Received-SPF: pass (google.com: domain of linux-kernel+bounces-197752-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.48.161 as permitted sender) client-ip=147.75.48.161;
Message-ID: <a54db95c-e22a-4e13-ae4b-6a5a67d1c49b@suse.com>
Date: Sat, 1 Jun 2024 10:27:28 +0300
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH] x86/boot: add prototype for __fortify_panic()
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>
Content-Language: en-US
From: Nikolay Borisov <nik.borisov@suse.com>
In-Reply-To: <202405310923.78257B2B3@keescook>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit


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 ?


> 
> 
> diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
> index b70e4a21c15f..3f21a5e218f8 100644
> --- a/arch/x86/boot/compressed/misc.c
> +++ b/arch/x86/boot/compressed/misc.c
> @@ -532,7 +532,9 @@ asmlinkage __visible void *extract_kernel(void *rmode, unsigned char *output)
>   	return output + entry_offset;
>   }
>   
> +#ifdef CONFIG_FORTIFY_SOURCE
>   void __fortify_panic(const u8 reason, size_t avail, size_t size)
>   {
>   	error("detected buffer overflow");
>   }
> +#endif
> 
> 
> Jeff, can you test this? (I still haven't been able to reproduce the
> warning.)
>