Re: [RFC PATCH v2 2/4] tsm: Add RTMRs to the configfs-tsm hierarchy

Mikko Ylinen
2024-02-21T16:17:02Z

Hi,

On Sun, Jan 28, 2024 at 10:25:21PM +0100, Samuel Ortiz wrote:
> RTMRs are defined and managed by their corresponding TSM provider. As
> such, they can be configured through the TSM configfs root.
>
> An additional `rtmrs` directory is added by default under the `tsm` one,
> where each supported RTMR can be configured:
>
> mkdir /sys/kernel/config/tsm/rtmrs/rtmr0
> echo 0 > /sys/kernel/config/tsm/rtmrs/rtmr0/index

I implemented the plumbing for TDX to experiment with this patchset a bit
and to try out some ideas for the event logging.

The first mkdir triggers the following, FYI:

[ 353.984801] ======================================================
[ 353.984805] WARNING: possible circular locking dependency detected
[ 353.984808] 6.8.0-rc5+ #14 Not tainted
[ 353.984812] ------------------------------------------------------
[ 353.984814] mkdir/3374 is trying to acquire lock:
[ 353.984817] ffffffff8ae59d90 (tsm_rwsem){++++}-{3:3}, at: tsm_rtmrs_make_item+0x26/0xa0
[ 353.984830]
but task is already holding lock:
[ 353.984832] ffffffff8ae59890 (tsm_configfs.su_mutex){+.+.}-{3:3}, at: configfs_mkdir+0x188/0x470
[ 353.984842]
which lock already depends on the new lock.

[ 353.984845]
the existing dependency chain (in reverse order) is:
[ 353.984848]
-> #1 (tsm_configfs.su_mutex){+.+.}-{3:3}:
[ 353.984853] __lock_acquire+0x4d1/0xbb0
[ 353.984861] lock_acquire+0xcb/0x2b0
[ 353.984863] __mutex_lock+0x9b/0xb80
[ 353.984874] mutex_lock_nested+0x1f/0x30
[ 353.984878] configfs_register_group+0x7b/0x1d0
[ 353.984880] configfs_register_default_group+0x54/0x90
[ 353.984883] tsm_rtmr_register+0xb9/0x140
[ 353.984886] tsm_register+0x89/0xc0
[ 353.984888] tdx_guest_init+0x81/0x110
[ 353.984896] do_one_initcall+0x62/0x370
[ 353.984903] do_initcalls+0xe3/0x1a0
[ 353.984909] kernel_init_freeable+0x2ea/0x400
[ 353.984912] kernel_init+0x1e/0x1c0
[ 353.984915] ret_from_fork+0x3e/0x60
[ 353.984921] ret_from_fork_asm+0x11/0x20
[ 353.984925]
-> #0 (tsm_rwsem){++++}-{3:3}:
[ 353.984929] check_prev_add+0xed/0xc60
[ 353.984931] validate_chain+0x488/0x530
[ 353.984933] __lock_acquire+0x4d1/0xbb0
[ 353.984936] lock_acquire+0xcb/0x2b0
[ 353.984938] down_read+0x45/0x190
[ 353.984941] tsm_rtmrs_make_item+0x26/0xa0
[ 353.984944] configfs_mkdir+0x349/0x470
[ 353.984946] vfs_mkdir+0x1a5/0x260
[ 353.984955] do_mkdirat+0x83/0x140
[ 353.984958] __x64_sys_mkdir+0x4e/0x70
[ 353.984960] do_syscall_64+0x67/0x110
[ 353.984964] entry_SYSCALL_64_after_hwframe+0x63/0x6b
[ 353.984972]
other info that might help us debug this:

[ 353.984975] Possible unsafe locking scenario:

[ 353.984977] CPU0 CPU1
[ 353.984980] ---- ----
[ 353.984982] lock(tsm_configfs.su_mutex);
[ 353.984985] lock(tsm_rwsem);
[ 353.984988] lock(tsm_configfs.su_mutex);
[ 353.984991] rlock(tsm_rwsem);
[ 353.984993]
*** DEADLOCK ***

