomic writes for xfs
From: John Garry @ 2025-04-15 12:14 UTC (permalink / raw)
To: brauner, djwong, hch, viro, jack, cem
Cc: linux-fsdevel, dchinner, linux-xfs, linux-kernel, ojaswin,
ritesh.list, martin.petersen, linux-ext4, linux-block,
catherine.hoang, linux-api, John Garry
Currently atomic write support for xfs is limited to writing a single
block as we have no way to guarantee alignment and that the write covers
a single extent.
This series introduces a method to issue atomic writes via a
software-based method.
The software-based method is used as a fallback for when attempting to
issue an atomic write over misaligned or multiple extents.
For xfs, this support is based on reflink CoW support.
The basic idea of this CoW method is to alloc a range in the CoW fork,
write the data, and atomically update the mapping.
Initial mysql performance testing has shown this method to perform ok.
However, there we are only using 16K atomic writes (and 4K block size),
so typically - and thankfully - this software fallback method won't be
used often.
For other FSes which want large atomics writes and don't support CoW, I
think that they can follow the example in [0].
Catherine is currently working on further xfstests for this feature,
which we hope to share soon.
Based on 8ffd015db85f (tag: v6.15-rc2, xfs/xfs-6.16-merge,
xfs/xfs-6.15-fixes, xfs/for-next) Linux 6.15-rc2
[0] https://lore.kernel.org/linux-xfs/20250310183946.932054-1-john.g.garry@oracle.com/
Differences to v6:
- log item sizes updates (Darrick)
- rtvol support (Darrick)
- mount option for atomic writes (Darrick)
- Add RB tags from Darrick and Christoph (Thanks!)
Differences to v5:
- Add statx unit_max_opt (Christoph, me)
- Add xfs_atomic_write_cow_iomap_begin() (Christoph)
- drop old mechanical changes
- limit atomic write max according to CoW-based atomic write max (Christoph)
- Add xfs_compute_atomic_write_unit_max()
- this contains changes for limiting awu max according to max
transaction log items (Darrick)
- use -ENOPROTOOPT for fallback (Christoph)
- rename xfs_inode_can_atomicwrite() -> xfs_inode_can_hw_atomicwrite()
- rework varoious code comments (Christoph)
- limit CoW-based atomic write to log size and add helpers (Darrick)
- drop IOMAP_DIO_FORCE_WAIT usage in xfs_file_dio_write_atomic()
- Add RB tags from Christoph (thanks!)
Darrick J. Wong (3):
xfs: add helpers to compute log item overhead
xfs: add helpers to compute transaction reservation for finishing
intent items
xfs: allow sysadmins to specify a maximum atomic write limit at mount
time
John Garry (11):
fs: add atomic write unit max opt to statx
xfs: rename xfs_inode_can_atomicwrite() ->
xfs_inode_can_hw_atomicwrite()
xfs: allow block allocator to take an alignment hint
xfs: refactor xfs_reflink_end_cow_extent()
xfs: refine atomic write size check in xfs_file_write_iter()
xfs: add xfs_atomic_write_cow_iomap_begin()
xfs: add large atomic writes checks in xfs_direct_write_iomap_begin()
xfs: commit CoW-based atomic writes atomically
xfs: add xfs_file_dio_write_atomic()
xfs: add xfs_compute_atomic_write_unit_max()
xfs: update atomic write limits
Documentation/admin-guide/xfs.rst | 8 +
block/bdev.c | 3 +-
fs/ext4/inode.c | 2 +-
fs/stat.c | 6 +-
fs/xfs/libxfs/xfs_bmap.c | 5 +
fs/xfs/libxfs/xfs_bmap.h | 6 +-
fs/xfs/libxfs/xfs_trans_resv.c | 315 +++++++++++++++++++++++++++---
fs/xfs/libxfs/xfs_trans_resv.h | 22 +++
fs/xfs/xfs_bmap_item.c | 10 +
fs/xfs/xfs_bmap_item.h | 3 +
fs/xfs/xfs_buf_item.c | 19 ++
fs/xfs/xfs_buf_item.h | 3 +
fs/xfs/xfs_extfree_item.c | 10 +
fs/xfs/xfs_extfree_item.h | 3 +
fs/xfs/xfs_file.c | 87 ++++++++-
fs/xfs/xfs_inode.h | 2 +-
fs/xfs/xfs_iomap.c | 191 +++++++++++++++++-
fs/xfs/xfs_iomap.h | 1 +
fs/xfs/xfs_iops.c | 77 +++++++-
fs/xfs/xfs_iops.h | 3 +
fs/xfs/xfs_log_cil.c | 4 +-
fs/xfs/xfs_log_priv.h | 13 ++
fs/xfs/xfs_mount.c | 86 ++++++++
fs/xfs/xfs_mount.h | 11 ++
fs/xfs/xfs_refcount_item.c | 10 +
fs/xfs/xfs_refcount_item.h | 3 +
fs/xfs/xfs_reflink.c | 143 +++++++++++---
fs/xfs/xfs_reflink.h | 6 +
fs/xfs/xfs_rmap_item.c | 10 +
fs/xfs/xfs_rmap_item.h | 3 +
fs/xfs/xfs_super.c | 28 ++-
fs/xfs/xfs_trace.h | 115 +++++++++++
include/linux/fs.h | 3 +-
include/linux/stat.h | 1 +
include/uapi/linux/stat.h | 8 +-
35 files changed, 1130 insertions(+), 90 deletions(-)
--
2.31.1
^ permalink raw reply
* Re: [PATCH RFT v15 4/8] fork: Add shadow stack support to clone3()
From: Edgecombe, Rick P @ 2025-04-14 18:28 UTC (permalink / raw)
To: dietmar.eggemann@arm.com, broonie@kernel.org,
Szabolcs.Nagy@arm.com, brauner@kernel.org,
dave.hansen@linux.intel.com, debug@rivosinc.com, mgorman@suse.de,
vincent.guittot@linaro.org, fweimer@redhat.com, mingo@redhat.com,
rostedt@goodmis.org, hjl.tools@gmail.com, tglx@linutronix.de,
vschneid@redhat.com, shuah@kernel.org, hpa@zytor.com,
peterz@infradead.org, bp@alien8.de, bsegall@google.com,
x86@kernel.org, juri.lelli@redhat.com
Cc: yury.khrustalev@arm.com, linux-kselftest@vger.kernel.org,
linux-api@vger.kernel.org, jannh@google.com,
linux-kernel@vger.kernel.org, catalin.marinas@arm.com,
will@kernel.org, wilco.dijkstra@arm.com, kees@kernel.org
In-Reply-To: <20250408-clone3-shadow-stack-v15-4-3fa245c6e3be@kernel.org>
On Tue, 2025-04-08 at 19:49 +0100, Mark Brown wrote:
> +int arch_shstk_validate_clone(struct task_struct *t,
> + struct vm_area_struct *vma,
> + struct page *page,
> + struct kernel_clone_args *args)
> +{
> + /*
> + * SSP is aligned, so reserved bits and mode bit are a zero, just mark
> + * the token 64-bit.
> + */
> + void *maddr = kmap_local_page(page);
> + int offset;
> + unsigned long addr, ssp;
> + u64 expected;
> +
> + if (!features_enabled(ARCH_SHSTK_SHSTK))
> + return 0;
> +
> + ssp = args->shadow_stack_pointer;
> + addr = ssp - SS_FRAME_SIZE;
> + expected = ssp | BIT(0);
> + offset = offset_in_page(addr);
> +
> + if (!cmpxchg_to_user_page(vma, page, addr, (unsigned long *)(maddr + offset),
> + expected, 0))
> + return -EINVAL;
> + set_page_dirty_lock(page);
> +
> + return 0;
> +}
> +
First of all, sorry for not contributing on this since v9. I've had an unusual
enormous project conflict (TDX) combined with my test HW dieing.
I tested v15 on x86 and saw a couple problems:
1. I think kmap_local_page() is supposed to be paired kunmap_local(). But shstk
is not supported on highmem systems, so let's just use page_address().
2. Some off by one (frame) errors that cause the clone3 test to fail on x86.
Both fixed in the diff below, but in debugging the off-by-one errors I've
realized this implementation wastes a shadow stack frame.
On x86 when that token is consumed normally it would have:
SSP = token_addr + 8
I always assumed the HW token consumption behavior was to try to save a frame on
the shadow stack. Once the token is consumed it is useless. So might as well
reuse the frame for the next push. But the clone3 behavior is different than the
normal token consumption logic. Instead it will have SSP *at* the token, which
will then have the next call push and leave the zero frame as wasted space.
Do we want this? On arm there is SHADOW_STACK_SET_MARKER, which leaves a marker
token. But on clone3 it will also leave behind a zero frame from the CMPXCHGed
token. So if you use SHADOW_STACK_SET_MARKER you get two marker tokens. And on
x86 you will get one one for clone3 but not others, until x86 implements
SHADOW_STACK_SET_MARKER. At which point x86 has to diverge from arm (bad) or
also have the double marker frame.
The below fixes the x86 functionally, but what do you think of the wasted frame?
One fix would be to change shadow_stack_pointer to shadow_stack_token, and then
have each arch consume it in the normal HW way, leaving the new thread with:
SSP = clone_args->shadow_stack_token + 8
diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c
index 056e2c9ec305..2b0f84ae4367 100644
--- a/arch/x86/kernel/shstk.c
+++ b/arch/x86/kernel/shstk.c
@@ -200,20 +200,19 @@ int arch_shstk_validate_clone(struct task_struct *t,
* SSP is aligned, so reserved bits and mode bit are a zero, just mark
* the token 64-bit.
