Re: [PATCH v8 1/3] seccomp: let the tracer skip a syscall independently of its number

[sashiko-bot@kernel.org]

> From: Davide Berardi <berardi.dav@gmail.com>
> 
> At a PTRACE_EVENT_SECCOMP stop the tracer can only skip the system call
> by setting its number to -1, which seccomp reads back with
> syscall_get_nr().  This depends on how each architecture lays out the
> syscall number and the return value in the registers:
> 
>  - on some architectures the syscall number shares a register with the
>    return value (e.g. v0 on MIPS), so setting the return value after the
>    number would overwrite the skip request, and each of them needs its
>    own way to keep it (MIPS keeps a copy of the number in thread_info);
> 
>  - on s390 syscall_get_nr() returns the low 16 bits of int_code, so -1
>    is read back as 65535: seccomp does not skip the call but runs the
>    filters again on syscall 65535, which kills the task if the filter
> [ ... ]
> The next patch uses this in PTRACE_SET_SYSCALL_INFO.
> 
> Suggested-by: Michal Suchánek <msuchanek@suse.de>
> Assisted-by: claude-opus-5-5
> Signed-off-by: Renzo Davoli <renzo@cs.unibo.it>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261020065635.490528-1-renzo@cs.unibo.it?part=1