On Fri, Jun 26, 2026 at 04:31:47PM +0200, Christophe Leroy (CS GROUP) wrote:

Le 24/06/2026 à 19:15, Mukesh Kumar Chaurasiya (IBM) a écrit :

quoted

After enabling GENERIC_ENTRY on PowerPC, seccomp filters using
SCMP_ACT_ERRNO without an explicit errnoRet value return ENOSYS
(Function not implemented) instead of the expected EPERM (Operation
not permitted).

The issue occurs in system_call_exception() when syscall_enter_from_user_mode()
returns -1 to indicate the syscall should be skipped (e.g., blocked by seccomp).
The current code treats this -1 as a syscall number and compares it against
NR_syscalls. Since -1 (when cast to unsigned long) is greater than NR_syscalls,
the code incorrectly returns -ENOSYS, overwriting the errno that seccomp
already set via syscall_set_return_value().

The generic entry code in syscall_trace_enter() calls __secure_computing(),
which sets the appropriate errno in regs->gpr[3] and returns -1 to signal
that the syscall should be skipped. However, the PowerPC syscall handler
was not checking for this -1 return value before validating the syscall
number.

Fix this by explicitly checking if syscall_enter_from_user_mode() returns
-1 and returning the value already set in regs->gpr[3] (the errno from
seccomp) before performing the syscall number validation.

This aligns PowerPC's behavior with other architectures using GENERIC_ENTRY
and restores correct seccomp errno handling.

Fixes: bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature")
Reported-by: Michal Suchánek <redacted>

Closes: https://lore.kernel.org/all/ajpp-_XnbF3UTM_E@kunlun.suse.cz/ (local)

quoted

Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <redacted>
---
  arch/powerpc/kernel/syscall.c | 4 ++++
  1 file changed, 4 insertions(+)

diff --git a/arch/powerpc/kernel/syscall.c b/arch/powerpc/kernel/syscall.c
index a9da2af6efa8..5b58c8d396c8 100644
--- a/arch/powerpc/kernel/syscall.c
+++ b/arch/powerpc/kernel/syscall.c

@@ -22,6 +22,10 @@ notrace long system_call_exception(struct pt_regs *regs, unsigned long r0)
  	add_random_kstack_offset();
  	r0 = syscall_enter_from_user_mode(regs, r0);
+	/* Seccomp or ptrace may have set return value, skip syscall */
+	if (unlikely(r0 == -1L))

Is it really needed to add the L after 1 ?

I guess it's not needed, but syscall_trace_enter is returning -1L, and i
wanted to keep it consistent to that.

Regards,
Mukesh

quoted

+		return regs->gpr[3];
+
  	if (unlikely(r0 >= NR_syscalls)) {
  		if (unlikely(trap_is_unsupported_scv(regs))) {
  			/* Unsupported scv vector */