*/
- void *maddr = kmap_local_page(page);
+ void *maddr = page_address(page);
int offset;
- unsigned long addr, ssp;
+ unsigned long ssp;
u64 expected;
if (!features_enabled(ARCH_SHSTK_SHSTK))
return 0;
ssp = args->shadow_stack_pointer;
- addr = ssp - SS_FRAME_SIZE;
- expected = ssp | BIT(0);
- offset = offset_in_page(addr);
+ expected = (ssp + SS_FRAME_SIZE) | BIT(0);
+ offset = offset_in_page(ssp);
- if (!cmpxchg_to_user_page(vma, page, addr, (unsigned long *)(maddr +
offset),
+ if (!cmpxchg_to_user_page(vma, page, ssp, (unsigned long *)(maddr +
offset),
expected, 0))
return -EINVAL;
set_page_dirty_lock(page);
^ permalink raw reply related
* [PATCH RFT v15 8/8] selftests/clone3: Test shadow stack support
From: Mark Brown @ 2025-04-08 18:49 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,
Yury Khrustalev, Wilco Dijkstra, linux-kselftest, linux-api,
Mark Brown, Kees Cook, Shuah Khan
In-Reply-To: <20250408-clone3-shadow-stack-v15-0-3fa245c6e3be@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>
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..316449c013ca 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.shadow_stack_pointer = (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.shadow_stack_pointer = (unsigned long long)p;
+ break;
+ case CLONE3_ARGS_SHADOW_STACK_NORMAL_MEMORY:
+ p = malloc(getpagesize());
+ p += getpagesize() - sizeof(void *);
+ args.shadow_stack_pointer = (unsigned long long)p;
+ break;
+ case CLONE3_ARGS_SHADOW_STACK_NO_TOKEN:
+ p = get_shadow_stack_page(0);
+ p += getpagesize() - sizeof(void *);
+ args.shadow_stack_pointer = (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..f1069fab17ba 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 shadow_stack_pointer;
+#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)
{
--
2.39.5
^ permalink raw reply related
* [PATCH RFT v15 7/8] selftests/clone3: Allow tests to flag if -E2BIG is a valid error code
From: Mark Brown @ 2025-04-08 18:49 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,
Yury Khrustalev, Wilco Dijkstra, linux-kselftest, linux-api,
Mark Brown, Kees Cook, Kees Cook, Shuah Khan
In-Reply-To: <20250408-clone3-shadow-stack-v15-0-3fa245c6e3be@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>
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);
--
2.39.5
^ permalink raw reply related
* [PATCH RFT v15 6/8] selftests/clone3: Factor more of main loop into test_clone3()
From: Mark Brown @ 2025-04-08 18:49 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,
Yury Khrustalev, Wilco Dijkstra, linux-kselftest, linux-api,
Mark Brown, Kees Cook, Kees Cook, Shuah Khan
In-Reply-To: <20250408-clone3-shadow-stack-v15-0-3fa245c6e3be@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>
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();
}
--
2.39.5
^ permalink raw reply related
* [PATCH RFT v15 5/8] selftests/clone3: Remove redundant flushes of output streams
From: Mark Brown @ 2025-04-08 18:49 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,
Yury Khrustalev, Wilco Dijkstra, linux-kselftest, linux-api,
Mark Brown, Kees Cook, Kees Cook, Shuah Khan
In-Reply-To: <20250408-clone3-shadow-stack-v15-0-3fa245c6e3be@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>
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);
}
--
2.39.5
^ permalink raw reply related
* [PATCH RFT v15 4/8] fork: Add shadow stack support to clone3()
From: Mark Brown @ 2025-04-08 18:49 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,
Yury Khrustalev, Wilco Dijkstra, linux-kselftest, linux-api,
Mark Brown, Kees Cook
In-Reply-To: <20250408-clone3-shadow-stack-v15-0-3fa245c6e3be@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 the 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. 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.
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>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
arch/arm64/mm/gcs.c | 54 +++++++++++++++++++++-
arch/x86/include/asm/shstk.h | 11 +++--
arch/x86/kernel/process.c | 2 +-
arch/x86/kernel/shstk.c | 57 +++++++++++++++++++++---
include/asm-generic/cacheflush.h | 11 +++++
include/linux/sched/task.h | 17 +++++++
include/uapi/linux/sched.h | 10 +++--
kernel/fork.c | 96 +++++++++++++++++++++++++++++++++++-----
8 files changed, 232 insertions(+), 26 deletions(-)
diff --git a/arch/arm64/mm/gcs.c b/arch/arm64/mm/gcs.c
index 1f633a482558..10ee92390ea1 100644
--- a/arch/arm64/mm/gcs.c
+++ b/arch/arm64/mm/gcs.c
@@ -43,8 +43,24 @@ int gcs_alloc_thread_stack(struct task_struct *tsk,
{
unsigned long addr, size;
- if (!system_supports_gcs())
+ if (!system_supports_gcs()) {
+ if (args->shadow_stack_pointer)
+ 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->shadow_stack_pointer) {
+ tsk->thread.gcs_base = 0;
+ tsk->thread.gcs_size = 0;
+ tsk->thread.gcspr_el0 = args->shadow_stack_pointer;
return 0;
+ }
if (!task_gcs_el0_enabled(tsk))
return 0;
@@ -68,6 +84,42 @@ 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;
+
+ /* Ensure that a token written as a result of a pivot is visible */
+ gcsb_dsync();
+
+ gcspr_el0 = args->shadow_stack_pointer;
+ if (!gcs_consume_token(vma, page, gcspr_el0))
+ return -EINVAL;
+
+ tsk->thread.gcspr_el0 = gcspr_el0 + sizeof(u64);
+
+ /* Ensure that our token consumption visible */
+ gcsb_dsync();
+
+ 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 ba6f2fe43848..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, unsigned long 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,
- unsigned long 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 962c3ce39323..002b05483c62 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -213,7 +213,7 @@ 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 059685612362..056e2c9ec305 100644
--- a/arch/x86/kernel/shstk.c
+++ b/arch/x86/kernel/shstk.c
@@ -191,18 +191,65 @@ void reset_thread_features(void)
current->thread.features_locked = 0;
}
-unsigned long shstk_alloc_thread_stack(struct task_struct *tsk, unsigned long 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)
+{
+ /*
+ * SSP is aligned, so reserved bits and mode bit are a zero, just mark
+ * the token 64-bit.
+ */
+ void *maddr = kmap_local_page(page);
+ int offset;
+ unsigned long addr, ssp;
+ u64 expected;
+
+ if (!features_enabled(ARCH_SHSTK_SHSTK))
+ return 0;
+
+ ssp = args->shadow_stack_pointer;
+ addr = ssp - SS_FRAME_SIZE;
+ expected = ssp | BIT(0);
+ offset = offset_in_page(addr);
+
+ if (!cmpxchg_to_user_page(vma, page, addr, (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;
+ unsigned long 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->shadow_stack_pointer)
+ 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->shadow_stack_pointer) {
+ shstk->base = 0;
+ shstk->size = 0;
+ return args->shadow_stack_pointer;
+ }
/*
* For CLONE_VFORK the child will share the parents shadow stack.
@@ -222,7 +269,7 @@ unsigned long shstk_alloc_thread_stack(struct task_struct *tsk, unsigned long cl
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 ca1db4b92c32..5d1290f7d9c0 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 shadow_stack_pointer;
};
/*
@@ -237,4 +239,19 @@ 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..586a1c05a4e4 100644
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -84,6 +84,8 @@
* kernel's limit of nested PID namespaces.
* @cgroup: If CLONE_INTO_CGROUP is specified set this to
* a file descriptor for the cgroup.
+ * @shadow_stack_pointer: Value to use for shadow stack pointer in the
+ * child process.
*
* The structure is versioned by size and thus extensible.
* New struct members must go at the end of the struct and
@@ -101,12 +103,14 @@ struct clone_args {
__aligned_u64 set_tid;
__aligned_u64 set_tid_size;
__aligned_u64 cgroup;
+ __aligned_u64 shadow_stack_pointer;
};
#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 c4b26cd8998b..a0427524fec3 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2162,6 +2162,51 @@ static void rv_task_fork(struct task_struct *p)
#define rv_task_fork(p) do {} while (0)
#endif
+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->shadow_stack_pointer)
+ return 0;
+
+ mm = get_task_mm(p);
+ if (!mm)
+ return -EFAULT;
+
+ mmap_read_lock(mm);
+
+ addr = untagged_addr_remote(mm, args->shadow_stack_pointer);
+ 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.
@@ -2436,6 +2481,9 @@ __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;
@@ -3002,7 +3050,9 @@ noinline static 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, shadow_stack_pointer) !=
+ CLONE_ARGS_SIZE_VER3);
+ BUILD_BUG_ON(sizeof(struct clone_args) != CLONE_ARGS_SIZE_VER3);
if (unlikely(usize > PAGE_SIZE))
return -E2BIG;
@@ -3035,16 +3085,17 @@ noinline static 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,
+ .shadow_stack_pointer = args.shadow_stack_pointer,
};
if (args.set_tid &&
@@ -3085,6 +3136,27 @@ 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->shadow_stack_pointer)
+ return true;
+
+ if (!IS_ALIGNED(kargs->shadow_stack_pointer, sizeof(void *)))
+ return false;
+
+ /*
+ * The architecture must check support on the specific
+ * machine.
+ */
+ 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. */
@@ -3107,7 +3179,7 @@ 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;
--
2.39.5
^ permalink raw reply related
* [PATCH RFT v15 3/8] selftests: Provide helper header for shadow stack testing
From: Mark Brown @ 2025-04-08 18:49 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,
Yury Khrustalev, Wilco Dijkstra, linux-kselftest, linux-api,
Mark Brown, Kees Cook, Kees Cook, Shuah Khan
In-Reply-To: <20250408-clone3-shadow-stack-v15-0-3fa245c6e3be@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>
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
--
2.39.5
^ permalink raw reply related
* [PATCH RFT v15 2/8] Documentation: userspace-api: Add shadow stack API documentation
From: Mark Brown @ 2025-04-08 18:49 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,
Yury Khrustalev, Wilco Dijkstra, linux-kselftest, linux-api,
Mark Brown, Kees Cook, Kees Cook, Shuah Khan
In-Reply-To: <20250408-clone3-shadow-stack-v15-0-3fa245c6e3be@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>
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..65c665496624
--- /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
+writeable 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.
--
2.39.5
^ permalink raw reply related
* [PATCH RFT v15 1/8] arm64/gcs: Return a success value from gcs_alloc_thread_stack()
From: Mark Brown @ 2025-04-08 18:49 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,
Yury Khrustalev, Wilco Dijkstra, linux-kselftest, linux-api,
Mark Brown, Kees Cook
In-Reply-To: <20250408-clone3-shadow-stack-v15-0-3fa245c6e3be@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 f50660603ecf..d8923b5f03b7 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 42faebb7b712..45130ea7ea6e 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -297,7 +297,7 @@ 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;
@@ -305,9 +305,9 @@ static int copy_thread_gcs(struct task_struct *p,
p->thread.gcs_base = 0;
p->thread.gcs_size = 0;
- 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;
p->thread.gcs_el0_mode = current->thread.gcs_el0_mode;
p->thread.gcs_el0_locked = current->thread.gcs_el0_locked;
diff --git a/arch/arm64/mm/gcs.c b/arch/arm64/mm/gcs.c
index 5c46ec527b1c..1f633a482558 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)
--
2.39.5
^ permalink raw reply related
* [PATCH RFT v15 0/8] fork: Support shadow stacks in clone3()
From: Mark Brown @ 2025-04-08 18:49 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,
Yury Khrustalev, Wilco Dijkstra, linux-kselftest, linux-api,
Mark Brown, Kees Cook, Kees Cook, Shuah Khan
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.
