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Commit b3494a4a authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar
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x86/asm/entry: Check for syscall exit work with IRQs disabled 



We currently have a race: if we're preempted during syscall
exit, we can fail to process syscall return work that is queued
up while we're preempted in ret_from_sys_call after checking
ti.flags.

Fix it by disabling interrupts before checking ti.flags.

Reported-by: default avatarStefan Seyfried <stefan.seyfried@googlemail.com>
Reported-by: default avatarTakashi Iwai <tiwai@suse.de>
Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Acked-by: default avatarDenys Vlasenko <dvlasenk@redhat.com>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Fixes: 96b6352c ("x86_64, entry: Remove the syscall exit audit")
Link: http://lkml.kernel.org/r/189320d42b4d671df78c10555976bb10af1ffc75.1427137498.git.luto@kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent bc465aa9

arch/x86/kernel/entry_64.S

+14 −4
Original line number Diff line number Diff line
@@ -364,12 +364,21 @@ system_call_fastpath: 
 * Has incomplete stack frame and undefined top of stack.

 */

ret_from_sys_call:

	testl $_TIF_ALLWORK_MASK,TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET)

	jnz int_ret_from_sys_call_fixup	/* Go the the slow path */



	LOCKDEP_SYS_EXIT

	DISABLE_INTERRUPTS(CLBR_NONE)

	TRACE_IRQS_OFF



	/*

	 * We must check ti flags with interrupts (or at least preemption)

	 * off because we must *never* return to userspace without

	 * processing exit work that is enqueued if we're preempted here.

	 * In particular, returning to userspace with any of the one-shot

	 * flags (TIF_NOTIFY_RESUME, TIF_USER_RETURN_NOTIFY, etc) set is

	 * very bad.

	 */

	testl $_TIF_ALLWORK_MASK,TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET)

	jnz int_ret_from_sys_call_fixup	/* Go the the slow path */



	CFI_REMEMBER_STATE

	/*

	 * sysretq will re-enable interrupts:
@@ -386,7 +395,7 @@ ret_from_sys_call: 


int_ret_from_sys_call_fixup:

	FIXUP_TOP_OF_STACK %r11, -ARGOFFSET

	jmp int_ret_from_sys_call

	jmp int_ret_from_sys_call_irqs_off



	/* Do syscall tracing */

tracesys:
@@ -432,6 +441,7 @@ tracesys_phase2: 
GLOBAL(int_ret_from_sys_call)

	DISABLE_INTERRUPTS(CLBR_NONE)

	TRACE_IRQS_OFF

int_ret_from_sys_call_irqs_off:

	movl $_TIF_ALLWORK_MASK,%edi

	/* edi:	mask to check */

GLOBAL(int_with_check)