linux-kernel - Re: [PATCH 12/27] x86/msr: Restrict MSR access when the kernel is locked down

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Date:   Sat, 21 Oct 2017 12:39:19 +0800
From:   joeyli <jlee@...e.com>
To:     David Howells <dhowells@...hat.com>
Cc:     Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        linux-security-module@...r.kernel.org, linux-efi@...r.kernel.org,
        matthew.garrett@...ula.com, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, jforbes@...hat.com
Subject: Re: [PATCH 12/27] x86/msr: Restrict MSR access when the kernel is
 locked down

On Fri, Oct 20, 2017 at 09:48:16PM +0100, David Howells wrote:
> Alan Cox <gnomes@...rguk.ukuu.org.uk> wrote:
> 
> > There are a load of standard tools that use this so I think you are going
> > to need a whitelist. Can you at least log *which* MSR in the failing case
> > so a whitelist can be built over time ?
> 
[...snip]
> 
> And do you know where wrmsr_safe_regs() might be found?  I can see things
> using it and exporting it, but no implementation, so I'm guessing it's
> macroised somewhere.

Looks the definition is in 

arch/x86/lib/msr-reg.S

#ifdef CONFIG_X86_64
/*
 * int {rdmsr,wrmsr}_safe_regs(u32 gprs[8]);
 *
 * reg layout: u32 gprs[eax, ecx, edx, ebx, esp, ebp, esi, edi]
 *
 */
.macro op_safe_regs op
ENTRY(\op\()_safe_regs)
        pushq %rbx
        pushq %r12
...

Regards
Joey Lee