Please note that the x86 portions of this code are build tested only, I
don't appear to have a system that can run CET available to me.
[1] https://lore.kernel.org/linux-arm-kernel/20241001-arm64-gcs-v13-0-222b78d87eee@kernel.org/T/#mc58f97f27461749ccf400ebabf6f9f937116a86b
Signed-off-by: Mark Brown <broonie@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 | 62 +++++-
arch/x86/include/asm/shstk.h | 11 +-
arch/x86/kernel/process.c | 2 +-
arch/x86/kernel/shstk.c | 57 +++++-
include/asm-generic/cacheflush.h | 11 ++
include/linux/sched/task.h | 17 ++
include/uapi/linux/sched.h | 10 +-
kernel/fork.c | 96 +++++++--
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, 635 insertions(+), 81 deletions(-)
---
base-commit: 0af2f6be1b4281385b618cb86ad946eded089ac8
change-id: 20231019-clone3-shadow-stack-15d40d2bf536
Best regards,
--
Mark Brown <broonie@kernel.org>
^ permalink raw reply
* Re: [PATCH RFC] statx.2: Add stx_atomic_write_unit_max_opt
From: Christoph Hellwig @ 2025-04-07 6:51 UTC (permalink / raw)
To: John Garry
Cc: Christoph Hellwig, alx, brauner, djwong, dchinner, linux-man,
linux-fsdevel, linux-xfs, linux-kernel, ojaswin, ritesh.list,
martin.petersen, linux-api
In-Reply-To: <aab0aa19-f279-42b4-9ab7-0cc6e2fa3b9f@oracle.com>
On Fri, Apr 04, 2025 at 10:23:09AM +0100, John Garry wrote:
>> that optimized case will not involve the usual hardware offload.
>>
>>
> stx_atomic_write_unit_max_opt it is then.
>
> Or stx_atomic_write_unit_max_optimal or stx_atomic_write_unit_max_fast. Or
> similar..
As we've used opt in various other ABIs I'd stick to that.
^ permalink raw reply
* Re: [PATCH RFC] statx.2: Add stx_atomic_write_unit_max_opt
From: John Garry @ 2025-04-04 9:23 UTC (permalink / raw)
To: Christoph Hellwig
Cc: alx, brauner, djwong, dchinner, linux-man, linux-fsdevel,
linux-xfs, linux-kernel, ojaswin, ritesh.list, martin.petersen,
linux-api
In-Reply-To: <20250404090601.GA12163@lst.de>
On 04/04/2025 10:06, Christoph Hellwig wrote:
> On Thu, Apr 03, 2025 at 04:07:04PM +0100, John Garry wrote:
>> So I am thinking one of these:
>> a. stx_atomic_write_unit_max_dev
>> b. stx_atomic_write_unit_max_bdev
>> c. stx_atomic_write_unit_max_align
>> d. stx_atomic_write_unit_max_hw
>>
>> The terms dev (or device) and bdev are already used in the meaning of some
>> members in struct statx, so not too bad. However, when we support large
>> atomic writes for XFS rtvol, the bdev atomic write limit and rtextsize
>> would influence this value (so just bdev might be a bit misleading in the
>> name).
>
> Don't. Especially when you have a natively out of write file system
> that optimized case will not involve the usual hardware offload.
>
>
stx_atomic_write_unit_max_opt it is then.
Or stx_atomic_write_unit_max_optimal or stx_atomic_write_unit_max_fast.
Or similar..
cheers,
John
^ permalink raw reply
* Re: [PATCH RFC] statx.2: Add stx_atomic_write_unit_max_opt
From: Christoph Hellwig @ 2025-04-04 9:06 UTC (permalink / raw)
To: John Garry
Cc: Christoph Hellwig, alx, brauner, djwong, dchinner, linux-man,
linux-fsdevel, linux-xfs, linux-kernel, ojaswin, ritesh.list,
martin.petersen, linux-api
In-Reply-To: <5485c1ad-8a20-40bc-aa75-68b820de5e1c@oracle.com>
On Thu, Apr 03, 2025 at 04:07:04PM +0100, John Garry wrote:
> So I am thinking one of these:
> a. stx_atomic_write_unit_max_dev
> b. stx_atomic_write_unit_max_bdev
> c. stx_atomic_write_unit_max_align
> d. stx_atomic_write_unit_max_hw
>
> The terms dev (or device) and bdev are already used in the meaning of some
> members in struct statx, so not too bad. However, when we support large
> atomic writes for XFS rtvol, the bdev atomic write limit and rtextsize
> would influence this value (so just bdev might be a bit misleading in the
> name).
Don't. Especially when you have a natively out of write file system
that optimized case will not involve the usual hardware offload.
^ permalink raw reply
* Re: [PATCH RFC] statx.2: Add stx_atomic_write_unit_max_opt
From: John Garry @ 2025-04-03 15:07 UTC (permalink / raw)
To: Christoph Hellwig
Cc: alx, brauner, djwong, dchinner, linux-man, linux-fsdevel,
linux-xfs, linux-kernel, ojaswin, ritesh.list, martin.petersen,
linux-api
In-Reply-To: <20250323064029.GA30848@lst.de>
On 23/03/2025 06:40, Christoph Hellwig wrote:
I'm not happy with the name stx_atomic_write_unit_max_opt - it's vague
and subjective.
So I am thinking one of these:
a. stx_atomic_write_unit_max_dev
b. stx_atomic_write_unit_max_bdev
c. stx_atomic_write_unit_max_align
d. stx_atomic_write_unit_max_hw
The terms dev (or device) and bdev are already used in the meaning of
some members in struct statx, so not too bad. However, when we support
large atomic writes for XFS rtvol, the bdev atomic write limit and
rtextsize would influence this value (so just bdev might be a bit
misleading in the name).
As for stx_atomic_write_unit_max_align, it would mean "max
alignment/granularity" for possible HW offload. Not great.
stx_atomic_write_unit_max_hw would match the bdev request queue sysfs
names, but that it a different concept to statx. And it has the same
issue as bdev for rtvol, above.
Any further suggestions or comments?
> On Fri, Mar 21, 2025 at 10:20:21AM +0000, John Garry wrote:
>> Coming back to what was discussed about not adding a new flag to fetch this
>> limit:
>>
>>> Does that actually work? Can userspace assume all unknown statx
>>> fields are padded to zero?
>>
>> In cp_statx, we do pre-zero the statx structure. As such, the rule "if
>> zero, just use hard limit unit max" seems to hold.
>
> Ok, canwe document this somewhere?
>
Sure, but I want to decide on the name first.. if using
stx_atomic_write_unit_max_bdev/_dev/hw, then it would be odd that this
value reports 0 for old kernels (as the bdev limit would never really be 0).
Then if we have rule "stx_atomic_write_unit_max_bdev=0 means that
stx_atomic_write_unit_max_bdev = stx_atomic_write_unit_max", this breaks
for when we solely rely on FS-based atomics, as
stx_atomic_write_unit_max_bdev would be 0 there and that should really
mean 0 (and not stx_atomic_write_unit_max).
So then we should have a new mask to fetch this field, which is not
ideal, but ok.
^ permalink raw reply
* Re: [PATCH v4 0/3] fs: introduce getfsxattrat and setfsxattrat syscalls
From: Amir Goldstein @ 2025-03-28 14:09 UTC (permalink / raw)
To: Pali Rohár
Cc: Andrey Albershteyn, Richard Henderson, Matt Turner, Russell King,
Catalin Marinas, Will Deacon, Geert Uytterhoeven, Michal Simek,
Thomas Bogendoerfer, James E.J. Bottomley, Helge Deller,
Madhavan Srinivasan, Michael Ellerman, Nicholas Piggin,
Christophe Leroy, Naveen N Rao, Heiko Carstens, Vasily Gorbik,
Alexander Gordeev, Christian Borntraeger, Sven Schnelle,
Yoshinori Sato, Rich Felker, John Paul Adrian Glaubitz,
David S. Miller, Andreas Larsson, Andy Lutomirski,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen, x86,
H. Peter Anvin, Chris Zankel, Max Filippov, Alexander Viro,
Christian Brauner, Jan Kara, Mickaël Salaün,
Günther Noack, Arnd Bergmann, Paul Moore, James Morris,
Serge E. Hallyn, linux-alpha, linux-kernel, linux-arm-kernel,
linux-m68k, linux-mips, linux-parisc, linuxppc-dev, linux-s390,
linux-sh, sparclinux, linux-fsdevel, linux-security-module,
linux-api, linux-arch, selinux, Andrey Albershteyn, linux-xfs
In-Reply-To: <20250327211301.kdsohqou3s242coa@pali>
On Thu, Mar 27, 2025 at 10:13 PM Pali Rohár <pali@kernel.org> wrote:
>
> On Thursday 27 March 2025 21:57:34 Amir Goldstein wrote:
> > On Thu, Mar 27, 2025 at 8:26 PM Pali Rohár <pali@kernel.org> wrote:
> > >
> > > On Thursday 27 March 2025 12:47:02 Amir Goldstein wrote:
> > > > On Sun, Mar 23, 2025 at 11:32 AM Pali Rohár <pali@kernel.org> wrote:
> > > > >
> > > > > On Sunday 23 March 2025 09:45:06 Amir Goldstein wrote:
> > > > > > On Fri, Mar 21, 2025 at 8:50 PM Andrey Albershteyn <aalbersh@redhat.com> wrote:
> > > > > > >
> > > > > > > This patchset introduced two new syscalls getfsxattrat() and
> > > > > > > setfsxattrat(). These syscalls are similar to FS_IOC_FSSETXATTR ioctl()
> > > > > > > except they use *at() semantics. Therefore, there's no need to open the
> > > > > > > file to get an fd.
> > > > > > >
> > > > > > > These syscalls allow userspace to set filesystem inode attributes on
> > > > > > > special files. One of the usage examples is XFS quota projects.
> > > > > > >
> > > > > > > XFS has project quotas which could be attached to a directory. All
> > > > > > > new inodes in these directories inherit project ID set on parent
> > > > > > > directory.
> > > > > > >
> > > > > > > The project is created from userspace by opening and calling
> > > > > > > FS_IOC_FSSETXATTR on each inode. This is not possible for special
> > > > > > > files such as FIFO, SOCK, BLK etc. Therefore, some inodes are left
> > > > > > > with empty project ID. Those inodes then are not shown in the quota
> > > > > > > accounting but still exist in the directory. This is not critical but in
> > > > > > > the case when special files are created in the directory with already
> > > > > > > existing project quota, these new inodes inherit extended attributes.
