[PATCH] arm64: fix missing syscall trace exit
From: Josh Stone <hidden>
Date: 2015-06-03 01:11:48
On 06/02/2015 06:01 PM, Josh Stone wrote:
quoted hunk ↗ jump to hunk
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. Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <redacted> Cc: Russell King <redacted> Signed-off-by: Josh Stone <redacted> --- arch/arm64/kernel/entry.S | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 959fe8733560..a547a3e8a198 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S@@ -608,7 +608,9 @@ ENDPROC(cpu_switch_to) */ ret_fast_syscall: 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, __sys_trace_return and x2, x1, #_TIF_WORK_MASK cbnz x2, fast_work_pending enable_step_tsk x1, x2
I do have one concern about this, also in Russell's ARM patch. Is it really ok to branch to __sys_trace_return with interrupts disabled? I didn't hit any issue from that, but my testcase only exercises this path once each run. So that might have just been lucky not to hit any gross scenario...