Re: [PATCH] riscv: return -ENOSYS for syscall -1

Christoph Hellwig
2020-12-23T08:24:16Z

On Tue, Dec 22, 2020 at 09:22:19AM -0700, Tycho Andersen wrote:
> On Mon, Dec 21, 2020 at 11:52:00PM +0100, Andreas Schwab wrote:
> > Properly return -ENOSYS for syscall -1 instead of leaving the return value
> > uninitialized. This fixes the strace teststuite.
> >
> > Fixes: 5340627e3fe0 ("riscv: add support for SECCOMP and SECCOMP_FILTER")
> > Signed-off-by: Andreas Schwab <schwab@suse.de>
> > ---
> > arch/riscv/kernel/entry.S | 9 +--------
> > 1 file changed, 1 insertion(+), 8 deletions(-)
> >
> > diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> > index 524d918f3601..d07763001eb0 100644
> > --- a/arch/riscv/kernel/entry.S
> > +++ b/arch/riscv/kernel/entry.S
> > @@ -186,14 +186,7 @@ check_syscall_nr:
> > * Syscall number held in a7.
> > * If syscall number is above allowed value, redirect to ni_syscall.
> > */
> > - bge a7, t0, 1f
> > - /*
> > - * Check if syscall is rejected by tracer, i.e., a7 == -1.
> > - * If yes, we pretend it was executed.
> > - */
> > - li t1, -1
> > - beq a7, t1, ret_from_syscall_rejected
> > - blt a7, t1, 1f
> > + bgeu a7, t0, 1f
>
> IIUC, this is all dead code anyway for the path where seccomp actually
> rejects the syscall, since it should do the rejection directly in
> handle_syscall_trace_enter(), which is called above this hunk. So it
> seems good to me.

That change really needs to be documented in the commit log, or even
better split into a separate patch (still documented of course!).