> > > > > > > This creates a mix of special files with and without attributes.
> > > > > > > Moreover, special files with attributes don't have a possibility to
> > > > > > > become clear or change the attributes. This, in turn, prevents userspace
> > > > > > > from re-creating quota project on these existing files.
> > > > > > >
> > > > > > > Christian, if this get in some mergeable state, please don't merge it
> > > > > > > yet. Amir suggested these syscalls better to use updated struct fsxattr
> > > > > > > with masking from Pali Rohár patchset, so, let's see how it goes.
> > > > > >
> > > > > > Andrey,
> > > > > >
> > > > > > To be honest I don't think it would be fair to delay your syscalls more
> > > > > > than needed.
> > > > >
> > > > > I agree.
> > > > >
> > > > > > If Pali can follow through and post patches on top of your syscalls for
> > > > > > next merge window that would be great, but otherwise, I think the
> > > > > > minimum requirement is that the syscalls return EINVAL if fsx_pad
> > > > > > is not zero. we can take it from there later.
> > > > >
> > > > > IMHO SYS_getfsxattrat is fine in this form.
> > > > >
> > > > > For SYS_setfsxattrat I think there are needed some modifications
> > > > > otherwise we would have problem again with backward compatibility as
> > > > > is with ioctl if the syscall wants to be extended in future.
> > > > >
> > > > > I would suggest for following modifications for SYS_setfsxattrat:
> > > > >
> > > > > - return EINVAL if fsx_xflags contains some reserved or unsupported flag
> > > > >
> > > > > - add some flag to completely ignore fsx_extsize, fsx_projid, and
> > > > > fsx_cowextsize fields, so SYS_setfsxattrat could be used just to
> > > > > change fsx_xflags, and so could be used without the preceding
> > > > > SYS_getfsxattrat call.
> > > > >
> > > > > What do you think about it?
> > > >
> > > > I think all Andrey needs to do now is return -EINVAL if fsx_pad is not zero.
> > > >
> > > > You can use this later to extend for the semantics of flags/fields mask
> > > > and we can have a long discussion later on what this semantics should be.
> > > >
> > > > Right?
> > > >
> > > > Amir.
> > >
> > > It is really enough?
> >
> > I don't know. Let's see...
> >
> > > All new extensions later would have to be added
> > > into fsx_pad fields, and currently unused bits in fsx_xflags would be
> > > unusable for extensions.
> >
> > I am working under the assumption that the first extension would be
> > to support fsx_xflags_mask and from there, you could add filesystem
> > flags support checks and then new flags. Am I wrong?
> >
> > Obviously, fsx_xflags_mask would be taken from fsx_pad space.
> > After that extension is implemented, calling SYS_setfsxattrat() with
> > a zero fsx_xflags_mask would be silly for programs that do not do
> > the legacy get+set.
> >
> > So when we introduce fsx_xflags_mask, we could say that a value
> > of zero means that the mask is not being checked at all and unknown
> > flags in set syscall are ignored (a.k.a legacy ioctl behavior).
> >
> > Programs that actually want to try and set without get will have to set
> > a non zero fsx_xflags_mask to do something useful.
>
> Here we need to also solve the problem that without GET call we do not
> have valid values for fsx_extsize, fsx_projid, and fsx_cowextsize. So
> maybe we would need some flag in fsx_pad that fsx_extsize, fsx_projid,
> or fsx_cowextsize are ignored/masked.
>
> > I don't think this is great.
> > I would rather that the first version of syscalls will require the mask
> > and will always enforce filesystems supported flags.
>
> It is not great... But what about this? In a first step (part of this
> syscall patch series) would be just a check that fsx_pad is zero.
> Non-zero will return -EINVAL.
>
> In next changes would added fsx_filter bit field, which for each
> fsx_xflags and also for fsx_extsize, fsx_projid, and fsx_cowextsize
> fields would add a new bit flag which would say (when SET) that the
> particular thing has to be ignored.
1. I don't like the inverse mask. statx already has the stx_mask
and stx_attributes_mask, so I rather stick to same semantics
because some of those attributes are exposed via statx as well
2. fsx_*extsize already have a bit that says if that the particular
attribute is valid or not, so setting a zero fsx_cowextsize with the
flag FS_XFLAG_COWEXTSIZE has no effect in xfs:
/*
* Only set the extent size hint if we've already determined that the
* extent size hint should be set on the inode. If no extent size flags
* are set on the inode then unconditionally clear the extent size hint.
*/
if (ip->i_diflags & (XFS_DIFLAG_EXTSIZE | XFS_DIFLAG_EXTSZINHERIT))
ip->i_extsize = XFS_B_TO_FSB(mp, fa->fsx_extsize);
else
ip->i_extsize = 0;
if (xfs_has_v3inodes(mp)) {
if (ip->i_diflags2 & XFS_DIFLAG2_COWEXTSIZE)
ip->i_cowextsize = XFS_B_TO_FSB(mp, fa->fsx_cowextsize);
else
ip->i_cowextsize = 0;
}
I think we need to enforce this logic in fileattr_set_prepare()
and I think we need to add a flag FS_XFLAG_PROJID
that will be set in GET when fsx_projid != 0 and similarly
required when setting fsx_projid != 0.
Probably will need to add some backward compat glue for this
flag in GET ioctl to avoid breaking out of tree fs and fuse.
>
> So when fsx_pad is all-zeros then fsx_filter (first field in fsx_pad)
> would say that nothing in fsx_xflags, fsx_extsize, fsx_projid, and
> fsx_cowextsize is ignored, and hence behave like before.
>
> And when something in fsx_pad/fsx_filter is set then it says which
> fields are ignored/filtered-out.
>
> > If you can get those patches (on top of current series) posted and
> > reviewed in time for the next merge window, including consensus
> > on the actual semantics, that would be the best IMO.
>
> I think that this starting to be more complicated to rebase my patches
> in a way that they do not affect IOCTL path but implement it properly
> for new syscall path. It does not sounds like a trivial thing which I
> would finish in merge window time and having proper review and consensus
> on this.
>
Yes, it is better to separate the two efforts.
wrt erroring on unsupported SET flags, all fs other than xfs already
have some variant of fileattr_has_fsx(), so xfs is the only filesystem
that requires special care with the new syscalls.
It's easier to write a patch than it is to explain what I mean, so
I'll try to write a patch.
Thanks,
Amir.
^ permalink raw reply
* Re: [PATCH v4 0/3] fs: introduce getfsxattrat and setfsxattrat syscalls
From: Pali Rohár @ 2025-03-27 21:13 UTC (permalink / raw)
To: Amir Goldstein
Cc: Andrey Albershteyn, Richard Henderson, Matt Turner, Russell King,
Catalin Marinas, Will Deacon, Geert Uytterhoeven, Michal Simek,
Thomas Bogendoerfer, James E.J. Bottomley, Helge Deller,
Madhavan Srinivasan, Michael Ellerman, Nicholas Piggin,
Christophe Leroy, Naveen N Rao, Heiko Carstens, Vasily Gorbik,
Alexander Gordeev, Christian Borntraeger, Sven Schnelle,
Yoshinori Sato, Rich Felker, John Paul Adrian Glaubitz,
David S. Miller, Andreas Larsson, Andy Lutomirski,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen, x86,
H. Peter Anvin, Chris Zankel, Max Filippov, Alexander Viro,
Christian Brauner, Jan Kara, Mickaël Salaün,
Günther Noack, Arnd Bergmann, Paul Moore, James Morris,
Serge E. Hallyn, linux-alpha, linux-kernel, linux-arm-kernel,
linux-m68k, linux-mips, linux-parisc, linuxppc-dev, linux-s390,
linux-sh, sparclinux, linux-fsdevel, linux-security-module,
linux-api, linux-arch, selinux, Andrey Albershteyn, linux-xfs
In-Reply-To: <CAOQ4uxhJ53h+1AjtF4B64onqvRfZsJ3n1OFikyJpXAPTyX45iQ@mail.gmail.com>
On Thursday 27 March 2025 21:57:34 Amir Goldstein wrote:
> On Thu, Mar 27, 2025 at 8:26 PM Pali Rohár <pali@kernel.org> wrote:
> >
> > On Thursday 27 March 2025 12:47:02 Amir Goldstein wrote:
> > > On Sun, Mar 23, 2025 at 11:32 AM Pali Rohár <pali@kernel.org> wrote:
> > > >
> > > > On Sunday 23 March 2025 09:45:06 Amir Goldstein wrote:
> > > > > On Fri, Mar 21, 2025 at 8:50 PM Andrey Albershteyn <aalbersh@redhat.com> wrote:
> > > > > >
> > > > > > This patchset introduced two new syscalls getfsxattrat() and
> > > > > > setfsxattrat(). These syscalls are similar to FS_IOC_FSSETXATTR ioctl()
> > > > > > except they use *at() semantics. Therefore, there's no need to open the
> > > > > > file to get an fd.
> > > > > >
> > > > > > These syscalls allow userspace to set filesystem inode attributes on
> > > > > > special files. One of the usage examples is XFS quota projects.
> > > > > >
> > > > > > XFS has project quotas which could be attached to a directory. All
> > > > > > new inodes in these directories inherit project ID set on parent
> > > > > > directory.
> > > > > >
> > > > > > The project is created from userspace by opening and calling
> > > > > > FS_IOC_FSSETXATTR on each inode. This is not possible for special
> > > > > > files such as FIFO, SOCK, BLK etc. Therefore, some inodes are left
> > > > > > with empty project ID. Those inodes then are not shown in the quota
> > > > > > accounting but still exist in the directory. This is not critical but in
> > > > > > the case when special files are created in the directory with already
> > > > > > existing project quota, these new inodes inherit extended attributes.
> > > > > > This creates a mix of special files with and without attributes.
> > > > > > Moreover, special files with attributes don't have a possibility to
> > > > > > become clear or change the attributes. This, in turn, prevents userspace
> > > > > > from re-creating quota project on these existing files.
> > > > > >
> > > > > > Christian, if this get in some mergeable state, please don't merge it
> > > > > > yet. Amir suggested these syscalls better to use updated struct fsxattr
> > > > > > with masking from Pali Rohár patchset, so, let's see how it goes.
> > > > >
> > > > > Andrey,
> > > > >
> > > > > To be honest I don't think it would be fair to delay your syscalls more
> > > > > than needed.
> > > >
> > > > I agree.
> > > >
> > > > > If Pali can follow through and post patches on top of your syscalls for
> > > > > next merge window that would be great, but otherwise, I think the
> > > > > minimum requirement is that the syscalls return EINVAL if fsx_pad
> > > > > is not zero. we can take it from there later.
