Re: [PATCH] x86, CPU, AMD: Add workaround for family 16h, erratum 793

Pavel Machek
2014-01-17T22:28:24Z

On Tue 2014-01-14 17:27:23, Borislav Petkov wrote:
> From: Borislav Petkov <bp@suse.de>
>
> This adds the workaround for erratum 793 as a precaution in case not
> every BIOS implements it. This addresses CVE-2013-6885.
>
> Signed-off-by: Borislav Petkov <bp@suse.de>
> ---
> arch/x86/kernel/cpu/amd.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index 4a48e8bbd857..e4d6f8c91f51 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -507,6 +507,17 @@ static void early_init_amd(struct cpuinfo_x86 *c)
> set_cpu_cap(c, X86_FEATURE_EXTD_APICID);
> }
> #endif
> +
> +#define MSR_AMD_LS_CFG 0xc0011020
> + /* F16h, models 00h-0fh, erratum 793 */
> + if (c->x86 == 0x16 && c->x86_model <= 0xf) {
> + u64 val;
> +
> + rdmsrl(MSR_AMD_LS_CFG, val);
> + if (!(val & BIT(15)))
> + wrmsrl(MSR_AMD_LS_CFG, val | BIT(15));

Would it make sense to printk() a warning?

BIOS is clearly buggy in this case, and it may cause problems with
another operating system, earlier kernel, or maybe early in boot
before MSR is written...
Pavel
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