linux-kernel - Re: [musl] AT_MINSIGSTKSZ mismatched interpretation kernel vs libc

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Message-ID: <87v7zetg1j.fsf@oldenburg3.str.redhat.com>
Date: Mon, 02 Sep 2024 14:07:36 +0200
From: Florian Weimer <fweimer@...hat.com>
To: Rich Felker <dalias@...c.org>
Cc: "H.J. Lu" <hjl.tools@...il.com>,  Linux Kernel Mailing List
 <linux-kernel@...r.kernel.org>,  linux-api@...r.kernel.org,
  libc-alpha@...rceware.org,  musl@...ts.openwall.com
Subject: Re: [musl] AT_MINSIGSTKSZ mismatched interpretation kernel vs libc

* Rich Felker:

> This is ambiguously worded (does "operating system" mean kernel?) and
> does not agree with POSIX, which defines it as:
>
>     Minimum stack size for a signal handler.
>
> And otherwise just specifies that sigaltstack shall fail if given a
> smaller size.
>
> The POSIX definition is also underspecified but it's clear that it
> should be possible to execute at least a do-nothing signal handler
> (like one which immediately returns and whose sole purpose is to
> induce EINTR when intalled without SA_RESTART), or even a minimal one
> that does something like storing to a global variable, with such a
> small stack. Allowing a size where even a do-nothing signal handler
> results in a memory-clobbering overflow or access fault seems
> non-conforming to me.

POSIX does not specify what happens on a stack overflow (or more
generally, if most resource limits are exceeded), so I think the
behavior is conforming on a technicality.

Thanks,
Florian