AUDIT_ARCH_ and __NR_syscall constants for seccomp filters

From: "Thomas Weißschuh" <linux@weissschuh.net>
To: linux-audit@redhat.com, bpf@vger.kernel.org
Subject: AUDIT_ARCH_ and __NR_syscall constants for seccomp filters
Date: Mon, 28 Jun 2021 09:31:53 +0200	[thread overview]
Message-ID: <0b926f59-464d-4b67-8f32-329cf9695cf7@t-8ch.de> (raw)

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.

Background:

I am writing a seccomp BPF filter using the syscall constants to get the
correct syscall numbers for the target architecture.

seccomp_filter.rst tells users to always check the arch values.
But there does not seem a way to get the correct AUDIT_ARCH_ value from the
kernel headers.

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?)

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

Link to the actual BPF code:
https://github.com/t-8ch/qmk_firmware/blob/optimize-udev/util/udev/qmk_id.c#L154

Thanks,
Thomas