linux-hardening - Re: [REGRESSION] 5.16rc1: SA

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Message-ID: <202111171728.D85A4E2571@keescook>
Date:   Wed, 17 Nov 2021 17:32:20 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Kyle Huey <me@...ehuey.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andrea Righi <andrea.righi@...onical.com>,
        Shuah Khan <shuah@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        linux-hardening@...r.kernel.org,
        Robert O'Callahan <rocallahan@...il.com>
Subject: Re: [REGRESSION] 5.16rc1: SA_IMMUTABLE breaks debuggers

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