On Fri, May 15, 2020 at 06:22:53PM -0400, Keno Fischer wrote:
> Quoth the man page:
> ```
> If the tracee was restarted by PTRACE_SYSCALL or PTRACE_SYSEMU, the
> tracee enters syscall-enter-stop just prior to entering any system
> call (which will not be executed if the restart was using
> PTRACE_SYSEMU, regardless of any change made to registers at this
> point or how the tracee is restarted after this stop).
> ```
>
> The parenthetical comment is currently true on x86 and powerpc,
> but not currently true on arm64. arm64 re-checks the _TIF_SYSCALL_EMU
> flag after the syscall entry ptrace stop. However, at this point,
> it reflects which method was used to re-start the syscall
> at the entry stop, rather than the method that was used to reach it.
> Fix that by recording the original flag before performing the ptrace
> stop, bringing the behavior in line with documentation and x86/powerpc.
>
> Signed-off-by: Keno Fischer <k...@juliacomputing.com>
> ---
> arch/arm64/kernel/ptrace.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
> index b3d3005d9515..b67b4d14aa17 100644
> --- a/arch/arm64/kernel/ptrace.c
> +++ b/arch/arm64/kernel/ptrace.c
> @@ -1829,10 +1829,12 @@ static void tracehook_report_syscall(struct pt_regs
> *regs,
>
> int syscall_trace_enter(struct pt_regs *regs)
> {
> - if (test_thread_flag(TIF_SYSCALL_TRACE) ||
> - test_thread_flag(TIF_SYSCALL_EMU)) {
> + u32 flags = READ_ONCE(current_thread_info()->flags) &
> + (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE);
> +
> + if (flags) {
nit: but I'd rather the '&' operation was in the conditional so that the
'flags' variable holds all of the flags.
With that:
Acked-by: Will Deacon <w...@kernel.org>
Also needs:
Cc: <sta...@vger.kernel.org>
Fixes: f086f67485c5 ("arm64: ptrace: add support for syscall emulation")
Catalin -- can you pick this up for 5.7 please, with my 'nit' addressed?
Will