> > > >
> > > > IMHO SYS_getfsxattrat is fine in this form.
> > > >
> > > > For SYS_setfsxattrat I think there are needed some modifications
> > > > otherwise we would have problem again with backward compatibility as
> > > > is with ioctl if the syscall wants to be extended in future.
> > > >
> > > > I would suggest for following modifications for SYS_setfsxattrat:
> > > >
> > > > - return EINVAL if fsx_xflags contains some reserved or unsupported flag
> > > >
> > > > - add some flag to completely ignore fsx_extsize, fsx_projid, and
> > > > fsx_cowextsize fields, so SYS_setfsxattrat could be used just to
> > > > change fsx_xflags, and so could be used without the preceding
> > > > SYS_getfsxattrat call.
> > > >
> > > > What do you think about it?
> > >
> > > I think all Andrey needs to do now is return -EINVAL if fsx_pad is not zero.
> > >
> > > You can use this later to extend for the semantics of flags/fields mask
> > > and we can have a long discussion later on what this semantics should be.
> > >
> > > Right?
> > >
> > > Amir.
> >
> > It is really enough?
>
> I don't know. Let's see...
>
> > All new extensions later would have to be added
> > into fsx_pad fields, and currently unused bits in fsx_xflags would be
> > unusable for extensions.
>
> I am working under the assumption that the first extension would be
> to support fsx_xflags_mask and from there, you could add filesystem
> flags support checks and then new flags. Am I wrong?
>
> Obviously, fsx_xflags_mask would be taken from fsx_pad space.
> After that extension is implemented, calling SYS_setfsxattrat() with
> a zero fsx_xflags_mask would be silly for programs that do not do
> the legacy get+set.
>
> So when we introduce fsx_xflags_mask, we could say that a value
> of zero means that the mask is not being checked at all and unknown
> flags in set syscall are ignored (a.k.a legacy ioctl behavior).
>
> Programs that actually want to try and set without get will have to set
> a non zero fsx_xflags_mask to do something useful.
Here we need to also solve the problem that without GET call we do not
have valid values for fsx_extsize, fsx_projid, and fsx_cowextsize. So
maybe we would need some flag in fsx_pad that fsx_extsize, fsx_projid,
or fsx_cowextsize are ignored/masked.
> I don't think this is great.
> I would rather that the first version of syscalls will require the mask
> and will always enforce filesystems supported flags.
It is not great... But what about this? In a first step (part of this
syscall patch series) would be just a check that fsx_pad is zero.
Non-zero will return -EINVAL.
In next changes would added fsx_filter bit field, which for each
fsx_xflags and also for fsx_extsize, fsx_projid, and fsx_cowextsize
fields would add a new bit flag which would say (when SET) that the
particular thing has to be ignored.
So when fsx_pad is all-zeros then fsx_filter (first field in fsx_pad)
would say that nothing in fsx_xflags, fsx_extsize, fsx_projid, and
fsx_cowextsize is ignored, and hence behave like before.
And when something in fsx_pad/fsx_filter is set then it says which
fields are ignored/filtered-out.
> If you can get those patches (on top of current series) posted and
> reviewed in time for the next merge window, including consensus
> on the actual semantics, that would be the best IMO.
I think that this starting to be more complicated to rebase my patches
in a way that they do not affect IOCTL path but implement it properly
for new syscall path. It does not sounds like a trivial thing which I
would finish in merge window time and having proper review and consensus
on this.
> But I am just preparing a plan B in case you do not have time to
> work on the patches or if consensus on the API extensions is not
> reached on time.
>
> I think that for plan B, the minimum is to verify zero pad field and
> that is something that this syscall has to do anyway, because this
> is the way that backward compact APIs work.
>
> If you want the syscall to always return -EINVAL for setting xflags
> that are currently undefined I agree that would be nice as well.
>
> Thanks,
> Amir.
^ permalink raw reply
* Re: [PATCH v4 0/3] fs: introduce getfsxattrat and setfsxattrat syscalls
From: Amir Goldstein @ 2025-03-27 20:57 UTC (permalink / raw)
To: Pali Rohár
Cc: Andrey Albershteyn, Richard Henderson, Matt Turner, Russell King,
Catalin Marinas, Will Deacon, Geert Uytterhoeven, Michal Simek,
Thomas Bogendoerfer, James E.J. Bottomley, Helge Deller,
Madhavan Srinivasan, Michael Ellerman, Nicholas Piggin,
Christophe Leroy, Naveen N Rao, Heiko Carstens, Vasily Gorbik,
Alexander Gordeev, Christian Borntraeger, Sven Schnelle,
Yoshinori Sato, Rich Felker, John Paul Adrian Glaubitz,
David S. Miller, Andreas Larsson, Andy Lutomirski,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen, x86,
H. Peter Anvin, Chris Zankel, Max Filippov, Alexander Viro,
Christian Brauner, Jan Kara, Mickaël Salaün,
Günther Noack, Arnd Bergmann, Paul Moore, James Morris,
Serge E. Hallyn, linux-alpha, linux-kernel, linux-arm-kernel,
linux-m68k, linux-mips, linux-parisc, linuxppc-dev, linux-s390,
linux-sh, sparclinux, linux-fsdevel, linux-security-module,
linux-api, linux-arch, selinux, Andrey Albershteyn, linux-xfs
In-Reply-To: <20250327192629.ivnarhlkfbhbzjcl@pali>
On Thu, Mar 27, 2025 at 8:26 PM Pali Rohár <pali@kernel.org> wrote:
>
> On Thursday 27 March 2025 12:47:02 Amir Goldstein wrote:
> > On Sun, Mar 23, 2025 at 11:32 AM Pali Rohár <pali@kernel.org> wrote:
> > >
> > > On Sunday 23 March 2025 09:45:06 Amir Goldstein wrote:
> > > > On Fri, Mar 21, 2025 at 8:50 PM Andrey Albershteyn <aalbersh@redhat.com> wrote:
> > > > >
> > > > > This patchset introduced two new syscalls getfsxattrat() and
> > > > > setfsxattrat(). These syscalls are similar to FS_IOC_FSSETXATTR ioctl()
> > > > > except they use *at() semantics. Therefore, there's no need to open the
> > > > > file to get an fd.
> > > > >
> > > > > These syscalls allow userspace to set filesystem inode attributes on
> > > > > special files. One of the usage examples is XFS quota projects.
> > > > >
> > > > > XFS has project quotas which could be attached to a directory. All
> > > > > new inodes in these directories inherit project ID set on parent
> > > > > directory.
> > > > >
> > > > > The project is created from userspace by opening and calling
> > > > > FS_IOC_FSSETXATTR on each inode. This is not possible for special
> > > > > files such as FIFO, SOCK, BLK etc. Therefore, some inodes are left
> > > > > with empty project ID. Those inodes then are not shown in the quota
> > > > > accounting but still exist in the directory. This is not critical but in
> > > > > the case when special files are created in the directory with already
> > > > > existing project quota, these new inodes inherit extended attributes.
> > > > > This creates a mix of special files with and without attributes.
> > > > > Moreover, special files with attributes don't have a possibility to
> > > > > become clear or change the attributes. This, in turn, prevents userspace
> > > > > from re-creating quota project on these existing files.
> > > > >
> > > > > Christian, if this get in some mergeable state, please don't merge it
> > > > > yet. Amir suggested these syscalls better to use updated struct fsxattr
> > > > > with masking from Pali Rohár patchset, so, let's see how it goes.
> > > >
> > > > Andrey,
> > > >
> > > > To be honest I don't think it would be fair to delay your syscalls more
> > > > than needed.
> > >
> > > I agree.
> > >
> > > > If Pali can follow through and post patches on top of your syscalls for
> > > > next merge window that would be great, but otherwise, I think the
> > > > minimum requirement is that the syscalls return EINVAL if fsx_pad
> > > > is not zero. we can take it from there later.
> > >
> > > IMHO SYS_getfsxattrat is fine in this form.
> > >
> > > For SYS_setfsxattrat I think there are needed some modifications
> > > otherwise we would have problem again with backward compatibility as
> > > is with ioctl if the syscall wants to be extended in future.
> > >
> > > I would suggest for following modifications for SYS_setfsxattrat:
> > >
> > > - return EINVAL if fsx_xflags contains some reserved or unsupported flag
> > >
> > > - add some flag to completely ignore fsx_extsize, fsx_projid, and
> > > fsx_cowextsize fields, so SYS_setfsxattrat could be used just to
> > > change fsx_xflags, and so could be used without the preceding
> > > SYS_getfsxattrat call.
> > >
> > > What do you think about it?
> >
> > I think all Andrey needs to do now is return -EINVAL if fsx_pad is not zero.
> >
> > You can use this later to extend for the semantics of flags/fields mask
> > and we can have a long discussion later on what this semantics should be.
> >
> > Right?
> >
> > Amir.
>
> It is really enough?
I don't know. Let's see...
> All new extensions later would have to be added
> into fsx_pad fields, and currently unused bits in fsx_xflags would be
> unusable for extensions.
I am working under the assumption that the first extension would be
to support fsx_xflags_mask and from there, you could add filesystem
flags support checks and then new flags. Am I wrong?
Obviously, fsx_xflags_mask would be taken from fsx_pad space.
After that extension is implemented, calling SYS_setfsxattrat() with
a zero fsx_xflags_mask would be silly for programs that do not do
the legacy get+set.
So when we introduce fsx_xflags_mask, we could say that a value
of zero means that the mask is not being checked at all and unknown
flags in set syscall are ignored (a.k.a legacy ioctl behavior).
Programs that actually want to try and set without get will have to set
a non zero fsx_xflags_mask to do something useful.
I don't think this is great.
I would rather that the first version of syscalls will require the mask
and will always enforce filesystems supported flags.
If you can get those patches (on top of current series) posted and
reviewed in time for the next merge window, including consensus
on the actual semantics, that would be the best IMO.
But I am just preparing a plan B in case you do not have time to
work on the patches or if consensus on the API extensions is not
reached on time.
I think that for plan B, the minimum is to verify zero pad field and
that is something that this syscall has to do anyway, because this
is the way that backward compact APIs work.
If you want the syscall to always return -EINVAL for setting xflags
that are currently undefined I agree that would be nice as well.
Thanks,
Amir.
