This is a note to let you know that I've just added the patch titled

x86/microcode/AMD: Do not load when running on a hypervisor

to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: x86-microcode-amd-do-not-load-when-running-on-a-hypervisor.patch and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From a15a753539eca8ba243d576f02e7ca9c4b7d7042 Mon Sep 17 00:00:00 2001

From: Borislav Petkov bp@suse.de Date: Sun, 18 Dec 2016 17:44:13 +0100 Subject: x86/microcode/AMD: Do not load when running on a hypervisor

From: Borislav Petkov bp@suse.de

commit a15a753539eca8ba243d576f02e7ca9c4b7d7042 upstream.

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@suse.de Tested-by: Juergen Gross jgross@suse.com Tested-by: Boris Ostrovsky boris.ostrovsky@oracle.com Acked-by: Juergen Gross jgross@suse.com Link: http://lkml.kernel.org/r/20161218164414.9649-4-bp@alien8.de Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: Rolf Neugebauer rolf.neugebauer@docker.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- arch/x86/kernel/cpu/microcode/core.c | 28 +++++++++++++++++++--------- 1 file changed, 19 insertions(+), 9 deletions(-)

--- a/arch/x86/kernel/cpu/microcode/core.c +++ b/arch/x86/kernel/cpu/microcode/core.c @@ -43,7 +43,7 @@ #define MICROCODE_VERSION "2.01"

static struct microcode_ops *microcode_ops; -static bool dis_ucode_ldr; +static bool dis_ucode_ldr = true;

/* * Synchronization. @@ -73,6 +73,7 @@ struct cpu_info_ctx { static bool __init check_loader_disabled_bsp(void) { static const char *__dis_opt_str = "dis_ucode_ldr"; + u32 a, b, c, d;

#ifdef CONFIG_X86_32 const char *cmdline = (const char *)__pa_nodebug(boot_command_line); @@ -85,8 +86,23 @@ static bool __init check_loader_disabled 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; } @@ -118,9 +134,6 @@ void __init load_ucode_bsp(void) if (check_loader_disabled_bsp()) return;

- if (!have_cpuid_p()) - return; - vendor = x86_cpuid_vendor(); family = x86_cpuid_family();

@@ -154,9 +167,6 @@ void load_ucode_ap(void) if (check_loader_disabled_ap()) return;

- if (!have_cpuid_p()) - return; - vendor = x86_cpuid_vendor(); family = x86_cpuid_family();

Patches currently in stable-queue which might be from bp@suse.de are

queue-4.9/x86-microcode-amd-do-not-load-when-running-on-a-hypervisor.patch