From: Timothy E Baldwin <T.E.Baldwin99@members.leeds.ac.uk>

Date: Sat, 16 Jan 2021 15:18:54 +0000

Subject: arm64: ptrace: Fix seccomp of traced syscall -1 (NO_SYSCALL)

Git-commit: df84fe94708985cdfb78a83148322bcd0a699472

Patch-mainline: v5.12-rc1

References: git-fixes

Since commit f086f67485c5 ("arm64: ptrace: add support for syscall

emulation"), if system call number -1 is called and the process is being

traced with PTRACE_SYSCALL, for example by strace, the seccomp check is

skipped and -ENOSYS is returned unconditionally (unless altered by the

tracer) rather than carrying out action specified in the seccomp filter.

The consequence of this is that it is not possible to reliably strace

a seccomp based implementation of a foreign system call interface in

which r7/x8 is permitted to be -1 on entry to a system call.

Also trace_sys_enter and audit_syscall_entry are skipped if a system

call is skipped.

Fix by removing the in_syscall(regs) check restoring the previous

behaviour which is like AArch32, x86 (which uses generic code) and

everything else.

Cc: Oleg Nesterov <oleg@redhat.com>

Cc: Catalin Marinas<catalin.marinas@arm.com>

Cc: <stable@vger.kernel.org>

Fixes: f086f67485c5 ("arm64: ptrace: add support for syscall emulation")

Reviewed-by: Kees Cook <keescook@chromium.org>

Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>

Tested-by: Sudeep Holla <sudeep.holla@arm.com>

Signed-off-by: Timothy E Baldwin <T.E.Baldwin99@members.leeds.ac.uk>

Link: https://lore.kernel.org/r/90edd33b-6353-1228-791f-0336d94d5f8c@majoroak.me.uk

Signed-off-by: Will Deacon <will@kernel.org>

Signed-off-by: Mian Yousaf Kaukab <ykaukab@suse.de>

---

 arch/arm64/kernel/ptrace.c | 2 +-

 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c

index 3d5c8afca75b..170f42fd6101 100644

--- a/arch/arm64/kernel/ptrace.c

+++ b/arch/arm64/kernel/ptrace.c

@@ -1797,7 +1797,7 @@ int syscall_trace_enter(struct pt_regs *regs)

 	if (flags & (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE)) {

 		tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);

-		if (!in_syscall(regs) || (flags & _TIF_SYSCALL_EMU))

+		if (flags & _TIF_SYSCALL_EMU)

 			return NO_SYSCALL;

 	}

-- 

2.26.2