Messages in this thread | | | Date | Mon, 18 May 2020 12:41:20 +0100 | From | Will Deacon <> | Subject | Re: [PATCH] arm64: Fix PTRACE_SYSEMU semantics |
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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 <keno@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 <will@kernel.org>
Also needs:
Cc: <stable@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
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