Re: [PATCH 2/6] x86: Enable seccomp architecture tracking

On Thu, Sep 24, 2020 at 02:45:45AM +0200, Jann Horn wrote:

On Thu, Sep 24, 2020 at 1:29 AM Kees Cook [off-list ref] wrote:

quoted

Provide seccomp internals with the details to calculate which syscall
table the running kernel is expecting to deal with. This allows for
efficient architecture pinning and paves the way for constant-action
bitmaps.

[...]

quoted

diff --git a/arch/x86/include/asm/seccomp.h b/arch/x86/include/asm/seccomp.h

[...]

quoted

+#ifdef CONFIG_X86_64

[...]

quoted

+#else /* !CONFIG_X86_64 */
+# define SECCOMP_ARCH                                  AUDIT_ARCH_I386
+#endif

If we are on a 32-bit kernel, performing architecture number checks in
the kernel is completely pointless, because we know that there is only
a single architecture identifier under which syscalls can happen.

While this patch is useful for enabling the bitmap logic in the
following patches, I think it adds unnecessary overhead in the context
of the previous patch.

That's what the RFC was trying to do (avoid the logic if there is only a
single arch known to the kernel). I will rework this a bit harder. :)

-- 
Kees Cook