linux-kernel - Re: [PATCH 03/15] selftests/seccomp: mips: Define SYSCALL_NUM

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Date:   Fri, 18 Sep 2020 15:00:01 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     linux-kernel@...r.kernel.org,
        Thadeu Lima de Souza Cascardo <cascardo@...onical.com>,
        Max Filippov <jcmvbkbc@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Christian Brauner <christian@...uner.io>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>,
        linux-kselftest@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-xtensa@...ux-xtensa.org,
        linux-arm-kernel@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 03/15] selftests/seccomp: mips: Define SYSCALL_NUM_SET
 macro

On Tue, Sep 15, 2020 at 05:55:46PM +0200, Christian Brauner wrote:
> On Sat, Sep 12, 2020 at 04:08:08AM -0700, Kees Cook wrote:
> > Remove the mips special-case in change_syscall().
> > 
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > ---
> >  tools/testing/selftests/seccomp/seccomp_bpf.c | 17 +++++++++--------
> >  1 file changed, 9 insertions(+), 8 deletions(-)
> > 
> > diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
> > index 1c83e743bfb1..02a9a6599746 100644
> > --- a/tools/testing/selftests/seccomp/seccomp_bpf.c
> > +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
> > @@ -1742,6 +1742,13 @@ TEST_F(TRACE_poke, getpid_runs_normally)
> >  # define ARCH_REGS		struct pt_regs
> >  # define SYSCALL_NUM(_regs)	(_regs).regs[2]
> >  # define SYSCALL_SYSCALL_NUM	regs[4]
> > +# define SYSCALL_NUM_SET(_regs, _nr)			\
> > +	do {						\
> > +		if ((_regs).regs[2] == __NR_O32_Linux)	\
> > +			(_regs).regs[4] = _nr;		\
> > +		else					\
> > +			(_regs).regs[2] = _nr;		\
> > +	} while (0)
> 
> I think that
> 
> # define SYSCALL_NUM_SET(_regs, _nr)				\
> 	do {							\
> 		if (SYSCALL_NUM(_regs) == __NR_O32_Linux)	\
> 			(_regs).regs[4] = _nr;			\
> 		else						\
> 			(_regs).regs[2] = _nr;			\
> 	} while (0)
> 
> would read better but that's just a matter of taste. :)

That's how I started originally, but when I realized that I'd have to
reorganize SYSCALL_NUM() too, it seem best to have minimal churn, so I
left it open coded here, since that's how it needs to be in the end.

> Looks good!
> Acked-by: Christian Brauner <christian.brauner@...ntu.com>

Thanks for the reviews!

-- 
Kees Cook