| Message ID | 1528371125-24505-1-git-send-email-Dave.Martin@arm.com |
|---|---|
| State | New |
| Headers | show |
| Series | arm64: Fix syscall restarting around signal suppressed by tracer | expand |
On Thu, Jun 07, 2018 at 12:32:05PM +0100, Dave P Martin wrote: > Commit 17c2895 ("arm64: Abstract syscallno manipulation") abstracts > out the pt_regs.syscallno value for a syscall cancelled by a tracer > as NO_SYSCALL, and provides helpers to set and check for this > condition. However, the way this was implemented has the > unintended side-effect of disabling part of the syscall restart > logic. > > This comes about because the second in_syscall() check in > do_signal() re-evaluates the "in a syscall" condition based on the > updated pt_regs instead of the original pt_regs. forget_syscall() > is explicitly called prior to the second check in order to prevent > restart logic in the ret_to_user path being spuriously triggered, > which means that the second in_syscall() check always yields false. > > This triggers a failure in > tools/testing/selftests/seccomp/seccomp_bpf.c, when using ptrace to > suppress a signal that interrups a nanosleep() syscall. > > Misbehaviour of this type is only expected in the case where a > tracer suppresses a signal and the target process is either being > single-stepped or the interrupted syscall attempts to restart via > -ERESTARTBLOCK. > > This patch restores the old behaviour by performing the > in_syscall() check only once at the start of the function. > > Fixes: 17c289586009 ("arm64: Abstract syscallno manipulation") > Signed-off-by: Dave Martin <Dave.Martin@arm.com> > Reported-by: Sumit Semwal <sumit.semwal@linaro.org> > Cc: Will Deacon <will.deacon@arm.com> > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: <stable@vger.kernel.org> # 4.14.x- Applied. Thanks. -- Catalin
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c index 154b7d3..f212090 100644 --- a/arch/arm64/kernel/signal.c +++ b/arch/arm64/kernel/signal.c @@ -830,11 +830,12 @@ static void do_signal(struct pt_regs *regs) unsigned long continue_addr = 0, restart_addr = 0; int retval = 0; struct ksignal ksig; + bool syscall = in_syscall(regs); /* * If we were from a system call, check for system call restarting... */ - if (in_syscall(regs)) { + if (syscall) { continue_addr = regs->pc; restart_addr = continue_addr - (compat_thumb_mode(regs) ? 2 : 4); retval = regs->regs[0]; @@ -886,7 +887,7 @@ static void do_signal(struct pt_regs *regs) * Handle restarting a different system call. As above, if a debugger * has chosen to restart at a different PC, ignore the restart. */ - if (in_syscall(regs) && regs->pc == restart_addr) { + if (syscall && regs->pc == restart_addr) { if (retval == -ERESTART_RESTARTBLOCK) setup_restart_syscall(regs); user_rewind_single_step(current);
Commit 17c2895 ("arm64: Abstract syscallno manipulation") abstracts out the pt_regs.syscallno value for a syscall cancelled by a tracer as NO_SYSCALL, and provides helpers to set and check for this condition. However, the way this was implemented has the unintended side-effect of disabling part of the syscall restart logic. This comes about because the second in_syscall() check in do_signal() re-evaluates the "in a syscall" condition based on the updated pt_regs instead of the original pt_regs. forget_syscall() is explicitly called prior to the second check in order to prevent restart logic in the ret_to_user path being spuriously triggered, which means that the second in_syscall() check always yields false. This triggers a failure in tools/testing/selftests/seccomp/seccomp_bpf.c, when using ptrace to suppress a signal that interrups a nanosleep() syscall. Misbehaviour of this type is only expected in the case where a tracer suppresses a signal and the target process is either being single-stepped or the interrupted syscall attempts to restart via -ERESTARTBLOCK. This patch restores the old behaviour by performing the in_syscall() check only once at the start of the function. Fixes: 17c289586009 ("arm64: Abstract syscallno manipulation") Signed-off-by: Dave Martin <Dave.Martin@arm.com> Reported-by: Sumit Semwal <sumit.semwal@linaro.org> Cc: Will Deacon <will.deacon@arm.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: <stable@vger.kernel.org> # 4.14.x- --- arch/arm64/kernel/signal.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) -- 2.1.4