^ permalink raw reply
* Re: [PATCH v4 0/3] fs: introduce getfsxattrat and setfsxattrat syscalls
From: Pali Rohár @ 2025-03-27 19:26 UTC (permalink / raw)
To: Amir Goldstein
Cc: Andrey Albershteyn, Richard Henderson, Matt Turner, Russell King,
Catalin Marinas, Will Deacon, Geert Uytterhoeven, Michal Simek,
Thomas Bogendoerfer, James E.J. Bottomley, Helge Deller,
Madhavan Srinivasan, Michael Ellerman, Nicholas Piggin,
Christophe Leroy, Naveen N Rao, Heiko Carstens, Vasily Gorbik,
Alexander Gordeev, Christian Borntraeger, Sven Schnelle,
Yoshinori Sato, Rich Felker, John Paul Adrian Glaubitz,
David S. Miller, Andreas Larsson, Andy Lutomirski,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen, x86,
H. Peter Anvin, Chris Zankel, Max Filippov, Alexander Viro,
Christian Brauner, Jan Kara, Mickaël Salaün,
Günther Noack, Arnd Bergmann, Paul Moore, James Morris,
Serge E. Hallyn, linux-alpha, linux-kernel, linux-arm-kernel,
linux-m68k, linux-mips, linux-parisc, linuxppc-dev, linux-s390,
linux-sh, sparclinux, linux-fsdevel, linux-security-module,
linux-api, linux-arch, selinux, Andrey Albershteyn, linux-xfs
In-Reply-To: <CAOQ4uxiTKhGs1H-w1Hv-+MqY284m92Pvxfem0iWO+8THdzGvuA@mail.gmail.com>
On Thursday 27 March 2025 12:47:02 Amir Goldstein wrote:
> On Sun, Mar 23, 2025 at 11:32 AM Pali Rohár <pali@kernel.org> wrote:
> >
> > On Sunday 23 March 2025 09:45:06 Amir Goldstein wrote:
> > > On Fri, Mar 21, 2025 at 8:50 PM Andrey Albershteyn <aalbersh@redhat.com> wrote:
> > > >
> > > > This patchset introduced two new syscalls getfsxattrat() and
> > > > setfsxattrat(). These syscalls are similar to FS_IOC_FSSETXATTR ioctl()
> > > > except they use *at() semantics. Therefore, there's no need to open the
> > > > file to get an fd.
> > > >
> > > > These syscalls allow userspace to set filesystem inode attributes on
> > > > special files. One of the usage examples is XFS quota projects.
> > > >
> > > > XFS has project quotas which could be attached to a directory. All
> > > > new inodes in these directories inherit project ID set on parent
> > > > directory.
> > > >
> > > > The project is created from userspace by opening and calling
> > > > FS_IOC_FSSETXATTR on each inode. This is not possible for special
> > > > files such as FIFO, SOCK, BLK etc. Therefore, some inodes are left
> > > > with empty project ID. Those inodes then are not shown in the quota
> > > > accounting but still exist in the directory. This is not critical but in
> > > > the case when special files are created in the directory with already
> > > > existing project quota, these new inodes inherit extended attributes.
> > > > This creates a mix of special files with and without attributes.
> > > > Moreover, special files with attributes don't have a possibility to
> > > > become clear or change the attributes. This, in turn, prevents userspace
> > > > from re-creating quota project on these existing files.
> > > >
> > > > Christian, if this get in some mergeable state, please don't merge it
> > > > yet. Amir suggested these syscalls better to use updated struct fsxattr
> > > > with masking from Pali Rohár patchset, so, let's see how it goes.
> > >
> > > Andrey,
> > >
> > > To be honest I don't think it would be fair to delay your syscalls more
> > > than needed.
> >
> > I agree.
> >
> > > If Pali can follow through and post patches on top of your syscalls for
> > > next merge window that would be great, but otherwise, I think the
> > > minimum requirement is that the syscalls return EINVAL if fsx_pad
> > > is not zero. we can take it from there later.
> >
> > IMHO SYS_getfsxattrat is fine in this form.
> >
> > For SYS_setfsxattrat I think there are needed some modifications
> > otherwise we would have problem again with backward compatibility as
> > is with ioctl if the syscall wants to be extended in future.
> >
> > I would suggest for following modifications for SYS_setfsxattrat:
> >
> > - return EINVAL if fsx_xflags contains some reserved or unsupported flag
> >
> > - add some flag to completely ignore fsx_extsize, fsx_projid, and
> > fsx_cowextsize fields, so SYS_setfsxattrat could be used just to
> > change fsx_xflags, and so could be used without the preceding
> > SYS_getfsxattrat call.
> >
> > What do you think about it?
>
> I think all Andrey needs to do now is return -EINVAL if fsx_pad is not zero.
>
> You can use this later to extend for the semantics of flags/fields mask
> and we can have a long discussion later on what this semantics should be.
>
> Right?
>
> Amir.
It is really enough? All new extensions later would have to be added
into fsx_pad fields, and currently unused bits in fsx_xflags would be
unusable for extensions.
^ permalink raw reply
* Re: [PATCH v4 2/3] fs: split fileattr/fsxattr converters into helpers
From: Jan Kara @ 2025-03-27 12:32 UTC (permalink / raw)
To: Andrey Albershteyn
Cc: Richard Henderson, Matt Turner, Russell King, Catalin Marinas,
Will Deacon, Geert Uytterhoeven, Michal Simek,
Thomas Bogendoerfer, James E.J. Bottomley, Helge Deller,
Madhavan Srinivasan, Michael Ellerman, Nicholas Piggin,
Christophe Leroy, Naveen N Rao, Heiko Carstens, Vasily Gorbik,
Alexander Gordeev, Christian Borntraeger, Sven Schnelle,
Yoshinori Sato, Rich Felker, John Paul Adrian Glaubitz,
David S. Miller, Andreas Larsson, Andy Lutomirski,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen, x86,
H. Peter Anvin, Chris Zankel, Max Filippov, Alexander Viro,
Christian Brauner, Jan Kara, Mickaël Salaün,
Günther Noack, Arnd Bergmann, Pali Rohár, Paul Moore,
James Morris, Serge E. Hallyn, linux-alpha, linux-kernel,
linux-arm-kernel, linux-m68k, linux-mips, linux-parisc,
linuxppc-dev, linux-s390, linux-sh, sparclinux, linux-fsdevel,
linux-security-module, linux-api, linux-arch, Andrey Albershteyn
In-Reply-To: <20250321-xattrat-syscall-v4-2-3e82e6fb3264@kernel.org>
On Fri 21-03-25 20:48:41, Andrey Albershteyn wrote:
> This will be helpful for get/setfsxattrat syscalls to convert
> between fileattr and fsxattr.
>
> Signed-off-by: Andrey Albershteyn <aalbersh@kernel.org>
Looks good. Feel free to add:
Reviewed-by: Jan Kara <jack@suse.cz>
Honza
> ---
> fs/ioctl.c | 32 +++++++++++++++++++++-----------
> include/linux/fileattr.h | 2 ++
> 2 files changed, 23 insertions(+), 11 deletions(-)
>
> diff --git a/fs/ioctl.c b/fs/ioctl.c
> index 4434c97bc5dff5a3e8635e28745cd99404ff353e..840283d8c406623d8d26790f89b62ebcbd39e2de 100644
> --- a/fs/ioctl.c
> +++ b/fs/ioctl.c
> @@ -538,6 +538,16 @@ int vfs_fileattr_get(struct dentry *dentry, struct fileattr *fa)
> }
> EXPORT_SYMBOL(vfs_fileattr_get);
>
> +void fileattr_to_fsxattr(const struct fileattr *fa, struct fsxattr *fsx)
> +{
> + memset(fsx, 0, sizeof(struct fsxattr));
> + fsx->fsx_xflags = fa->fsx_xflags;
> + fsx->fsx_extsize = fa->fsx_extsize;
> + fsx->fsx_nextents = fa->fsx_nextents;
> + fsx->fsx_projid = fa->fsx_projid;
> + fsx->fsx_cowextsize = fa->fsx_cowextsize;
> +}
> +
> /**
> * copy_fsxattr_to_user - copy fsxattr to userspace.
> * @fa: fileattr pointer
> @@ -549,12 +559,7 @@ int copy_fsxattr_to_user(const struct fileattr *fa, struct fsxattr __user *ufa)
> {
> struct fsxattr xfa;
>
> - memset(&xfa, 0, sizeof(xfa));
> - xfa.fsx_xflags = fa->fsx_xflags;
> - xfa.fsx_extsize = fa->fsx_extsize;
> - xfa.fsx_nextents = fa->fsx_nextents;
> - xfa.fsx_projid = fa->fsx_projid;
> - xfa.fsx_cowextsize = fa->fsx_cowextsize;
> + fileattr_to_fsxattr(fa, &xfa);
>
> if (copy_to_user(ufa, &xfa, sizeof(xfa)))
> return -EFAULT;
> @@ -563,6 +568,15 @@ int copy_fsxattr_to_user(const struct fileattr *fa, struct fsxattr __user *ufa)
> }
> EXPORT_SYMBOL(copy_fsxattr_to_user);
>
> +void fsxattr_to_fileattr(const struct fsxattr *fsx, struct fileattr *fa)
> +{
> + fileattr_fill_xflags(fa, fsx->fsx_xflags);
> + fa->fsx_extsize = fsx->fsx_extsize;
> + fa->fsx_nextents = fsx->fsx_nextents;
> + fa->fsx_projid = fsx->fsx_projid;
> + fa->fsx_cowextsize = fsx->fsx_cowextsize;
> +}
> +
> static int copy_fsxattr_from_user(struct fileattr *fa,
> struct fsxattr __user *ufa)
> {
> @@ -571,11 +585,7 @@ static int copy_fsxattr_from_user(struct fileattr *fa,
> if (copy_from_user(&xfa, ufa, sizeof(xfa)))
> return -EFAULT;
>
> - fileattr_fill_xflags(fa, xfa.fsx_xflags);
> - fa->fsx_extsize = xfa.fsx_extsize;
> - fa->fsx_nextents = xfa.fsx_nextents;
> - fa->fsx_projid = xfa.fsx_projid;
> - fa->fsx_cowextsize = xfa.fsx_cowextsize;
> + fsxattr_to_fileattr(&xfa, fa);
>
> return 0;
> }
> diff --git a/include/linux/fileattr.h b/include/linux/fileattr.h
> index 47c05a9851d0600964b644c9c7218faacfd865f8..31888fa2edf10050be134f587299256088344365 100644
> --- a/include/linux/fileattr.h
> +++ b/include/linux/fileattr.h
> @@ -33,7 +33,9 @@ struct fileattr {
> bool fsx_valid:1;
> };
>
> +void fileattr_to_fsxattr(const struct fileattr *fa, struct fsxattr *fsx);
> int copy_fsxattr_to_user(const struct fileattr *fa, struct fsxattr __user *ufa);
> +void fsxattr_to_fileattr(const struct fsxattr *fsx, struct fileattr *fa);
>
> void fileattr_fill_xflags(struct fileattr *fa, u32 xflags);
> void fileattr_fill_flags(struct fileattr *fa, u32 flags);
>
> --
> 2.47.2
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
^ permalink raw reply
* Re: [PATCH v4 3/3] fs: introduce getfsxattrat and setfsxattrat syscalls
From: Jan Kara @ 2025-03-27 12:31 UTC (permalink / raw)
To: Andrey Albershteyn
Cc: Richard Henderson, Matt Turner, Russell King, Catalin Marinas,
Will Deacon, Geert Uytterhoeven, Michal Simek,
Thomas Bogendoerfer, James E.J. Bottomley, Helge Deller,
Madhavan Srinivasan, Michael Ellerman, Nicholas Piggin,
Christophe Leroy, Naveen N Rao, Heiko Carstens, Vasily Gorbik,
Alexander Gordeev, Christian Borntraeger, Sven Schnelle,
Yoshinori Sato, Rich Felker, John Paul Adrian Glaubitz,
David S. Miller, Andreas Larsson, Andy Lutomirski,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen, x86,
H. Peter Anvin, Chris Zankel, Max Filippov, Alexander Viro,
Christian Brauner, Jan Kara, Mickaël Salaün,
Günther Noack, Arnd Bergmann, Pali Rohár, Paul Moore,
James Morris, Serge E. Hallyn, linux-alpha, linux-kernel,
linux-arm-kernel, linux-m68k, linux-mips, linux-parisc,
linuxppc-dev, linux-s390, linux-sh, sparclinux, linux-fsdevel,
linux-security-module, linux-api, linux-arch, linux-xfs
In-Reply-To: <20250321-xattrat-syscall-v4-3-3e82e6fb3264@kernel.org>
On Fri 21-03-25 20:48:42, Andrey Albershteyn wrote:
> From: Andrey Albershteyn <aalbersh@redhat.com>
>
> Introduce getfsxattrat and setfsxattrat syscalls to manipulate inode
> extended attributes/flags. The syscalls take parent directory fd and
> path to the child together with struct fsxattr.
