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(-)

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);