From 9de6fe3c28d6d8feadfad907961f1f31b85c6985 Mon Sep 17 00:00:00 2001
From: Xiaoyao Li <xiaoyao.li@intel.com>
Date: Fri, 10 Apr 2020 13:54:01 +0200
Subject: [PATCH] KVM: x86: Emulate split-lock access as a write in emulator
Git-commit: 9de6fe3c28d6d8feadfad907961f1f31b85c6985
Patch-mainline: v5.7-rc1
References: bsc#1187959
Emulate split-lock accesses as writes if split lock detection is on
to avoid #AC during emulation, which will result in a panic(). This
should never occur for a well-behaved guest, but a malicious guest can
manipulate the TLB to trigger emulation of a locked instruction[1].
More discussion can be found at [2][3].
[1] https://lkml.kernel.org/r/8c5b11c9-58df-38e7-a514-dc12d687b198@redhat.com
[2] https://lkml.kernel.org/r/20200131200134.GD18946@linux.intel.com
[3] https://lkml.kernel.org/r/20200227001117.GX9940@linux.intel.com
Suggested-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://lkml.kernel.org/r/20200410115517.084300242@linutronix.de
Acked-by: Dario Faggioli <dfaggioli@suse.com>
---
arch/x86/kvm/x86.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5747,6 +5747,7 @@ static int emulator_cmpxchg_emulated(str
{
struct kvm_host_map map;
struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
+ u64 page_line_mask;
gpa_t gpa;
char *kaddr;
bool exchanged;
@@ -5761,7 +5762,16 @@ static int emulator_cmpxchg_emulated(str
(gpa & PAGE_MASK) == APIC_DEFAULT_PHYS_BASE)
goto emul_write;
- if (((gpa + bytes - 1) & PAGE_MASK) != (gpa & PAGE_MASK))
+ /*
+ * Emulate the atomic as a straight write to avoid #AC if SLD is
+ * enabled in the host and the access splits a cache line.
+ */
+ if (boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT))
+ page_line_mask = ~(cache_line_size() - 1);
+ else
+ page_line_mask = PAGE_MASK;
+
+ if (((gpa + bytes - 1) & page_line_mask) != (gpa & page_line_mask))
goto emul_write;
if (kvm_vcpu_map(vcpu, gpa_to_gfn(gpa), &map))