linux-kernel - Re: [PATCH] x86/mm/mem_encrypt: Disable all instrumentation for SME early boot code

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Message-ID: <1beb4b7b-a4c1-0f60-3aa8-640754e30137@amd.com>
Date:   Mon, 29 Apr 2019 20:16:07 +0000
From:   Gary R Hook <ghook@....com>
To:     Borislav Petkov <bp@...en8.de>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        "Hook, Gary" <Gary.Hook@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "luto@...nel.org" <luto@...nel.org>,
        Alexander Potapenko <glider@...gle.com>
Subject: Re: [PATCH] x86/mm/mem_encrypt: Disable all instrumentation for SME
 early boot code

On 4/26/19 11:24 AM, Borislav Petkov wrote:
> On Fri, Apr 26, 2019 at 03:11:17PM +0000, Gary R Hook wrote:
>> 2) Turn off instrumentation for lib/cmdline.c. The risk is that any
>>      changes to its code would not enjoy the benefits of KASAN/etc testing
>>      (if enabled).
> 
> What happened to Thomas' suggestion to turn off instrumentation for
> those files only when CONFIG_AMD_MEM_ENCRYPT=y?
> 
> Which is a variant of 2) above with ifdeffery.
> 

Ah, very good. That one escaped my list.

Yes, option 4 would be a combination of using a local copy of strncmp() 
and disabling instrumentation (KASAN, KCOV, whatever) for 
arch/x86/lib/cmdline.c when SME is enabled.

I have any/all of these ready to repost as a version 2 offering. What 
say you?

grh