[ 353.984996] 3 locks held by mkdir/3374:
[ 353.984998] #0: ff3af65b4ae05408 (sb_writers#13){.+.+}-{0:0}, at: filename_create+0x61/0x190
[ 353.985006] #1: ff3af65b492a97f8 (&sb->s_type->i_mutex_key#6/1){+.+.}-{3:3}, at: filename_create+0x9d/
0x190
[ 353.985014] #2: ffffffff8ae59890 (tsm_configfs.su_mutex){+.+.}-{3:3}, at: configfs_mkdir+0x188/0x470
[ 353.985020]
stack backtrace:
[ 353.985023] CPU: 36 PID: 3374 Comm: mkdir Not tainted 6.8.0-rc5+ #14
[ 353.985027] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 2023.05-2+tdx1.0 11/05/2023
[ 353.985031] Call Trace:
[ 353.985033] <TASK>
[ 353.985034] dump_stack_lvl+0x4e/0x90
[ 353.985041] dump_stack+0x14/0x20
[ 353.985044] print_circular_bug+0xec/0x110
[ 353.985047] check_noncircular+0x130/0x150
[ 353.985051] check_prev_add+0xed/0xc60
[ 353.985053] ? add_chain_cache+0x10e/0x2d0
[ 353.985059] validate_chain+0x488/0x530
[ 353.985062] __lock_acquire+0x4d1/0xbb0
[ 353.985065] lock_acquire+0xcb/0x2b0
[ 353.985067] ? tsm_rtmrs_make_item+0x26/0xa0
[ 353.985071] down_read+0x45/0x190
[ 353.985074] ? tsm_rtmrs_make_item+0x26/0xa0
[ 353.985094] tsm_rtmrs_make_item+0x26/0xa0
[ 353.985097] configfs_mkdir+0x349/0x470
[ 353.985100] vfs_mkdir+0x1a5/0x260
[ 353.985105] do_mkdirat+0x83/0x140
[ 353.985109] __x64_sys_mkdir+0x4e/0x70
[ 353.985112] do_syscall_64+0x67/0x110
[ 353.985116] entry_SYSCALL_64_after_hwframe+0x63/0x6b
[ 353.985119] RIP: 0033:0x7f35aad19d4b
[ 353.985124] Code: 0f 1e fa 48 89 f2 b9 00 01 00 00 48 89 fe bf 9c ff ff ff e9 d7 c6 ff ff 0f 1f 80 00 0
0 00 00 f3 0f 1e fa b8 53 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 05 c3 0f 1f 40 00 48 8b 15 99 40 0e 00 f7
d8
[ 353.985132] RSP: 002b:00007ffc3f2ccc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000053
[ 353.985139] RAX: ffffffffffffffda RBX: 00007ffc3f2cd5a5 RCX: 00007f35aad19d4b
[ 353.985143] RDX: 0000000000000000 RSI: 00000000000001ff RDI: 00007ffc3f2cd5a5
[ 353.985147] RBP: 00000000000001ff R08: 00000000000001ff R09: 0000000000000000
[ 353.985151] R10: 0000556f33617249 R11: 0000000000000246 R12: 0000000000000000
[ 353.985155] R13: 00007ffc3f2cce18 R14: 0000000000000000 R15: 00007ffc3f2cd5a5
[ 353.985161] </TASK>

