[PATCH 5.5 238/367] KVM: x86: Protect MSR-based index computations in fixed_msr_to_seg_unit() from Spectre-v1/L1TF attacks

Greg Kroah-Hartman
2020-02-10T12:59:13Z

From: Marios Pomonis <pomonis@google.com>

commit 25a5edea71b7c154b6a0b8cec14c711cafa31d26 upstream.

This fixes a Spectre-v1/L1TF vulnerability in fixed_msr_to_seg_unit().
This function contains index computations based on the
(attacker-controlled) MSR number.

Fixes: de9aef5e1ad6 ("KVM: MTRR: introduce fixed_mtrr_segment table")

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
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kvm/mtrr.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

--- a/arch/x86/kvm/mtrr.c
+++ b/arch/x86/kvm/mtrr.c
@@ -192,11 +192,15 @@ static bool fixed_msr_to_seg_unit(u32 ms
break;
case MSR_MTRRfix16K_80000 ... MSR_MTRRfix16K_A0000:
*seg = 1;
- *unit = msr - MSR_MTRRfix16K_80000;
+ *unit = array_index_nospec(
+ msr - MSR_MTRRfix16K_80000,
+ MSR_MTRRfix16K_A0000 - MSR_MTRRfix16K_80000 + 1);
break;
case MSR_MTRRfix4K_C0000 ... MSR_MTRRfix4K_F8000:
*seg = 2;
- *unit = msr - MSR_MTRRfix4K_C0000;
+ *unit = array_index_nospec(
+ msr - MSR_MTRRfix4K_C0000,
+ MSR_MTRRfix4K_F8000 - MSR_MTRRfix4K_C0000 + 1);
break;
default:
return false;