Commit b611acf4 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar
Browse files

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



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: default avatarAndy 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: default avatarIngo Molnar <mingo@kernel.org>
parent 72f92478

arch/x86/entry/entry_64_compat.S

+22 −8
Original line number Diff line number Diff line
@@ -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

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