Commit d566b670 authored by Ben Hutchings's avatar Ben Hutchings

[x86] microcode: Do not load when running on a hypervisor

Closes: #898067, regression in 3.16.56-1
parent 01fef01c
......@@ -5,6 +5,8 @@ linux (3.16.56-1+deb8u1) UNRELEASED; urgency=high
* tun: allow positive return values on dev_get_valid_name() call
(Closes: #897427, regression in 3.16.56-1)
* [x86] microcode: Fix accessing dis_ucode_ldr on 32-bit
* [x86] microcode: Do not load when running on a hypervisor
(Closes: #898067, regression in 3.16.56-1)
-- Ben Hutchings <ben@decadent.org.uk> Mon, 30 Apr 2018 20:25:34 +0100
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
Origin: https://git.kernel.org/linus/a15a753539eca8ba243d576f02e7ca9c4b7d7042
Bug-Debian: https://bugs.debian.org/898067
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>
[bwh: Backported to 3.16:
- Early microcode loader is optional, so only set dis_ucode_ldr by default
if it is enabled
- Adjust context, filename]
---
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -97,7 +97,7 @@ MODULE_LICENSE("GPL");
static struct microcode_ops *microcode_ops;
-bool dis_ucode_ldr;
+bool dis_ucode_ldr = IS_ENABLED(CONFIG_MICROCODE_EARLY);
module_param(dis_ucode_ldr, bool, 0);
/*
--- a/arch/x86/kernel/cpu/microcode/core_early.c
+++ b/arch/x86/kernel/cpu/microcode/core_early.c
@@ -76,6 +76,8 @@ static int x86_family(void)
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";
@@ -88,8 +90,23 @@ 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;
}
@@ -101,9 +118,6 @@ void __init load_ucode_bsp(void)
if (check_loader_disabled_bsp())
return;
- if (!have_cpuid_p())
- return;
-
vendor = x86_vendor();
x86 = x86_family();
@@ -137,9 +151,6 @@ void load_ucode_ap(void)
if (check_loader_disabled_ap())
return;
- if (!have_cpuid_p())
- return;
-
vendor = x86_vendor();
x86 = x86_family();
......@@ -98,6 +98,7 @@ bugfix/x86/kvm-x86-bit-ops-emulation-ignores-offset-on-64-bit.patch
bugfix/x86/KVM-x86-pass-host_initiated-to-functions-that-read-M.patch
bugfix/x86/KVM-VMX-Fix-host-initiated-access-to-guest-MSR_TSC_A.patch
bugfix/x86/x86-microcode-fix-accessing-dis_ucode_ldr-on-32-bit.patch
bugfix/x86/x86-microcode-amd-do-not-load-when-running-on-a-hype.patch
features/all/readq-writeq-Add-explicit-lo_hi_-read-write-_q-and-h.patch
......
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