[PATCH v2 10/13] KVM: x86: Protect memory accesses from Spectre-v1/L1TF attacks in x86.c

[Marios Pomonis <pomonis@google.com>]

This fixes Spectre-v1/L1TF vulnerabilities in
vmx_read_guest_seg_selector(), vmx_read_guest_seg_base(),
vmx_read_guest_seg_limit() and vmx_read_guest_seg_ar().
These functions contain index computations based on the
(attacker-influenced) segment value.

Fixes: commit 2fb92db1ec08 ("KVM: VMX: Cache vmcs segment fields")

Signed-off-by: Nick Finco <nifi@google.com>
Signed-off-by: Marios Pomonis <pomonis@google.com>
Reviewed-by: Andrew Honig <ahonig@google.com>
Cc: stable@vger.kernel.org
---
 arch/x86/kvm/vmx/vmx.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index d39475e2d44e..82b25f1812aa 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -753,7 +753,9 @@ static bool vmx_segment_cache_test_set(struct vcpu_vmx *vmx, unsigned seg,
 
 static u16 vmx_read_guest_seg_selector(struct vcpu_vmx *vmx, unsigned seg)
 {
-	u16 *p = &vmx->segment_cache.seg[seg].selector;
+	size_t size = ARRAY_SIZE(vmx->segment_cache.seg);
+	size_t index = array_index_nospec(seg, size);
+	u16 *p = &vmx->segment_cache.seg[index].selector;
 
 	if (!vmx_segment_cache_test_set(vmx, seg, SEG_FIELD_SEL))
 		*p = vmcs_read16(kvm_vmx_segment_fields[seg].selector);
@@ -762,7 +764,9 @@ static u16 vmx_read_guest_seg_selector(struct vcpu_vmx *vmx, unsigned seg)
 
 static ulong vmx_read_guest_seg_base(struct vcpu_vmx *vmx, unsigned seg)
 {
-	ulong *p = &vmx->segment_cache.seg[seg].base;
+	size_t size = ARRAY_SIZE(vmx->segment_cache.seg);
+	size_t index = array_index_nospec(seg, size);
+	ulong *p = &vmx->segment_cache.seg[index].base;
 
 	if (!vmx_segment_cache_test_set(vmx, seg, SEG_FIELD_BASE))
 		*p = vmcs_readl(kvm_vmx_segment_fields[seg].base);
@@ -771,7 +775,9 @@ static ulong vmx_read_guest_seg_base(struct vcpu_vmx *vmx, unsigned seg)
 
 static u32 vmx_read_guest_seg_limit(struct vcpu_vmx *vmx, unsigned seg)
 {
-	u32 *p = &vmx->segment_cache.seg[seg].limit;
+	size_t size = ARRAY_SIZE(vmx->segment_cache.seg);
+	size_t index = array_index_nospec(seg, size);
+	u32 *p = &vmx->segment_cache.seg[index].limit;
 
 	if (!vmx_segment_cache_test_set(vmx, seg, SEG_FIELD_LIMIT))
 		*p = vmcs_read32(kvm_vmx_segment_fields[seg].limit);
@@ -780,7 +786,9 @@ static u32 vmx_read_guest_seg_limit(struct vcpu_vmx *vmx, unsigned seg)
 
 static u32 vmx_read_guest_seg_ar(struct vcpu_vmx *vmx, unsigned seg)
 {
-	u32 *p = &vmx->segment_cache.seg[seg].ar;
+	size_t size = ARRAY_SIZE(vmx->segment_cache.seg);
+	size_t index = array_index_nospec(seg, size);
+	u32 *p = &vmx->segment_cache.seg[index].ar;
 
 	if (!vmx_segment_cache_test_set(vmx, seg, SEG_FIELD_AR))
 		*p = vmcs_read32(kvm_vmx_segment_fields[seg].ar_bytes);
-- 
2.24.0.525.g8f36a354ae-goog