x86/pm: fix false positive kmemleak report in msr_build_context()

Since commit e2a1256 ("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 check wakeup_64.S file and __save/__restore_processor_state() if the struct is modified: it looks like it's the members before 'misc_enable' that must be carefully placed. 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 e2a1256 ("x86/speculation: Restore speculation related MSRs during S3 resume"). Others probably have the same issue since: commit 7a9c2dd ("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: 7a9c2dd ("x86/pm: Introduce quirk framework to save/restore extra MSR registers around suspend/resume") Closes: #268 Suggested-by: Mat Martineau <mathew.j.martineau@linux.intel.com> Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
multipath-tcp · Apr 26, 2022 · 0179baa · 0179baa
1 parent cfd7ded
commit 0179baa
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Showing 2 changed files with 9 additions and 5 deletions.
diff --git 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
@@ -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 before 'misc_enable', 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.
+ *
+ * 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) \