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 :
> > 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 <[email protected]>
>
> Closes: https://lore.kernel.org/all/[email protected]/
>
> > Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <[email protected]>
> > ---
> > 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
> > + return regs->gpr[3];
> > +
> > if (unlikely(r0 >= NR_syscalls)) {
> > if (unlikely(trap_is_unsupported_scv(regs))) {
> > /* Unsupported scv vector */
>