>
> This is an alternative to FS_IOC_FSSETXATTR ioctl with a difference
> that file don't need to be open as we can reference it with a path
> instead of fd. By having this we can manipulated inode extended
> attributes not only on regular files but also on special ones. This
> is not possible with FS_IOC_FSSETXATTR ioctl as with special files
> we can not call ioctl() directly on the filesystem inode using fd.
>
> This patch adds two new syscalls which allows userspace to get/set
> extended inode attributes on special files by using parent directory
> and a path - *at() like syscall.
>
> CC: linux-api@vger.kernel.org
> CC: linux-fsdevel@vger.kernel.org
> CC: linux-xfs@vger.kernel.org
> Signed-off-by: Andrey Albershteyn <aalbersh@redhat.com>
> Acked-by: Arnd Bergmann <arnd@arndb.de>
Looks good. Just two nits below:
> +SYSCALL_DEFINE5(getfsxattrat, int, dfd, const char __user *, filename,
> + struct fsxattr __user *, ufsx, size_t, usize,
> + unsigned int, at_flags)
> +{
> + struct fileattr fa = {};
> + struct path filepath;
> + int error;
> + unsigned int lookup_flags = 0;
> + struct filename *name;
> + struct fsxattr fsx = {};
> +
> + BUILD_BUG_ON(sizeof(struct fsxattr) < FSXATTR_SIZE_VER0);
> + BUILD_BUG_ON(sizeof(struct fsxattr) != FSXATTR_SIZE_LATEST);
> +
> + if ((at_flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
> + return -EINVAL;
> +
> + if (!(at_flags & AT_SYMLINK_NOFOLLOW))
> + lookup_flags |= LOOKUP_FOLLOW;
> +
> + if (at_flags & AT_EMPTY_PATH)
> + lookup_flags |= LOOKUP_EMPTY;
Strictly speaking setting LOOKUP_EMPTY does not have any effect because
empty names are already handled by getname_maybe_null(). But it does not
hurt either so I don't really care...
> +
> + if (usize > PAGE_SIZE)
> + return -E2BIG;
> +
> + if (usize < FSXATTR_SIZE_VER0)
> + return -EINVAL;
> +
> + name = getname_maybe_null(filename, at_flags);
> + if (!name) {
> + CLASS(fd, f)(dfd);
> +
> + if (fd_empty(f))
> + return -EBADF;
> + error = vfs_fileattr_get(file_dentry(fd_file(f)), &fa);
> + } else {
> + error = filename_lookup(dfd, name, lookup_flags, &filepath,
> + NULL);
> + if (error)
> + goto out;
> + error = vfs_fileattr_get(filepath.dentry, &fa);
> + path_put(&filepath);
> + }
> + if (error == -ENOIOCTLCMD)
> + error = -EOPNOTSUPP;
> + if (!error) {
> + fileattr_to_fsxattr(&fa, &fsx);
> + error = copy_struct_to_user(ufsx, usize, &fsx,
> + sizeof(struct fsxattr), NULL);
> + }
> +out:
> + putname(name);
> + return error;
> +}
> +
> +SYSCALL_DEFINE5(setfsxattrat, int, dfd, const char __user *, filename,
> + struct fsxattr __user *, ufsx, size_t, usize,
> + unsigned int, at_flags)
> +{
> + struct fileattr fa;
> + struct path filepath;
> + int error;
> + unsigned int lookup_flags = 0;
> + struct filename *name;
> + struct mnt_idmap *idmap;
> + struct dentry *dentry;
> + struct vfsmount *mnt;
> + struct fsxattr fsx = {};
> +
> + BUILD_BUG_ON(sizeof(struct fsxattr) < FSXATTR_SIZE_VER0);
> + BUILD_BUG_ON(sizeof(struct fsxattr) != FSXATTR_SIZE_LATEST);
> +
> + if ((at_flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
> + return -EINVAL;
> +
> + if (!(at_flags & AT_SYMLINK_NOFOLLOW))
> + lookup_flags |= LOOKUP_FOLLOW;
> +
> + if (at_flags & AT_EMPTY_PATH)
> + lookup_flags |= LOOKUP_EMPTY;
Same comment regarding LOOKUP_EMPTY here.
> +
> + if (usize > PAGE_SIZE)
> + return -E2BIG;
> +
> + if (usize < FSXATTR_SIZE_VER0)
> + return -EINVAL;
> +
> + error = copy_struct_from_user(&fsx, sizeof(struct fsxattr), ufsx, usize);
> + if (error)
> + return error;
> +
> + fsxattr_to_fileattr(&fsx, &fa);
> +
> + name = getname_maybe_null(filename, at_flags);
> + if (!name) {
> + CLASS(fd, f)(dfd);
> +
> + if (fd_empty(f))
> + return -EBADF;
> +
> + idmap = file_mnt_idmap(fd_file(f));
> + dentry = file_dentry(fd_file(f));
> + mnt = fd_file(f)->f_path.mnt;
> + } else {
> + error = filename_lookup(dfd, name, lookup_flags, &filepath,
> + NULL);
> + if (error)
> + return error;
> +
> + idmap = mnt_idmap(filepath.mnt);
> + dentry = filepath.dentry;
> + mnt = filepath.mnt;
> + }
> +
> + error = mnt_want_write(mnt);
> + if (!error) {
> + error = vfs_fileattr_set(idmap, dentry, &fa);
> + if (error == -ENOIOCTLCMD)
> + error = -EOPNOTSUPP;
> + mnt_drop_write(mnt);
> + }
> +
> + path_put(&filepath);
filepath will not be initialized here in case of name == NULL.
> + return error;
> +}
With this fixed feel free to add:
Reviewed-by: Jan Kara <jack@suse.cz>
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
^ permalink raw reply
* Re: [PATCH v4 0/3] fs: introduce getfsxattrat and setfsxattrat syscalls
From: Amir Goldstein @ 2025-03-27 11:47 UTC (permalink / raw)
To: Pali Rohár
Cc: Andrey Albershteyn, Richard Henderson, Matt Turner, Russell King,
Catalin Marinas, Will Deacon, Geert Uytterhoeven, Michal Simek,
Thomas Bogendoerfer, James E.J. Bottomley, Helge Deller,
Madhavan Srinivasan, Michael Ellerman, Nicholas Piggin,
Christophe Leroy, Naveen N Rao, Heiko Carstens, Vasily Gorbik,
Alexander Gordeev, Christian Borntraeger, Sven Schnelle,
Yoshinori Sato, Rich Felker, John Paul Adrian Glaubitz,
David S. Miller, Andreas Larsson, Andy Lutomirski,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen, x86,
H. Peter Anvin, Chris Zankel, Max Filippov, Alexander Viro,
Christian Brauner, Jan Kara, Mickaël Salaün,
Günther Noack, Arnd Bergmann, Paul Moore, James Morris,
Serge E. Hallyn, linux-alpha, linux-kernel, linux-arm-kernel,
linux-m68k, linux-mips, linux-parisc, linuxppc-dev, linux-s390,
linux-sh, sparclinux, linux-fsdevel, linux-security-module,
linux-api, linux-arch, selinux, Andrey Albershteyn, linux-xfs
In-Reply-To: <20250323103234.2mwhpsbigpwtiby4@pali>
On Sun, Mar 23, 2025 at 11:32 AM Pali Rohár <pali@kernel.org> wrote:
>
> On Sunday 23 March 2025 09:45:06 Amir Goldstein wrote:
> > On Fri, Mar 21, 2025 at 8:50 PM Andrey Albershteyn <aalbersh@redhat.com> wrote:
> > >
> > > This patchset introduced two new syscalls getfsxattrat() and
> > > setfsxattrat(). These syscalls are similar to FS_IOC_FSSETXATTR ioctl()
> > > except they use *at() semantics. Therefore, there's no need to open the
> > > file to get an fd.
> > >
> > > These syscalls allow userspace to set filesystem inode attributes on
> > > special files. One of the usage examples is XFS quota projects.
> > >
> > > XFS has project quotas which could be attached to a directory. All
> > > new inodes in these directories inherit project ID set on parent
> > > directory.
> > >
> > > The project is created from userspace by opening and calling
> > > FS_IOC_FSSETXATTR on each inode. This is not possible for special
> > > files such as FIFO, SOCK, BLK etc. Therefore, some inodes are left
> > > with empty project ID. Those inodes then are not shown in the quota
> > > accounting but still exist in the directory. This is not critical but in
> > > the case when special files are created in the directory with already
> > > existing project quota, these new inodes inherit extended attributes.
