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

[joeyli]

On Fri, Oct 20, 2017 at 09:48:16PM +0100, David Howells wrote:
> Alan Cox <gnomes at lxorguk.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
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