On Mon, May 18, 2020 at 12:41:20PM +0100, Will Deacon wrote: > 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 <[email protected]> > > --- > > 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 <[email protected]> > > Also needs: > > Cc: <[email protected]> > Fixes: f086f67485c5 ("arm64: ptrace: add support for syscall emulation") > > Catalin -- can you pick this up for 5.7 please, with my 'nit' addressed?
I'll queue it with the above addressed. I think flags also needs to be unsigned long rather than u32. However, before sending the pull request, I'd like Sudeep to confirm that it doesn't break his original use-case for this feature. -- Catalin
