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Date: Tue, 22 May 2012 15:48:40 -0500
Message-ID: <CABqD9haSh=Tof9n2m8PHBaoqac1kcUZq-f5BcjDBv++5APGTCg@mail.gmail.com>
Subject: Re: seccomp and ptrace. what is the correct order?
From: Will Drewry <wad@chromium.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>, Indan Zupancic <indan@nul.nu>,
        Roland McGrath <mcgrathr@google.com>,
        Eric Paris <netdev@parisplace.org>, linux-kernel@vger.kernel.org,
        linux-security-module@vger.kernel.org,
        kernel-hardening@lists.openwall.com, mingo@redhat.com, oleg@redhat.com,
        peterz@infradead.org, rdunlap@xenotime.net, tglx@linutronix.de,
        luto@mit.edu, eparis@redhat.com, serge.hallyn@canonical.com,
        pmoore@redhat.com, akpm@linux-foundation.org, corbet@lwn.net,
        eric.dumazet@gmail.com, markus@chromium.org, coreyb@linux.vnet.ibm.com,
        keescook@chromium.org
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On Tue, May 22, 2012 at 3:34 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> The proposed patch seems to duplicate the functionality in
> <asm/syscall.h>. ?Those macros also try to do the right thing in the
> presence of compat.

That was my first thought too, so I ran a few simple tests.  gcc isn't
smart enough to not add ~344 bytes of code to get the number and
arguments for the x86/kernel/ptrace.c case I included (in the
naive-est of integrations).  But I don't know that it justifies the
extra patchwork or enforcing shared code across arches.

Regardless, the syscall entry + trace code can use some attention
across the architectures. I don't know that
one-more-layer-of-abstraction is the right answer (rather than just
fixing the code). The biggest benefit would be having one-true
syscall_trace_entry slow path. That said, the fast paths will be
forever divergent so the opportunity for bugs like the ones pointed
out will still be there.

cheers!
will
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