From 0fdb006a5af7f391a6de4ce810aba4af46c427e4 Mon Sep 17 00:00:00 2001

From: Andy Lutomirski <luto@amacapital.net>

Date: Fri, 5 Dec 2014 19:03:28 -0800

Subject: [PATCH] x86, kvm: Clear paravirt_enabled on KVM guests for espfix32's

 benefit

paravirt_enabled has the following effects:

 - Disables the F00F bug workaround warning.  There is no F00F bug

   workaround any more because Linux's standard IDT handling already

   works around the F00F bug, but the warning still exists.  This

   is only cosmetic, and, in any event, there is no such thing as

   KVM on a CPU with the F00F bug.

 - Disables 32-bit APM BIOS detection.  On a KVM paravirt system,

   there should be no APM BIOS anyway.

 - Disables tboot.  I think that the tboot code should check the

   CPUID hypervisor bit directly if it matters.

 - paravirt_enabled disables espfix32.  espfix32 should *not* be

   disabled under KVM paravirt.

The last point is the purpose of this patch.  It fixes a leak of the

high 16 bits of the kernel stack address on 32-bit KVM paravirt

guests.

While I'm at it, this removes pv_info setup from kvmclock.  That

code seems to serve no purpose.

Cc: stable@vger.kernel.org

Signed-off-by: Andy Lutomirski <luto@amacapital.net>

---

 arch/x86/kernel/kvm.c      | 9 ++++++++-

 arch/x86/kernel/kvmclock.c | 2 --

 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c

index 3dd8e2c4d74a..07de51f66deb 100644

--- a/arch/x86/kernel/kvm.c

+++ b/arch/x86/kernel/kvm.c

@@ -282,7 +282,14 @@ NOKPROBE_SYMBOL(do_async_page_fault);

 static void __init paravirt_ops_setup(void)

 {

 	pv_info.name = "KVM";

-	pv_info.paravirt_enabled = 1;

+

+	/*

+	 * KVM isn't paravirt in the sense of paravirt_enabled.  A KVM

+	 * guest kernel works like a bare metal kernel with additional

+	 * features, and paravirt_enabled is about features that are

+	 * missing.

+	 */

+	pv_info.paravirt_enabled = 0;

 	if (kvm_para_has_feature(KVM_FEATURE_NOP_IO_DELAY))

 		pv_cpu_ops.io_delay = kvm_io_delay;

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c

index d9156ceecdff..d4d9a8ad7893 100644

--- a/arch/x86/kernel/kvmclock.c

+++ b/arch/x86/kernel/kvmclock.c

@@ -263,8 +263,6 @@ void __init kvmclock_init(void)

 #endif

 	kvm_get_preset_lpj();

 	clocksource_register_hz(&kvm_clock, NSEC_PER_SEC);

-	pv_info.paravirt_enabled = 1;

-	pv_info.name = "KVM";

 	if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE_STABLE_BIT))

 		pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT);

-- 

2.1.0