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Date: Mon, 4 Mar 2024 09:40:01 -0800
From: Kees Cook <keescook@chromium.org>
To: Jann Horn <jannh@google.com>
Cc: Jiangfeng Xiao <xiaojiangfeng@huawei.com>, gustavoars@kernel.org,
	akpm@linux-foundation.org, jpoimboe@kernel.org,
	peterz@infradead.org, dave.hansen@linux.intel.com,
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	linux-hardening@vger.kernel.org, linux-mm@kvack.org,
	nixiaoming@huawei.com, kepler.chenxin@huawei.com,
	wangbing6@huawei.com, wangfangpeng1@huawei.com,
	douzhaolei@huawei.com
Subject: Re: [PATCH] usercopy: delete __noreturn from usercopy_abort
Message-ID: <202403040938.D770633@keescook>
References: <1709516385-7778-1-git-send-email-xiaojiangfeng@huawei.com>
 <CAG48ez1h9X7Qv-5OR6hAhwnSOng6_PSXBaR6cT7xrk2Wzu39Yg@mail.gmail.com>
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On Mon, Mar 04, 2024 at 04:15:07PM +0100, Jann Horn wrote:
> On Mon, Mar 4, 2024 at 3:02 AM Jiangfeng Xiao <xiaojiangfeng@huawei.com> wrote:
> > When the last instruction of a noreturn function is a call
> > to another function, the return address falls outside
> > of the function boundary. This seems to cause kernel
> > to interrupt the backtrace.

FWIW, all email from huawei.com continues to get eaten by anti-spam
checking. I've reported this a few times -- it'd be really nice if the
domain configuration could get fixed.

> [...]
> > Delete __noreturn from usercopy_abort,
> 
> This sounds like the actual bug is in the backtracing logic? I don't
> think removing __noreturn annotations from an individual function is a
> good fix, since the same thing can happen with other __noreturn
> functions depending on what choices the compiler makes.

Yeah, NAK. usercopy_abort() doesn't return. It ends with BUG().

-- 
Kees Cook