Received-SPF: pass (google.com: domain of linux-kernel+bounces-207754-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45d1:ec00::1 as permitted sender) client-ip=2604:1380:45d1:ec00::1;
Message-ID: <d827e5ab-6204-4a47-a8af-a1eedd76b070@suse.com>
Date: Mon, 10 Jun 2024 10:08:18 +0300
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH] x86/boot: add prototype for __fortify_panic()
From: Nikolay Borisov <nik.borisov@suse.com>
To: Kees Cook <kees@kernel.org>, Jeff Johnson <quic_jjohnson@quicinc.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
 Borislav Petkov <bp@alien8.de>, Dave Hansen <dave.hansen@linux.intel.com>,
 x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
 linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org,
 kernel-janitors@vger.kernel.org
References: <20240529-fortify_panic-v1-1-9923d5c77657@quicinc.com>
 <0d3f7c58-7fc0-4e8b-b6fb-c4d0d9969ce7@suse.com>
 <e42c4984-d4a2-45b1-b93d-7471000766b7@quicinc.com>
 <202405310923.78257B2B3@keescook>
 <a54db95c-e22a-4e13-ae4b-6a5a67d1c49b@suse.com>
Content-Language: en-US
In-Reply-To: <a54db95c-e22a-4e13-ae4b-6a5a67d1c49b@suse.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit


On 1.06.24 г. 10:27 ч., Nikolay Borisov wrote:
> 
> 
> On 31.05.24 г. 19:28 ч., Kees Cook wrote:
>> On Thu, May 30, 2024 at 09:23:36AM -0700, Jeff Johnson wrote:
>>> On 5/30/2024 8:42 AM, Nikolay Borisov wrote:
>>>>
>>>>
>>>> On 29.05.24 г. 21:09 ч., Jeff Johnson wrote:
>>>>> As discussed in [1] add a prototype for __fortify_panic() to fix the
>>>>> 'make W=1 C=1' warning:
>>>>>
>>>>> arch/x86/boot/compressed/misc.c:535:6: warning: symbol 
>>>>> '__fortify_panic' was not declared. Should it be static?
>>>>
>>>> Actually doesn't it make sense to have this defined under ../string.h ?
>>>> Actually given that we don't have any string fortification under the
>>>> boot/  why have the fortify _* functions at all ?
>>>
>>> I'll let Kees answer these questions since I just took guidance from 
>>> him :)
>>
>> Ah-ha, I see what's happening. When not built with
>> CONFIG_FORTIFY_SOURCE, fortify-string.h isn't included. But since misc.c
>> has the function definition, we get a warning that the function
>> declaration was never seen. This is likely the better solution:
> 
> fortify-strings.h is used in include/linux/string.h. However all the 
> files in the decompressor are using a local copy of string.h and not the 
> kernel-wide. When pre-processing misc.c with FORTIFY_SOURCE enabled 
> here's the status:
> 
> $ grep -i fortify  arch/x86/boot/compressed/misc.i
> void __fortify_panic(const u8 reason, size_t avail, size_t size)
> 
> It seems the decompressor is not using fortify-string at all because 
> it's not using the global string.h ?

Kees, care to comment about my observation? Have I missed anything? 
Reading the following articles : 
https://www.redhat.com/en/blog/enhance-application-security-fortifysource

it seems that fortification comes from using the system header string.h 
(in our case that'd be include/linux/string.h) which is not being used 
by the decompressor at all so simply removing the function definition 
should be the correct fix, no ?


<snip>