linux-kernel - [PATCH] ACPI: sysfs: Fix pm_profile

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Message-Id: <20200612045149.1837-1-natechancellor@gmail.com>
Date:   Thu, 11 Jun 2020 21:51:50 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>
Cc:     linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Kees Cook <keescook@...omium.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        yuu ichii <byahu140@...sei.be>
Subject: [PATCH] ACPI: sysfs: Fix pm_profile_attr type

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@...sei.be>
Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
---
 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
-- 
2.27.0