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    SubjectRe: [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@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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