Messages in this thread Patch in this message | | | From | Matthieu Baerts <> | Subject | [PATCH v3] x86/pm: fix false positive kmemleak report in msr_build_context() | Date | Tue, 26 Apr 2022 22:21:37 +0200 |
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Since commit 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)
It is easy to reproduce it on my side:
- boot the VM with a debug kernel config (see the 'Closes:' tag) - wait ~1 minute - start a kmemleak scan
It seems kmemleak has an issue with the array allocated in msr_build_context(). This array is assigned to a pointer in a static structure (saved_context.saved_msrs->array): there is no leak then.
A simple fix for this issue would be to use kmemleak_no_leak() but Mat noticed that 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 */ u16 es; /* 170 2 */ u16 fs; /* 172 2 */ u16 gs; /* 174 2 */ long unsigned int kernelmode_gs_base; /* 176 8 */ long unsigned int usermode_gs_base; /* 184 8 */ /* --- cacheline 3 boundary (192 bytes) --- */ long unsigned int fs_base; /* 192 8 */ long unsigned int cr0; /* 200 8 */ long unsigned int cr2; /* 208 8 */ long unsigned int cr3; /* 216 8 */ long unsigned int cr4; /* 224 8 */ 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__));
By moving 'misc_enable_saved' to the end of the struct declaration, 'saved_msrs' fits in before the cacheline 4 boundary and the kmemleak warning goes away.
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. This comment has been updated accordingly.
At the end, the false positive kmemleak report is due to a limitation from kmemleak but that's always good to avoid unaligned member 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/
But on my side, msr_build_context() is only used since:
commit e2a1256b17b1 ("x86/speculation: Restore speculation related MSRs during S3 resume").
Others probably have the same issue since:
commit 7a9c2dd08ead ("x86/pm: Introduce quirk framework to save/restore extra MSR registers around suspend/resume"),
Hence the 'Fixes' tag here below to help with the backports.
Fixes: 7a9c2dd08ead ("x86/pm: Introduce quirk framework to save/restore extra MSR registers around suspend/resume") Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/268 Suggested-by: Mat Martineau <mathew.j.martineau@linux.intel.com> Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net> ---
Notes: v3: - update the comment above 'saved_context' structure (Borislav) v2: - update 'saved_context' structure instead of using kmemleak_no_leak() (Mat)
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..0dc400fae1b2 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 + * optimisations 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) \ -- 2.34.1
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