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From: Paul Moore <paul@paul-moore.com>
To: "Thomas Weißschuh" <linux@weissschuh.net>
Cc: linux-audit@redhat.com, bpf@vger.kernel.org
Subject: Re: AUDIT_ARCH_ and __NR_syscall constants for seccomp filters
Date: Mon, 28 Jun 2021 12:59:53 -0400	[thread overview]
Message-ID: <CAHC9VhSTb75NEPZRm+Tkngv=SW8ntmSpVCrXMHHHWc2qYNZqCA@mail.gmail.com> (raw)
In-Reply-To: <0b926f59-464d-4b67-8f32-329cf9695cf7@t-8ch.de>

On Mon, Jun 28, 2021 at 9:25 AM Thomas Weißschuh <linux@weissschuh.net> wrote:
>
> Hi everyone,
>
> there does not seem to be a way to access the AUDIT_ARCH_ constant that matches
> the currently visible syscall numbers (__NR_...) from the kernel uapi headers.

Looking at Linus' current tree I see the AUDIT_ARCH_* defines in
include/uapi/linux/audit.h; looking on my system right now I see the
defines in /usr/include/linux/audit.h.  What kernel repository and
distribution are you using?

> Questions:
>
> Is it really necessary to validate the arch value when syscall numbers are
> already target-specific?
> (If not, should this be added to the docs?)

Checking the arch/ABI value is important so that you can ensure that
you are using the syscall number in the proper context.  For example,
look at the access(2) syscall: it is undefined on some ABIs and can
take either a value of 20, 21, or 33 depending on the arch/ABI.
Unfortunately this is rather common.

Checking the arch/ABI value is also handy if you want to quickly
disallow certain ABIs on a system that supports multiple ABI, e.g.
disabling 32-bit x86 on a 64-bit x86_64 system.

> Would it make sense to expose the audit arch matching the syscall numbers in
> the uapi headers?

Yes, which is why the existing headers do so ;)  If you don't see the
header files I mentioned above, it may be worth checking your kernel
source repository and your distribution's installed kernel header
files.

-- 
paul moore
www.paul-moore.com

  reply	other threads:[~2021-06-28 17:00 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-28  7:31 Thomas Weißschuh
2021-06-28 16:59 ` Paul Moore [this message]
2021-06-28 17:13   ` Thomas Weißschuh
2021-06-28 17:34     ` Paul Moore
2021-06-28 17:58       ` Thomas Weißschuh
2021-06-28 22:43         ` Paul Moore
2021-06-29 10:40           ` Thomas Weißschuh
2021-06-29 23:41             ` Paul Moore

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