The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From df84fe94708985cdfb78a83148322bcd0a699472 Mon Sep 17 00:00:00 2001

From: Timothy E Baldwin T.E.Baldwin99@members.leeds.ac.uk Date: Sat, 16 Jan 2021 15:18:54 +0000 Subject: [PATCH] arm64: ptrace: Fix seccomp of traced syscall -1 (NO_SYSCALL)

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 Marinascatalin.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.u... Signed-off-by: Will Deacon will@kernel.org

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; }