[PATCH v4 4/6] KVM: x86: Make use of kvm_read_cr*_bits() when testing bits

Mathias Krause
2023-03-22T01:34:47Z

Make use of the kvm_read_cr{0,4}_bits() helper functions when we only
want to know the state of certain bits instead of the whole register.

This not only makes the intent cleaner, it also avoids a potential
VMREAD in case the tested bits aren't guest owned.

Signed-off-by: Mathias Krause <minipli@grsecurity.net>
---
arch/x86/kvm/pmu.c | 4 ++--
arch/x86/kvm/vmx/vmx.c | 4 ++--
2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index 612e6c70ce2e..f4aa170b5b97 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -540,9 +540,9 @@ int kvm_pmu_rdpmc(struct kvm_vcpu *vcpu, unsigned idx, u64 *data)
if (!pmc)
return 1;

- if (!(kvm_read_cr4(vcpu) & X86_CR4_PCE) &&
+ if (!(kvm_read_cr4_bits(vcpu, X86_CR4_PCE)) &&
(static_call(kvm_x86_get_cpl)(vcpu) != 0) &&
- (kvm_read_cr0(vcpu) & X86_CR0_PE))
+ (kvm_read_cr0_bits(vcpu, X86_CR0_PE)))
return 1;

*data = pmc_read_counter(pmc) & mask;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index d7bf14abdba1..8fc1a0c7856f 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5517,7 +5517,7 @@ static int handle_cr(struct kvm_vcpu *vcpu)
break;
case 3: /* lmsw */
val = (exit_qualification >> LMSW_SOURCE_DATA_SHIFT) & 0x0f;
- trace_kvm_cr_write(0, (kvm_read_cr0(vcpu) & ~0xful) | val);
+ trace_kvm_cr_write(0, (kvm_read_cr0_bits(vcpu, ~0xful) | val));
kvm_lmsw(vcpu, val);

return kvm_skip_emulated_instruction(vcpu);
@@ -7575,7 +7575,7 @@ static u8 vmx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
if (!kvm_arch_has_noncoherent_dma(vcpu->kvm))
return (MTRR_TYPE_WRBACK << VMX_EPT_MT_EPTE_SHIFT) | VMX_EPT_IPAT_BIT;

- if (kvm_read_cr0(vcpu) & X86_CR0_CD) {
+ if (kvm_read_cr0_bits(vcpu, X86_CR0_CD)) {
if (kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_CD_NW_CLEARED))
cache = MTRR_TYPE_WRBACK;
else
--
2.39.2