>
> An RTMR can not be extended nor read before its configured by assigning
> it an index. It is the TSM backend responsibility and choice to map that
> index to a hardware RTMR.
>
> Signed-off-by: Samuel Ortiz <sameo@rivosinc.com>
> ---
> Documentation/ABI/testing/configfs-tsm | 11 ++
> drivers/virt/coco/tsm.c | 164 +++++++++++++++++++++++++
> 2 files changed, 175 insertions(+)
>
> diff --git a/Documentation/ABI/testing/configfs-tsm b/Documentation/ABI/testing/configfs-tsm
> index dd24202b5ba5..590e103a9bcd 100644
> --- a/Documentation/ABI/testing/configfs-tsm
> +++ b/Documentation/ABI/testing/configfs-tsm
> @@ -80,3 +80,14 @@ Contact: linux-coco@lists.linux.dev
> Description:
> (RO) Indicates the minimum permissible value that can be written
> to @privlevel.
> +
> +What: /sys/kernel/config/tsm/rtmrs/$name/index
> +Date: January, 2024
> +KernelVersion: v6.8
> +Contact: linux-coco@lists.linux.dev
> +Description:
> + (RW) A Runtime Measurement Register (RTMR) hardware index.
> + Once created under /sys/kernel/config/tsm/rtmrs/, an RTMR entry
> + can be mapped to a hardware RTMR by writing into its index
> + attribute. The TSM provider will then map the configfs entry to
> + its corresponding hardware register.
> diff --git a/drivers/virt/coco/tsm.c b/drivers/virt/coco/tsm.c
> index 1a8c3c096120..bb9ed2d2accc 100644
> --- a/drivers/virt/coco/tsm.c
> +++ b/drivers/virt/coco/tsm.c
> @@ -419,6 +419,108 @@ static const struct config_item_type tsm_reports_type = {
> .ct_group_ops = &tsm_report_group_ops,
> };
>
> +static ssize_t tsm_rtmr_index_store(struct config_item *cfg,
> + const char *buf, size_t len)
> +{
> + struct tsm_rtmr_state *rtmr_state = to_tsm_rtmr_state(cfg);
> + const struct tsm_ops *ops;
> + unsigned int val;
> + int rc;
> +
> + rc = kstrtouint(buf, 0, &val);
> + if (rc)
> + return rc;
> +
> + guard(rwsem_write)(&tsm_rwsem);
> +
> + /* Index can only be configured once */
> + if (is_rtmr_configured(rtmr_state))
> + return -EBUSY;
> +
> + /* Check that index stays within the TSM provided capabilities */
> + ops = provider.ops;
> + if (!ops)
> + return -ENOTTY;
> +
> + if (val > ops->capabilities.num_rtmrs - 1)
> + return -EINVAL;
> +
> + /* Check that this index is available */
> + if (tsm_rtmrs->rtmrs[val])
> + return -EINVAL;
> +
> + rtmr_state->index = val;
> + rtmr_state->alg = ops->capabilities.rtmrs[val].hash_alg;
> +
> + tsm_rtmrs->rtmrs[val] = rtmr_state;
> +
> + return len;
> +}
> +
> +static ssize_t tsm_rtmr_index_show(struct config_item *cfg,
> + char *buf)
> +{
> + struct tsm_rtmr_state *rtmr_state = to_tsm_rtmr_state(cfg);
> +
> + guard(rwsem_read)(&tsm_rwsem);
> +
> + /* An RTMR is not available if it has not been configured */
> + if (!is_rtmr_configured(rtmr_state))
> + return -ENXIO;
> +
> + return sysfs_emit(buf, "%u\n", rtmr_state->index);
> +}
> +CONFIGFS_ATTR(tsm_rtmr_, index);
> +
> +static struct configfs_attribute *tsm_rtmr_attrs[] = {
> + &tsm_rtmr_attr_index,
> + NULL,
> +};
> +
> +static void tsm_rtmr_item_release(struct config_item *cfg)
> +{
> + struct tsm_rtmr_state *state = to_tsm_rtmr_state(cfg);
> +
> + kfree(state);
> +}
> +
> +static struct configfs_item_operations tsm_rtmr_item_ops = {
> + .release = tsm_rtmr_item_release,
> +};
> +
