On Friday, June 12, 2020 6:51:50 AM CEST Nathan Chancellor wrote:
> When running a kernel with Clang's Control Flow Integrity implemented,
> there is a violation that happens when accessing
> /sys/firmware/acpi/pm_profile:
>
> $ cat /sys/firmware/acpi/pm_profile
> 0
>
> $ dmesg
> ...
> [ 17.352564] ------------[ cut here ]------------
> [ 17.352568] CFI failure (target: acpi_show_profile+0x0/0x8):
> [ 17.352572] WARNING: CPU: 3 PID: 497 at kernel/cfi.c:29 __cfi_check_fail+0x33/0x40
> [ 17.352573] Modules linked in:
> [ 17.352575] CPU: 3 PID: 497 Comm: cat Tainted: G W 5.7.0-microsoft-standard+ #1
> [ 17.352576] RIP: 0010:__cfi_check_fail+0x33/0x40
> [ 17.352577] Code: 48 c7 c7 50 b3 85 84 48 c7 c6 50 0a 4e 84 e8 a4 d8 60 00 85 c0 75 02 5b c3 48 c7 c7 dc 5e 49 84 48 89 de 31 c0 e8 7d 06 eb ff <0f> 0b 5b c3 00 00 cc cc 00 00 cc cc 00 85 f6 74 25 41 b9 ea ff ff
> [ 17.352577] RSP: 0018:ffffaa6dc3c53d30 EFLAGS: 00010246
> [ 17.352578] RAX: 331267e0c06cee00 RBX: ffffffff83d85890 RCX: ffffffff8483a6f8
> [ 17.352579] RDX: ffff9cceabbb37c0 RSI: 0000000000000082 RDI: ffffffff84bb9e1c
> [ 17.352579] RBP: ffffffff845b2bc8 R08: 0000000000000001 R09: ffff9cceabbba200
> [ 17.352579] R10: 000000000000019d R11: 0000000000000000 R12: ffff9cc947766f00
> [ 17.352580] R13: ffffffff83d6bd50 R14: ffff9ccc6fa80000 R15: ffffffff845bd328
> [ 17.352582] FS: 00007fdbc8d13580(0000) GS:ffff9cce91ac0000(0000) knlGS:0000000000000000
> [ 17.352582] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 17.352583] CR2: 00007fdbc858e000 CR3: 00000005174d0000 CR4: 0000000000340ea0
> [ 17.352584] Call Trace:
> [ 17.352586] ? rev_id_show+0x8/0x8
> [ 17.352587] ? __cfi_check+0x45bac/0x4b640
> [ 17.352589] ? kobj_attr_show+0x73/0x80
> [ 17.352590] ? sysfs_kf_seq_show+0xc1/0x140
> [ 17.352592] ? ext4_seq_options_show.cfi_jt+0x8/0x8
> [ 17.352593] ? seq_read+0x180/0x600
> [ 17.352595] ? sysfs_create_file_ns.cfi_jt+0x10/0x10
> [ 17.352596] ? tlbflush_read_file+0x8/0x8
> [ 17.352597] ? __vfs_read+0x6b/0x220
> [ 17.352598] ? handle_mm_fault+0xa23/0x11b0
> [ 17.352599] ? vfs_read+0xa2/0x130
> [ 17.352599] ? ksys_read+0x6a/0xd0
> [ 17.352601] ? __do_sys_getpgrp+0x8/0x8
> [ 17.352602] ? do_syscall_64+0x72/0x120
> [ 17.352603] ? entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [ 17.352604] ---[ end trace 7b1fa81dc897e419 ]---
>
> When /sys/firmware/acpi/pm_profile is read, sysfs_kf_seq_show is called,
> which in turn calls kobj_attr_show, which gets the ->show callback
> member by calling container_of on attr (casting it to struct
> kobj_attribute) then calls it.
>
> There is a CFI violation because pm_profile_attr is of type
> struct device_attribute but kobj_attr_show calls ->show expecting it
> to be from struct kobj_attribute. CFI checking ensures that function
> pointer types match when doing indirect calls. Fix pm_profile_attr to
> be defined in terms of kobj_attribute so there is no violation or
> mismatch.
>
> Fixes: 362b646062b2 ("ACPI: Export FADT pm_profile integer value to userspace")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1051
> Reported-by: yuu ichii <byahu140@xxxxxxxxx>
> Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
> ---
> drivers/acpi/sysfs.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/acpi/sysfs.c b/drivers/acpi/sysfs.c
> index 3a89909b50a6..76c668c05fa0 100644
> --- a/drivers/acpi/sysfs.c
> +++ b/drivers/acpi/sysfs.c
> @@ -938,13 +938,13 @@ static void __exit interrupt_stats_exit(void)
> }
>
> static ssize_t
> -acpi_show_profile(struct device *dev, struct device_attribute *attr,
> +acpi_show_profile(struct kobject *kobj, struct kobj_attribute *attr,
> char *buf)
> {
> return sprintf(buf, "%d\n", acpi_gbl_FADT.preferred_profile);
> }
>
> -static const struct device_attribute pm_profile_attr =
> +static const struct kobj_attribute pm_profile_attr =
> __ATTR(pm_profile, S_IRUGO, acpi_show_profile, NULL);
>
> static ssize_t hotplug_enabled_show(struct kobject *kobj,
>
> base-commit: b791d1bdf9212d944d749a5c7ff6febdba241771
>
Applied as 5.8-rc material, thanks!
