Re: [tip:x86/boot] x86/mm: Enable KASLR for physical mapping memory regions

[Kees Cook <keescook@xxxxxxxxxxxx>]

On Tue, Aug 16, 2016 at 10:50 AM, Borislav Petkov <bp@xxxxxxxxx> wrote:
> On Tue, Aug 16, 2016 at 05:54:12PM +0200, Borislav Petkov wrote:
>> Ok, I ran this in a guest and it finds the microcode patches properly.
>
> Here's a better version to take care of the APs too:
>
> ---
> diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
> index 27a0228c9cae..05242322e324 100644
> --- a/arch/x86/kernel/cpu/microcode/amd.c
> +++ b/arch/x86/kernel/cpu/microcode/amd.c
> @@ -355,6 +355,7 @@ void load_ucode_amd_ap(void)
>         unsigned int cpu = smp_processor_id();
>         struct equiv_cpu_entry *eq;
>         struct microcode_amd *mc;
> +       u8 *cont;
>         u32 rev, eax;
>         u16 eq_id;
>
> @@ -371,8 +372,12 @@ void load_ucode_amd_ap(void)
>         if (check_current_patch_level(&rev, false))
>                 return;
>
> +#ifdef CONFIG_RANDOMIZE_MEMORY
> +       cont = container + PAGE_OFFSET - __PAGE_OFFSET_BASE;
> +#endif
> +
>         eax = cpuid_eax(0x00000001);
> -       eq  = (struct equiv_cpu_entry *)(container + CONTAINER_HDR_SZ);
> +       eq  = (struct equiv_cpu_entry *)(cont + CONTAINER_HDR_SZ);

Am I misreading this? Shouldn't it be:

       cont = container;
#ifdef CONFIG_RANDOMIZE_MEMORY
       cont += PAGE_OFFSET - __PAGE_OFFSET_BASE;
#endif

(otherwise cont is undefined in the RANDOMIZE_MEMORY=n case?)

>
>         eq_id = find_equiv_id(eq, eax);
>         if (!eq_id)
> @@ -434,6 +439,10 @@ int __init save_microcode_in_initrd_amd(void)
>         else
>                 container = cont_va;
>
> +#ifdef CONFIG_RANDOMIZE_MEMORY
> +       container += PAGE_OFFSET - __PAGE_OFFSET_BASE;
> +#endif
> +
>         eax   = cpuid_eax(0x00000001);
>         eax   = ((eax >> 8) & 0xf) + ((eax >> 20) & 0xff);
>
>
> --
> Regards/Gruss,
>     Boris.
>
> ECO tip #101: Trim your mails when you reply.
> --


-Kees

-- 
Kees Cook
Nexus Security
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