linux-hardening - Re: [PATCH] usercopy: delete __noreturn from usercopy

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Date: Tue, 5 Mar 2024 11:31:06 +0800
From: Jiangfeng Xiao <xiaojiangfeng@...wei.com>
To: Kees Cook <keescook@...omium.org>, Jann Horn <jannh@...gle.com>
CC: <gustavoars@...nel.org>, <akpm@...ux-foundation.org>,
	<jpoimboe@...nel.org>, <peterz@...radead.org>, <dave.hansen@...ux.intel.com>,
	<kirill.shutemov@...ux.intel.com>, <linux-kernel@...r.kernel.org>,
	<linux-hardening@...r.kernel.org>, <linux-mm@...ck.org>,
	<nixiaoming@...wei.com>, <kepler.chenxin@...wei.com>, <wangbing6@...wei.com>,
	<wangfangpeng1@...wei.com>, <douzhaolei@...wei.com>
Subject: Re: [PATCH] usercopy: delete __noreturn from usercopy_abort



On 2024/3/5 1:40, Kees Cook wrote:
> 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@...wei.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().
> 
When the user directly or indirectly calls usercopy_abort,
the final call stack is incorrect, and the
code where the problem occurs cannot be located.
In this case, the user will be frustrated.

For the usercopy_abort function, whether '__noreturn' is added
does not affect the internal behavior of the usercopy_abort function.
Therefore, it is recommended that '__noreturn' be deleted
so that backtrace can work properly.