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

commit df84fe94708985cdfb78a83148322bcd0a699472 upstream.

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 30b877f8b85ef28104a33a9d4f3d81bb6855ac21..0cfd685774891eed8abd9a1f7e8c8d8583b136cd 100644 (file)
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -1844,7 +1844,7 @@ 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 -1;
        }