[PATCH v4] KVM: vmx: fix ept reserved bits for 1-GByte page

[PATCH v4] KVM: vmx: fix ept reserved bits for 1-GByte page

[Wanpeng Li]

EPT misconfig handler in kvm will check which reason lead to EPT
misconfiguration after vmexit. One of the reasons is that an EPT
paging-structure entry is configured with settings reserved for
future functionality. However, the handler can't identify if
paging-structure entry of reserved bits for 1-GByte page are
configured, since PDPTE which point to 1-GByte page will reserve
bits 29:12 instead of bits 7:3 which are reserved for PDPTE that
references an EPT Page Directory. This patch fix it by reserve
bits 29:12 for 1-GByte page.

Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
---
v3 -> v4:
 * don't mask bits 6:3 as reserved for 4K pages
v2 -> v3:
 * return 0xf8 for level == 4
 * check spte & (1ULL << 7) if level == 1
 * (rsvd_mask & 0x38) == 0 for large page or leaf page
v1 -> v2:
 * same "if" statement cover both 2MB and 1GB pages
 * return 0xf8 for level == 4
 * get the level by checking the return value of ept_rsvd_mask

---
 arch/x86/kvm/vmx.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index cad37d5..286c283 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -5521,17 +5521,18 @@ static u64 ept_rsvd_mask(u64 spte, int level)
 	for (i = 51; i > boot_cpu_data.x86_phys_bits; i--)
 		mask |= (1ULL << i);
 
-	if (level > 2)
+	if (level == 4)
 		/* bits 7:3 reserved */
 		mask |= 0xf8;
-	else if (level == 2) {
-		if (spte & (1ULL << 7))
-			/* 2MB ref, bits 20:12 reserved */
-			mask |= 0x1ff000;
-		else
-			/* bits 6:3 reserved */
-			mask |= 0x78;
-	}
+	else if (spte & (1ULL << 7))
+		/*
+		 * 1GB/2MB page, bits 29:12 or 20:12 reserved respectively,
+		 * level == 1 if the hypervisor is using the ignored bit 7.
+		 */
+		mask |= (PAGE_SIZE << ((level - 1) * 9)) - PAGE_SIZE;
+	else if (level > 1)
+		/* bits 6:3 reserved */
+		mask |= 0x78;
 
 	return mask;
 }
@@ -5561,7 +5562,8 @@ static void ept_misconfig_inspect_spte(struct kvm_vcpu *vcpu, u64 spte,
 			WARN_ON(1);
 		}
 
-		if (level == 1 || (level == 2 && (spte & (1ULL << 7)))) {
+		/* bits 5:3 are _not_ reserved for large page or leaf page */
+		if ((rsvd_bits & 0x38) == 0) {
 			u64 ept_mem_type = (spte & 0x38) >> 3;
 
 			if (ept_mem_type == 2 || ept_mem_type == 3 ||
-- 
1.9.1

Re: [PATCH v4] KVM: vmx: fix ept reserved bits for 1-GByte page

[Paolo Bonzini]

Il 20/08/2014 09:31, Wanpeng Li ha scritto:
> EPT misconfig handler in kvm will check which reason lead to EPT
> misconfiguration after vmexit. One of the reasons is that an EPT
> paging-structure entry is configured with settings reserved for
> future functionality. However, the handler can't identify if
> paging-structure entry of reserved bits for 1-GByte page are
> configured, since PDPTE which point to 1-GByte page will reserve
> bits 29:12 instead of bits 7:3 which are reserved for PDPTE that
> references an EPT Page Directory. This patch fix it by reserve
> bits 29:12 for 1-GByte page.

Thanks, the patch looks good.

Can you describe how you detected the problem and how you're testing for it?

Paolo

Re: [PATCH v4] KVM: vmx: fix ept reserved bits for 1-GByte page

[Wanpeng Li]

On Wed, Aug 20, 2014 at 10:13:07AM +0200, Paolo Bonzini wrote:
>Il 20/08/2014 09:31, Wanpeng Li ha scritto:
>> EPT misconfig handler in kvm will check which reason lead to EPT
>> misconfiguration after vmexit. One of the reasons is that an EPT
>> paging-structure entry is configured with settings reserved for
>> future functionality. However, the handler can't identify if
>> paging-structure entry of reserved bits for 1-GByte page are
>> configured, since PDPTE which point to 1-GByte page will reserve
>> bits 29:12 instead of bits 7:3 which are reserved for PDPTE that
>> references an EPT Page Directory. This patch fix it by reserve
>> bits 29:12 for 1-GByte page.
>
>Thanks, the patch looks good.
>
>Can you describe how you detected the problem and how you're testing for it?
>

I found the issue by reviewing codes.

Regards,
Wanpeng Li 

>Paolo