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x86/entry/64/compat: After SYSENTER, move STI after the NT fixup

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We eventually want to make it all the way into C code before
enabling interrupts.  We need to rework our flags handling
slightly to delay enabling interrupts.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/35d24d2a9305da3182eab7b2cdfd32902e90962c.1444091584.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski 2015-10-05 17:47:55 -07:00 committed by Ingo Molnar
parent 72f924783b
commit b611acf473
1 changed files with 22 additions and 8 deletions
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30
arch/x86/entry/entry_64_compat.S
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@ -58,14 +58,9 @@ ENDPROC(native_usergs_sysret32)
* with the int 0x80 path.
*/
ENTRY(entry_SYSENTER_compat)
/*
* Interrupts are off on entry.
* We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
* it is too small to ever cause noticeable irq latency.
*/
/* Interrupts are off on entry. */
SWAPGS_UNSAFE_STACK
movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
ENABLE_INTERRUPTS(CLBR_NONE)
/* Zero-extending 32-bit regs, do not remove */
movl %ebp, %ebp
@ -76,7 +71,16 @@ ENTRY(entry_SYSENTER_compat)
/* Construct struct pt_regs on stack */
pushq $__USER32_DS /* pt_regs->ss */
pushq %rbp /* pt_regs->sp */
pushfq /* pt_regs->flags */
/*
* Push flags. This is nasty. First, interrupts are currently
* off, but we need pt_regs->flags to have IF set. Second, even
* if TF was set when SYSENTER started, it's clear by now. We fix
* that later using TIF_SINGLESTEP.
*/
pushfq /* pt_regs->flags (except IF = 0) */
orl $X86_EFLAGS_IF, (%rsp) /* Fix saved flags */
pushq $__USER32_CS /* pt_regs->cs */
pushq %r10 /* pt_regs->ip = thread_info->sysenter_return */
pushq %rax /* pt_regs->orig_ax */
@ -92,11 +96,21 @@ ENTRY(entry_SYSENTER_compat)
* Sysenter doesn't filter flags, so we need to clear NT
* ourselves. To save a few cycles, we can check whether
* NT was set instead of doing an unconditional popfq.
* This needs to happen before enabling interrupts so that
* we don't get preempted with NT set.
*/
testl $X86_EFLAGS_NT, EFLAGS(%rsp)
jnz sysenter_fix_flags
sysenter_flags_fixed:
/*
* Re-enable interrupts. IRQ tracing already thinks that IRQs are
* on (since we treat user mode as having IRQs on), and the
* prologue above is too short for it to be worth adding a
* tracing round trip.
*/
ENABLE_INTERRUPTS(CLBR_NONE)
/*
* No need to do an access_ok() check here because RBP has been
* 32-bit zero extended:
@ -244,7 +258,7 @@ sysexit_audit:
#endif
sysenter_fix_flags:
pushq $(X86_EFLAGS_IF|X86_EFLAGS_FIXED)
pushq $X86_EFLAGS_FIXED
popfq
jmp sysenter_flags_fixed