Re: [PATCH v2 1/2] ptrace: PTRACE_SET_SYSCALL_INFO syscall skipping support

[Thomas Bogendoerfer <tsbogend@alpha.franken.de>]

On Tue, Jul 07, 2026 at 06:04:56PM +0200, Oleg Nesterov wrote:
> On 07/07, Renzo Davoli wrote:
> >
> > On Sun, Jul 05, 2026 at 04:38:05PM +0200, Oleg Nesterov wrote:
> > > OK, lets only allow the _SECCOMP -> _EXIT transition for now.
> > done in v3.
> > > But will it work on MIPS?
> >
> > IMHO yes, it will (would).
> 
> Agreed, it is not that I think it won't... but it would be nice to have an ACK
> from arch/mips maintainers. syscall_trace_enter() is called from MIPS asm code
> which I obviously can't understand.

current code works for SECCOMP and with below untested change it should
work for PTRACE_SYSCALL, too.

Thomas.

diff --git a/arch/mips/kernel/ptrace.c b/arch/mips/kernel/ptrace.c
index 3f4c94c88124..87102a03b6ea 100644
--- a/arch/mips/kernel/ptrace.c
+++ b/arch/mips/kernel/ptrace.c
@@ -1321,8 +1321,12 @@ long arch_ptrace(struct task_struct *child, long request,
  */
 asmlinkage long syscall_trace_enter(struct pt_regs *regs)
 {
+	long syscall;
+
 	user_exit();
 
+	syscall = current_thread_info()->syscall;
+
 	if (test_thread_flag(TIF_SYSCALL_TRACE)) {
 		if (ptrace_report_syscall_entry(regs))
 			return -1;
@@ -1342,7 +1346,7 @@ asmlinkage long syscall_trace_enter(struct pt_regs *regs)
 	 * Negative syscall numbers are mistaken for rejected syscalls, but
 	 * won't have had the return value set appropriately, so we do so now.
 	 */
-	if (current_thread_info()->syscall < 0)
+	if (syscall < 0)
 		syscall_set_return_value(current, regs, -ENOSYS, 0);
 	return current_thread_info()->syscall;
 }

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]