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| author |   Thomas Gleixner <tglx@linutronix.de> | 2019-11-16 11:12:03 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2019-11-16 11:24:07 +0100 |
| commit | a3ba966066afbe8fd0d3605ffe04c633083752f1 (patch) | |
| tree | 46b9571c5a35456ec64e3aa012d217da253435e0 /arch/x86/entry | |
| parent | selftests/x86/iopl: Extend test to cover IOPL emulation (diff) | |
| download | linux-dev-a3ba966066afbe8fd0d3605ffe04c633083752f1.tar.xz linux-dev-a3ba966066afbe8fd0d3605ffe04c633083752f1.zip | |
x86/entry/32: Clarify register saving in __switch_to_asm()
commit 6690e86be83a ("sched/x86: Save [ER]FLAGS on context switch")
re-introduced the flags saving on context switch to prevent AC leakage.
The pushf/popf instructions are right among the callee saved register
section, so the comment explaining the save/restore is not entirely
correct.
Add a seperate comment to pushf/popf explaining the reason.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'arch/x86/entry')
| -rw-r--r-- | arch/x86/entry/entry_32.S | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index f83ca5aa8b77..99fad6fed03c 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -718,6 +718,11 @@ ENTRY(__switch_to_asm) pushl %ebx pushl %edi pushl %esi + /* + * Flags are saved to prevent AC leakage. This could go + * away if objtool would have 32bit support to verify + * the STAC/CLAC correctness. + */ pushfl /* switch stack */ @@ -740,8 +745,9 @@ ENTRY(__switch_to_asm) FILL_RETURN_BUFFER %ebx, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW #endif - /* restore callee-saved registers */ + /* Restore flags or the incoming task to restore AC state. */ popfl + /* restore callee-saved registers */ popl %esi popl %edi popl %ebx |