[PATCH v3 2/5] KVM: MMU: check guest CR3 reserved bits based on its physical address width.

Yu Zhang
2017-08-24T12:51:42Z

Currently, KVM uses CR3_L_MODE_RESERVED_BITS to check the
reserved bits in CR3. Yet the length of reserved bits in
guest CR3 should be based on the physical address width
exposed to the VM. This patch changes CR3 check logic to
calculate the reserved bits at runtime.

Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
---
arch/x86/include/asm/kvm_host.h | 1 -
arch/x86/kvm/emulate.c | 14 ++++++++++++--
arch/x86/kvm/mmu.h | 3 +++
arch/x86/kvm/x86.c | 8 ++++----
4 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 6db0ed9..e716228 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -79,7 +79,6 @@
| X86_CR0_ET | X86_CR0_NE | X86_CR0_WP | X86_CR0_AM \
| X86_CR0_NW | X86_CR0_CD | X86_CR0_PG))

-#define CR3_L_MODE_RESERVED_BITS 0xFFFFFF0000000000ULL
#define CR3_PCID_INVD BIT_64(63)
#define CR4_RESERVED_BITS \
(~(unsigned long)(X86_CR4_VME | X86_CR4_PVI | X86_CR4_TSD | X86_CR4_DE\
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 319d91f..a89b595 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -28,6 +28,7 @@

#include "x86.h"
#include "tss.h"
+#include "mmu.h"

/*
* Operand types
@@ -4097,8 +4098,17 @@ static int check_cr_write(struct x86_emulate_ctxt *ctxt)
u64 rsvd = 0;

ctxt->ops->get_msr(ctxt, MSR_EFER, &efer);
- if (efer & EFER_LMA)
- rsvd = CR3_L_MODE_RESERVED_BITS & ~CR3_PCID_INVD;
+ if (efer & EFER_LMA) {
+ u64 maxphyaddr;
+ u32 eax = 0x80000008;
+
+ if (ctxt->ops->get_cpuid(ctxt, &eax, NULL, NULL,
+ NULL, false))
+ maxphyaddr = eax & 0xff;
+ else
+ maxphyaddr = 36;
+ rsvd = rsvd_bits(maxphyaddr, 62);
+ }

if (new_val & rsvd)
return emulate_gp(ctxt, 0);
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 3ed6192..67e7ec2 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -48,6 +48,9 @@

static inline u64 rsvd_bits(int s, int e)
{
+ if (e < s)
+ return 0;
+
return ((1ULL << (e - s + 1)) - 1) << s;
}

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index cc2c7e4..79f5889 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -813,10 +813,10 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
return 0;
}

- if (is_long_mode(vcpu)) {
- if (cr3 & CR3_L_MODE_RESERVED_BITS)
- return 1;
- } else if (is_pae(vcpu) && is_paging(vcpu) &&
+ if (is_long_mode(vcpu) &&
+ (cr3 & rsvd_bits(cpuid_maxphyaddr(vcpu), 62)))
+ return 1;
+ else if (is_pae(vcpu) && is_paging(vcpu) &&
!load_pdptrs(vcpu, vcpu->arch.walk_mmu, cr3))
return 1;

--
2.5.0