> > > This creates a mix of special files with and without attributes.
> > > Moreover, special files with attributes don't have a possibility to
> > > become clear or change the attributes. This, in turn, prevents userspace
> > > from re-creating quota project on these existing files.
> > >
> > > Christian, if this get in some mergeable state, please don't merge it
> > > yet. Amir suggested these syscalls better to use updated struct fsxattr
> > > with masking from Pali Rohár patchset, so, let's see how it goes.
> >
> > Andrey,
> >
> > To be honest I don't think it would be fair to delay your syscalls more
> > than needed.
>
> I agree.
>
> > If Pali can follow through and post patches on top of your syscalls for
> > next merge window that would be great, but otherwise, I think the
> > minimum requirement is that the syscalls return EINVAL if fsx_pad
> > is not zero. we can take it from there later.
>
> IMHO SYS_getfsxattrat is fine in this form.
>
> For SYS_setfsxattrat I think there are needed some modifications
> otherwise we would have problem again with backward compatibility as
> is with ioctl if the syscall wants to be extended in future.
>
> I would suggest for following modifications for SYS_setfsxattrat:
>
> - return EINVAL if fsx_xflags contains some reserved or unsupported flag
>
> - add some flag to completely ignore fsx_extsize, fsx_projid, and
> fsx_cowextsize fields, so SYS_setfsxattrat could be used just to
> change fsx_xflags, and so could be used without the preceding
> SYS_getfsxattrat call.
>
> What do you think about it?
I think all Andrey needs to do now is return -EINVAL if fsx_pad is not zero.
You can use this later to extend for the semantics of flags/fields mask
and we can have a long discussion later on what this semantics should be.
Right?
Amir.
^ permalink raw reply
* error handling recvfrom(2)
From: Peter Radisson @ 2025-03-27 11:45 UTC (permalink / raw)
To: linux-api
Hi list,
I noted the error handling in recvfrom(2) is wired.
note i will only talk about src_addr and addrlen in the case
src_addr != NULL. I have tested with kernel 5.14.
Function: the kernel shall fill the user supplied structure in src_addr
what should be addrlen in size (should be sizeof struct sockaddr ).
regarding addrlen i found the follwing behavier:
addrlen < 0 errno=EINVAL
0<= addrlen < sizeof struct sockaddr no errno set
IMHO recvfrom(2) should report an error here also.
while testing i noted that the case addrlen < 0 is checked
after the call. What means if you use a blocking recvfrom,
the call waits for an answer only to report an error afterwards.
IMHO the check for space should be done before.
What is the rationale behind this ?
If not can that be changed ?
note: please reply directly i am not a list member
note: I send also a mail to the man-page list to improve the
documentation of the current state
CU
^ permalink raw reply
* Re: [PATCH v4 3/3] fs: introduce getfsxattrat and setfsxattrat syscalls
From: Amir Goldstein @ 2025-03-27 11:39 UTC (permalink / raw)
To: Andrey Albershteyn
Cc: Richard Henderson, Matt Turner, Russell King, Catalin Marinas,
Will Deacon, Geert Uytterhoeven, Michal Simek,
Thomas Bogendoerfer, James E.J. Bottomley, Helge Deller,
Madhavan Srinivasan, Michael Ellerman, Nicholas Piggin,
Christophe Leroy, Naveen N Rao, Heiko Carstens, Vasily Gorbik,
Alexander Gordeev, Christian Borntraeger, Sven Schnelle,
Yoshinori Sato, Rich Felker, John Paul Adrian Glaubitz,
David S. Miller, Andreas Larsson, Andy Lutomirski,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen, x86,
H. Peter Anvin, Chris Zankel, Max Filippov, Alexander Viro,
Christian Brauner, Jan Kara, Mickaël Salaün,
Günther Noack, Arnd Bergmann, Pali Rohár, Paul Moore,
James Morris, Serge E. Hallyn, linux-alpha, linux-kernel,
linux-arm-kernel, linux-m68k, linux-mips, linux-parisc,
linuxppc-dev, linux-s390, linux-sh, sparclinux, linux-fsdevel,
linux-security-module, linux-api, linux-arch, linux-xfs
In-Reply-To: <faqun3wrpvwrhwukql3niqvvauy5ngrpytx5bxbrv5xkounez3@m7j2znjuzapu>
On Thu, Mar 27, 2025 at 10:33 AM Andrey Albershteyn <aalbersh@redhat.com> wrote:
>
> On 2025-03-23 09:56:25, Amir Goldstein wrote:
> > On Fri, Mar 21, 2025 at 8:49 PM Andrey Albershteyn <aalbersh@redhat.com> wrote:
> > >
> > > From: Andrey Albershteyn <aalbersh@redhat.com>
> > >
> > > Introduce getfsxattrat and setfsxattrat syscalls to manipulate inode
> > > extended attributes/flags. The syscalls take parent directory fd and
> > > path to the child together with struct fsxattr.
> > >
> > > This is an alternative to FS_IOC_FSSETXATTR ioctl with a difference
> > > that file don't need to be open as we can reference it with a path
> > > instead of fd. By having this we can manipulated inode extended
> > > attributes not only on regular files but also on special ones. This
> > > is not possible with FS_IOC_FSSETXATTR ioctl as with special files
> > > we can not call ioctl() directly on the filesystem inode using fd.
> > >
> > > This patch adds two new syscalls which allows userspace to get/set
> > > extended inode attributes on special files by using parent directory
> > > and a path - *at() like syscall.
> > >
> > > CC: linux-api@vger.kernel.org
> > > CC: linux-fsdevel@vger.kernel.org
> > > CC: linux-xfs@vger.kernel.org
> > > Signed-off-by: Andrey Albershteyn <aalbersh@redhat.com>
> > > Acked-by: Arnd Bergmann <arnd@arndb.de>
> > > ---
> > ...
> > > +SYSCALL_DEFINE5(setfsxattrat, int, dfd, const char __user *, filename,
> > > + struct fsxattr __user *, ufsx, size_t, usize,
> > > + unsigned int, at_flags)
> > > +{
> > > + struct fileattr fa;
> > > + struct path filepath;
> > > + int error;
> > > + unsigned int lookup_flags = 0;
> > > + struct filename *name;
> > > + struct mnt_idmap *idmap;.
> >
> > > + struct dentry *dentry;
> > > + struct vfsmount *mnt;
> > > + struct fsxattr fsx = {};
> > > +
> > > + BUILD_BUG_ON(sizeof(struct fsxattr) < FSXATTR_SIZE_VER0);
> > > + BUILD_BUG_ON(sizeof(struct fsxattr) != FSXATTR_SIZE_LATEST);
> > > +
> > > + if ((at_flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
> > > + return -EINVAL;
> > > +
> > > + if (!(at_flags & AT_SYMLINK_NOFOLLOW))
> > > + lookup_flags |= LOOKUP_FOLLOW;
> > > +
> > > + if (at_flags & AT_EMPTY_PATH)
> > > + lookup_flags |= LOOKUP_EMPTY;
> > > +
> > > + if (usize > PAGE_SIZE)
> > > + return -E2BIG;
> > > +
> > > + if (usize < FSXATTR_SIZE_VER0)
> > > + return -EINVAL;
> > > +
> > > + error = copy_struct_from_user(&fsx, sizeof(struct fsxattr), ufsx, usize);
> > > + if (error)
> > > + return error;
> > > +
> > > + fsxattr_to_fileattr(&fsx, &fa);
> > > +
> > > + name = getname_maybe_null(filename, at_flags);
> > > + if (!name) {
> > > + CLASS(fd, f)(dfd);
> > > +
> > > + if (fd_empty(f))
> > > + return -EBADF;
> > > +
> > > + idmap = file_mnt_idmap(fd_file(f));
> > > + dentry = file_dentry(fd_file(f));
> > > + mnt = fd_file(f)->f_path.mnt;
> > > + } else {
> > > + error = filename_lookup(dfd, name, lookup_flags, &filepath,
> > > + NULL);
> > > + if (error)
> > > + return error;
> > > +
> > > + idmap = mnt_idmap(filepath.mnt);
> > > + dentry = filepath.dentry;
> > > + mnt = filepath.mnt;
> > > + }
> > > +
> > > + error = mnt_want_write(mnt);
> > > + if (!error) {
> > > + error = vfs_fileattr_set(idmap, dentry, &fa);
> > > + if (error == -ENOIOCTLCMD)
> > > + error = -EOPNOTSUPP;
> >
> > This is awkward.
> > vfs_fileattr_set() should return -EOPNOTSUPP.
> > ioctl_setflags() could maybe convert it to -ENOIOCTLCMD,
> > but looking at similar cases ioctl_fiemap(), ioctl_fsfreeze() the
> > ioctl returns -EOPNOTSUPP.
> >
> > I don't think it is necessarily a bad idea to start returning
> > -EOPNOTSUPP instead of -ENOIOCTLCMD for the ioctl
> > because that really reflects the fact that the ioctl is now implemented
> > in vfs and not in the specific fs.
> >
> > and I think it would not be a bad idea at all to make that change
> > together with the merge of the syscalls as a sort of hint to userspace
> > that uses the ioctl, that the sycalls API exists.
> >
> > Thanks,
> > Amir.
> >
>
> Hmm, not sure what you're suggesting here. I see it as:
> - get/setfsxattrat should return EOPNOTSUPP as it make more sense
> than ENOIOCTLCMD
> - ioctl_setflags returns ENOIOCTLCMD which also expected
>
> Don't really see a reason to change what vfs_fileattr_set() returns
> and then copying this if() to other places or start returning
> EOPNOTSUPP.
ENOIOCTLCMD conceptually means that the ioctl command is unknown
This is not the case since ->fileattr_[gs]et() became a vfs API
the ioctl command is handled by vfs and it is known, but individual
filesystems may not support it, so conceptually, returning EOPNOTSUPP
from ioctl() is more correct these days, exactly as is done with the ioctls
FS_IOC_FIEMAP and FIFREEZE which were also historically per fs
ioctls and made into a vfs API.
The fact that bcachefs does not implement ->fileattr_[gs]et() and does
implement FS_IOC_FS[GS]ETXATTR is an oversight IMO, since it
was probably merged after the vfs conversion patch.
This mistake means that bcachefs fileattr cannot be copied up by
ovl_copy_fileattr() which uses the vfs API and NOT the ioctl.
However, if you would made the internal vfs API change that I suggested,
it will have broken ovl_real_fileattr_get() and ovl_copy_fileattr(),
so leave it for now - if I care enough I can do it later together with
fixing the overlayfs and fuse code.
Thanks,
Amir.
^ permalink raw reply
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