Commit 04d7e098 authored Jun 05, 2015 by Josh Stone Committed by Catalin Marinas Jun 08, 2015

arm64: fix missing syscall trace exit



If a syscall is entered without TIF_SYSCALL_TRACE set, then it goes on
the fast path.  It's then possible to have TIF_SYSCALL_TRACE added in
the middle of the syscall, but ret_fast_syscall doesn't check this flag
again.  This causes a ptrace syscall-exit-stop to be missed.

For instance, from a PTRACE_EVENT_FORK reported during do_fork, the
tracer might resume with PTRACE_SYSCALL, setting TIF_SYSCALL_TRACE.
Now the completion of the fork should have a syscall-exit-stop.

Russell King fixed this on arm by re-checking _TIF_SYSCALL_WORK in the
fast exit path.  Do the same on arm64.

Reviewed-by: Will Deacon <will.deacon@arm.com>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Josh Stone <jistone@redhat.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

parent addc8120

arch/arm64/kernel/entry.S

+6 −1

Original line number	Original line	Diff line number	Diff line
	@@ -611,11 +611,16 @@ ENDPROC(cpu_switch_to)
	*/		*/
	ret_fast_syscall:		ret_fast_syscall:
	disable_irq // disable interrupts		disable_irq // disable interrupts
	ldr x1, [tsk, #TI_FLAGS]		ldr x1, [tsk, #TI_FLAGS] // re-check for syscall tracing
			and x2, x1, #_TIF_SYSCALL_WORK
			cbnz x2, ret_fast_syscall_trace
	and x2, x1, #_TIF_WORK_MASK		and x2, x1, #_TIF_WORK_MASK
	cbnz x2, fast_work_pending		cbnz x2, fast_work_pending
	enable_step_tsk x1, x2		enable_step_tsk x1, x2
	kernel_exit 0, ret = 1		kernel_exit 0, ret = 1
			ret_fast_syscall_trace:
			enable_irq // enable interrupts
			b __sys_trace_return

	/*		/*
	* Ok, we need to do extra processing, enter the slow path.		* Ok, we need to do extra processing, enter the slow path.