ACK: [Xenial][PATCH 1/1] x86/microcode/AMD: Do not load when running on a hypervisor

[Stefan Bader]

On 28.03.2018 18:28, Kamal Mostafa wrote:
> From: Borislav Petkov <bp at suse.de>
> 
> BugLink: http://bugs.launchpad.net/bugs/1758869
> 
> commit a15a753539eca8ba243d576f02e7ca9c4b7d7042 upstream with minor
> adjustments.
> 
> Doing so is completely void of sense for multiple reasons so prevent
> it. Set dis_ucode_ldr to true and thus disable the microcode loader by
> default to address xen pv guests which execute the AP path but not the
> BSP path.
> 
> By having it turned off by default, the APs won't run into the loader
> either.
> 
> Also, check CPUID(1).ECX[31] which hypervisors set. Well almost, not the
> xen pv one. That one gets the aforementioned "fix".
> 
> Also, improve the detection method by caching the final decision whether
> to continue loading in dis_ucode_ldr and do it once on the BSP. The APs
> then simply test that value.
> 
> Signed-off-by: Borislav Petkov <bp at suse.de>
> Tested-by: Juergen Gross <jgross at suse.com>
> Tested-by: Boris Ostrovsky <boris.ostrovsky at oracle.com>
> Acked-by: Juergen Gross <jgross at suse.com>
> Link: http://lkml.kernel.org/r/20161218164414.9649-4-bp@alien8.de
> Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
> Cc: <stable at vger.kernel.org> # 4.4.x
> Signed-off-by: Rolf Neugebauer <rolf.neugebauer at docker.com>
> (back-ported from commit a15a753539eca8ba243d576f02e7ca9c4b7d7042)
> Reference: https://lkml.org/lkml/2018/2/8/455
> Signed-off-by: Kamal Mostafa <kamal at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>

> ---
>  arch/x86/kernel/cpu/microcode/core.c | 28 +++++++++++++++++++---------
>  1 file changed, 19 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
> index 57ea794..d52b5e0 100644
> --- a/arch/x86/kernel/cpu/microcode/core.c
> +++ b/arch/x86/kernel/cpu/microcode/core.c
> @@ -44,7 +44,7 @@
>  
>  static struct microcode_ops	*microcode_ops;
>  
> -static bool dis_ucode_ldr;
> +static bool dis_ucode_ldr = true;
>  
>  static int __init disable_loader(char *str)
>  {
> @@ -81,6 +81,7 @@ struct cpu_info_ctx {
>  
>  static bool __init check_loader_disabled_bsp(void)
>  {
> +	u32 a, b, c, d;
>  #ifdef CONFIG_X86_32
>  	const char *cmdline = (const char *)__pa_nodebug(boot_command_line);
>  	const char *opt	    = "dis_ucode_ldr";
> @@ -93,8 +94,23 @@ static bool __init check_loader_disabled_bsp(void)
>  	bool *res = &dis_ucode_ldr;
>  #endif
>  
> -	if (cmdline_find_option_bool(cmdline, option))
> -		*res = true;
> +	if (!have_cpuid_p())
> +		return *res;
> +
> +	a = 1;
> +	c = 0;
> +	native_cpuid(&a, &b, &c, &d);
> +
> +	/*
> +	 * CPUID(1).ECX[31]: reserved for hypervisor use. This is still not
> +	 * completely accurate as xen pv guests don't see that CPUID bit set but
> +	 * that's good enough as they don't land on the BSP path anyway.
> +	 */
> +	if (c & BIT(31))
> +		return *res;
> +
> +	if (cmdline_find_option_bool(cmdline, option) <= 0)
> +		*res = false;
>  
>  	return *res;
>  }
> @@ -126,9 +142,6 @@ void __init load_ucode_bsp(void)
>  	if (check_loader_disabled_bsp())
>  		return;
>  
> -	if (!have_cpuid_p())
> -		return;
> -
>  	vendor = x86_vendor();
>  	family = x86_family();
>  
> @@ -162,9 +175,6 @@ void load_ucode_ap(void)
>  	if (check_loader_disabled_ap())
>  		return;
>  
> -	if (!have_cpuid_p())
> -		return;
> -
>  	vendor = x86_vendor();
>  	family = x86_family();
>  
> 


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