> +const struct config_item_type tsm_rtmr_type = {
> + .ct_owner = THIS_MODULE,
> + .ct_attrs = tsm_rtmr_attrs,
> + .ct_item_ops = &tsm_rtmr_item_ops,
> +};
> +
> +static struct config_item *tsm_rtmrs_make_item(struct config_group *group,
> + const char *name)
> +{
> + struct tsm_rtmr_state *state;
> +
> + guard(rwsem_read)(&tsm_rwsem);
> + if (!(provider.ops && (provider.ops->capabilities.num_rtmrs > 0)))
> + return ERR_PTR(-ENXIO);
> +
> + state = kzalloc(sizeof(*state), GFP_KERNEL);
> + if (!state)
> + return ERR_PTR(-ENOMEM);
> + state->index = U32_MAX;
> +
> + config_item_init_type_name(&state->cfg, name, &tsm_rtmr_type);
> + return &state->cfg;
> +}
> +
> +static struct configfs_group_operations tsm_rtmrs_group_ops = {
> + .make_item = tsm_rtmrs_make_item,
> +};
> +
> +static const struct config_item_type tsm_rtmrs_type = {
> + .ct_owner = THIS_MODULE,
> + .ct_group_ops = &tsm_rtmrs_group_ops,
> +};
> +
> static const struct config_item_type tsm_root_group_type = {
> .ct_owner = THIS_MODULE,
> };
> @@ -433,10 +535,48 @@ static struct configfs_subsystem tsm_configfs = {
> .su_mutex = __MUTEX_INITIALIZER(tsm_configfs.su_mutex),
> };
>
> +static int tsm_rtmr_register(const struct tsm_ops *ops)
> +{
> + struct config_group *rtmrs_group;
> +
> + lockdep_assert_held_write(&tsm_rwsem);
> +
> + if (!ops || !ops->capabilities.num_rtmrs)
> + return 0;
> +
> + if (ops->capabilities.num_rtmrs > TSM_MAX_RTMR)
> + return -EINVAL;
> +
> + tsm_rtmrs = kzalloc(sizeof(struct tsm_rtmrs_state), GFP_KERNEL);
> + if (!tsm_rtmrs)
> + return -ENOMEM;
> +
> + tsm_rtmrs->rtmrs = kcalloc(ops->capabilities.num_rtmrs,
> + sizeof(struct tsm_rtmr_state *),
> + GFP_KERNEL);
> + if (!tsm_rtmrs->rtmrs) {
> + kfree(tsm_rtmrs);
> + return -ENOMEM;
> + }
> +
> + rtmrs_group = configfs_register_default_group(&tsm_configfs.su_group, "rtmrs",
> + &tsm_rtmrs_type);
> + if (IS_ERR(rtmrs_group)) {
> + kfree(tsm_rtmrs->rtmrs);
> + kfree(tsm_rtmrs);
> + return PTR_ERR(rtmrs_group);
> + }
> +
> + tsm_rtmrs->group = rtmrs_group;
> +
> + return 0;
> +}
> +
> int tsm_register(const struct tsm_ops *ops, void *priv,
> const struct config_item_type *type)
> {
> const struct tsm_ops *conflict;
> + int rc;
>
> if (!type)
> type = &tsm_report_default_type;
> @@ -450,6 +590,10 @@ int tsm_register(const struct tsm_ops *ops, void *priv,
> return -EBUSY;
> }
>
> + rc = tsm_rtmr_register(ops);
> + if (rc < 0)
> + return rc;
> +
> provider.ops = ops;
> provider.data = priv;
> provider.type = type;
> @@ -457,11 +601,31 @@ int tsm_register(const struct tsm_ops *ops, void *priv,
> }
> EXPORT_SYMBOL_GPL(tsm_register);
>
> +static int tsm_rtmr_unregister(const struct tsm_ops *ops)
> +{
> + lockdep_assert_held_write(&tsm_rwsem);
> +
> + if ((ops) && (ops->capabilities.num_rtmrs > 0)) {
> + configfs_unregister_default_group(tsm_rtmrs->group);
> + kfree(tsm_rtmrs->rtmrs);
> + kfree(tsm_rtmrs);
> + }
> +
> + return 0;
> +}
> +
> int tsm_unregister(const struct tsm_ops *ops)
> {
> + int rc;
> +
> guard(rwsem_write)(&tsm_rwsem);
> if (ops != provider.ops)
> return -EBUSY;
> +
> + rc = tsm_rtmr_unregister(ops);
> + if (rc < 0)
> + return rc;
> +
> provider.ops = NULL;
> provider.data = NULL;
> provider.type = NULL;
> --
> 2.42.0
>

-- Regards, Mikko