[PATCH 5.17 308/772] x86/pm: Fix false positive kmemleak report in msr_build_context()

Greg Kroah-Hartman
2022-06-07T21:02:33Z

From: Matthieu Baerts <matthieu.baerts@tessares.net>

[ Upstream commit b0b592cf08367719e1d1ef07c9f136e8c17f7ec3 ]

Since

e2a1256b17b1 ("x86/speculation: Restore speculation related MSRs during S3 resume")

kmemleak reports this issue:

unreferenced object 0xffff888009cedc00 (size 256):
comm "swapper/0", pid 1, jiffies 4294693823 (age 73.764s)
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 48 00 00 00 00 00 00 00 ........H.......
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
backtrace:
msr_build_context (include/linux/slab.h:621)
pm_check_save_msr (arch/x86/power/cpu.c:520)
do_one_initcall (init/main.c:1298)
kernel_init_freeable (init/main.c:1370)
kernel_init (init/main.c:1504)
ret_from_fork (arch/x86/entry/entry_64.S:304)

Reproducer:

- boot the VM with a debug kernel config (see
https://github.com/multipath-tcp/mptcp_net-next/issues/268)
- wait ~1 minute
- start a kmemleak scan

The root cause here is alignment within the packed struct saved_context
(from suspend_64.h). Kmemleak only searches for pointers that are
aligned (see how pointers are scanned in kmemleak.c), but pahole shows
that the saved_msrs struct member and all members after it in the
structure are unaligned:

struct saved_context {
struct pt_regs regs; /* 0 168 */
/* --- cacheline 2 boundary (128 bytes) was 40 bytes ago --- */
u16 ds; /* 168 2 */

...

u64 misc_enable; /* 232 8 */
bool misc_enable_saved; /* 240 1 */

/* Note below odd offset values for the remainder of this struct */

struct saved_msrs saved_msrs; /* 241 16 */
/* --- cacheline 4 boundary (256 bytes) was 1 bytes ago --- */
long unsigned int efer; /* 257 8 */
u16 gdt_pad; /* 265 2 */
struct desc_ptr gdt_desc; /* 267 10 */
u16 idt_pad; /* 277 2 */
struct desc_ptr idt; /* 279 10 */
u16 ldt; /* 289 2 */
u16 tss; /* 291 2 */
long unsigned int tr; /* 293 8 */
long unsigned int safety; /* 301 8 */
long unsigned int return_address; /* 309 8 */

/* size: 317, cachelines: 5, members: 25 */
/* last cacheline: 61 bytes */
} __attribute__((__packed__));

Move misc_enable_saved to the end of the struct declaration so that
saved_msrs fits in before the cacheline 4 boundary.

The comment above the saved_context declaration says to fix wakeup_64.S
file and __save/__restore_processor_state() if the struct is modified:
it looks like all the accesses in wakeup_64.S are done through offsets
which are computed at build-time. Update that comment accordingly.

At the end, the false positive kmemleak report is due to a limitation
from kmemleak but it is always good to avoid unaligned members for
optimisation purposes.

Please note that it looks like this issue is not new, e.g.

https://lore.kernel.org/all/9f1bb619-c4ee-21c4-a251-870bd4db04fa@lwfinger.net/
https://lore.kernel.org/all/94e48fcd-1dbd-ebd2-4c91-f39941735909@molgen.mpg.de/

[ bp: Massage + cleanup commit message. ]

Fixes: 7a9c2dd08ead ("x86/pm: Introduce quirk framework to save/restore extra MSR registers around suspend/resume")
Suggested-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/r/20220426202138.498310-1-matthieu.baerts@tessares.net
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/include/asm/suspend_32.h | 2 +-
arch/x86/include/asm/suspend_64.h | 12 ++++++++----
2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/suspend_32.h b/arch/x86/include/asm/suspend_32.h
index 7b132d0312eb..a800abb1a992 100644
--- a/arch/x86/include/asm/suspend_32.h
+++ b/arch/x86/include/asm/suspend_32.h
@@ -19,7 +19,6 @@ struct saved_context {
u16 gs;
unsigned long cr0, cr2, cr3, cr4;
u64 misc_enable;
- bool misc_enable_saved;
struct saved_msrs saved_msrs;
struct desc_ptr gdt_desc;
struct desc_ptr idt;
@@ -28,6 +27,7 @@ struct saved_context {
unsigned long tr;
unsigned long safety;
unsigned long return_address;
+ bool misc_enable_saved;
} __attribute__((packed));

/* routines for saving/restoring kernel state */
diff --git a/arch/x86/include/asm/suspend_64.h b/arch/x86/include/asm/suspend_64.h
index 35bb35d28733..54df06687d83 100644
--- a/arch/x86/include/asm/suspend_64.h
+++ b/arch/x86/include/asm/suspend_64.h
@@ -14,9 +14,13 @@
* Image of the saved processor state, used by the low level ACPI suspend to
* RAM code and by the low level hibernation code.
*
- * If you modify it, fix arch/x86/kernel/acpi/wakeup_64.S and make sure that
- * __save/__restore_processor_state(), defined in arch/x86/kernel/suspend_64.c,
- * still work as required.
+ * If you modify it, check how it is used in arch/x86/kernel/acpi/wakeup_64.S
+ * and make sure that __save/__restore_processor_state(), defined in
+ * arch/x86/power/cpu.c, still work as required.
+ *
+ * Because the structure is packed, make sure to avoid unaligned members. For
+ * optimisation purposes but also because tools like kmemleak only search for
+ * pointers that are aligned.
*/
struct saved_context {
struct pt_regs regs;
@@ -36,7 +40,6 @@ struct saved_context {

unsigned long cr0, cr2, cr3, cr4;
u64 misc_enable;
- bool misc_enable_saved;
struct saved_msrs saved_msrs;
unsigned long efer;
u16 gdt_pad; /* Unused */
@@ -48,6 +51,7 @@ struct saved_context {
unsigned long tr;
unsigned long safety;
unsigned long return_address;
+ bool misc_enable_saved;
} __attribute__((packed));

#define loaddebug(thread,register) \
--
2.35.1