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Date:   Wed, 17 Nov 2021 17:32:20 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Kyle Huey <me@kylehuey.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Andrea Righi <andrea.righi@canonical.com>,
        Shuah Khan <shuah@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
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        "open list:KERNEL SELFTEST FRAMEWORK" 
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        open list <linux-kernel@vger.kernel.org>,
        linux-hardening@vger.kernel.org,
        Robert O'Callahan <rocallahan@gmail.com>
Subject: Re: [REGRESSION] 5.16rc1: SA_IMMUTABLE breaks debuggers
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On Wed, Nov 17, 2021 at 05:20:33PM -0800, Kyle Huey wrote:
> Yeah that's one way to solve the problem. I think you're right that
> fundamentally the problem here is that what SECCOMP_RET_KILL wants is
> not really a signal. To the extent that it wants a signal, what it
> really wants is SIGKILL, and the problem here is the code trying to
> act like SIGKILL but call it SIGSYS. I assume the ship for fixing that
> sailed years ago though.

Yeah, this was IIRC, a specific design choice (to distinguish a seccomp
KILL from a SIGKILL), as desired by the sandboxing folks, and instead
of using two different signals (one for KILL and one for TRAP), both
used SIGSYS, with the KILL variant being uncatchable.

-- 
Kees Cook