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authorLinus Torvalds <torvalds@linux-foundation.org>2012-02-16 19:11:15 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2012-02-16 19:11:15 -0800
commit4903062b5485f0e2c286a23b44c9b59d9b017d53 (patch)
treec521dd28c5aa409dcd76ca8a522886fa3c272a31 /arch/x86/include
parentb3b0870ef3ffed72b92415423da864f440f57ad6 (diff)
i387: move AMD K7/K8 fpu fxsave/fxrstor workaround from save to restore
The AMD K7/K8 CPUs don't save/restore FDP/FIP/FOP unless an exception is pending. In order to not leak FIP state from one process to another, we need to do a floating point load after the fxsave of the old process, and before the fxrstor of the new FPU state. That resets the state to the (uninteresting) kernel load, rather than some potentially sensitive user information. We used to do this directly after the FPU state save, but that is actually very inconvenient, since it (a) corrupts what is potentially perfectly good FPU state that we might want to lazy avoid restoring later and (b) on x86-64 it resulted in a very annoying ordering constraint, where "__unlazy_fpu()" in the task switch needs to be delayed until after the DS segment has been reloaded just to get the new DS value. Coupling it to the fxrstor instead of the fxsave automatically avoids both of these issues, and also ensures that we only do it when actually necessary (the FP state after a save may never actually get used). It's simply a much more natural place for the leaked state cleanup. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'arch/x86/include')
-rw-r--r--arch/x86/include/asm/i387.h19
1 files changed, 0 insertions, 19 deletions
diff --git a/arch/x86/include/asm/i387.h b/arch/x86/include/asm/i387.h
index 86974c72d0d0..01b115d86770 100644
--- a/arch/x86/include/asm/i387.h
+++ b/arch/x86/include/asm/i387.h
@@ -211,15 +211,6 @@ static inline void fpu_fxsave(struct fpu *fpu)
#endif /* CONFIG_X86_64 */
-/* We need a safe address that is cheap to find and that is already
- in L1 during context switch. The best choices are unfortunately
- different for UP and SMP */
-#ifdef CONFIG_SMP
-#define safe_address (__per_cpu_offset[0])
-#else
-#define safe_address (__get_cpu_var(kernel_cpustat).cpustat[CPUTIME_USER])
-#endif
-
/*
* These must be called with preempt disabled
*/
@@ -243,16 +234,6 @@ static inline void fpu_save_init(struct fpu *fpu)
if (unlikely(fpu->state->fxsave.swd & X87_FSW_ES))
asm volatile("fnclex");
-
- /* AMD K7/K8 CPUs don't save/restore FDP/FIP/FOP unless an exception
- is pending. Clear the x87 state here by setting it to fixed
- values. safe_address is a random variable that should be in L1 */
- alternative_input(
- ASM_NOP8 ASM_NOP2,
- "emms\n\t" /* clear stack tags */
- "fildl %P[addr]", /* set F?P to defined value */
- X86_FEATURE_FXSAVE_LEAK,
- [addr] "m" (safe_address));
}
static inline void __save_init_fpu(struct task_struct *tsk)