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

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Message-ID: <3bfae142-7d38-99c5-a086-5d2e79ec586d@amd.com>
Date:   Mon, 29 Apr 2019 21:22:48 +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 4/29/19 3:51 PM, Borislav Petkov wrote:
> [CAUTION: External Email]
> 
> On Mon, Apr 29, 2019 at 08:16:07PM +0000, Gary R Hook wrote:
>> Yes, option 4 would be a combination of using a local copy of strncmp()
> 
> Why the local copy?

Seemed suitable, since it's tiny. But I'm not married to the idea.

> 
>> and disabling instrumentation (KASAN, KCOV, whatever) for
>> arch/x86/lib/cmdline.c when SME is enabled.
> 
> I think this should suffice. You only disable instrumentation when
> CONFIG_AMD_MEM_ENCRYPT=y and not do any local copies but use the generic
> functions.

Okay, super.  I'll post a v2 that does that.

Do we want to document the subordinate functions in their respective 
source files so that a future editor would (hopefully) be made aware of 
this use?

grh