RFC: Add reserved bits check

Commit Message

Dong, Eddie March 27, 2009, 2:42 p.m. UTC

> 
> Need to make sure rsvd_bits_mask[] is maintained on ept and npt, then.

Sure, will be in next patch, post the current modified one.

Thx, eddie



Current KVM doesn't check reserved bits of guest page table entry, but use reserved bits to bypass guest #PF in VMX.

 

This patch add reserved bit check while leaving shadow pte un-constructed if guest RSVD=1.


commit dd1d697edf42953d407c10f4d38c650aafd3d3d5
Author: root <[e-mail]>
Date:   Fri Mar 27 23:35:27 2009 +0800

    Emulate #PF error code of reserved bits violation.
    
    Signed-off-by: Eddie Dong <[e-mail]>

Comments

Avi Kivity March 29, 2009, 10:23 a.m. UTC | #1

Dong, Eddie wrote:
>  
> +static bool is_rsvd_bits_set(struct kvm_vcpu *vcpu, u64 gpte, int level)
> +{
> +	int ps = 0;
> +
> +	if (level == PT_DIRECTORY_LEVEL)
> +		ps = !!(gpte & PT_PAGE_SIZE_MASK);
>   

No need for this.  If you set rsvd_bits_mask[1][0] == 
rsvd_bits_mask[0][0], then you get the same behaviour.  The first index 
is not the page size, it's just bit 7.

You'll need to fill all the indexes for bit 7 == 1, but it's worth it, 
with the 1GB pages patch.

> +	return (gpte & vcpu->arch.mmu.rsvd_bits_mask[ps][level-1]) != 0;
> +}
> +
>  #define PTTYPE 64
>  #include "paging_tmpl.h"
>  #undef PTTYPE
>  
> +int cpuid_maxphyaddr(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm_cpuid_entry2 *best;
> +
> +	best = kvm_find_cpuid_entry(vcpu, 0x80000008, 0);
> +	if (best)
> +		return best->eax & 0xff;
> +	return 32;
> +}
> +
>   

Best to return 36 if the cpu doesn't support cpuid 80000008 but does 
support pae.

Patch

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 55fd4c5..4fe2742 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -261,6 +261,7 @@  struct kvm_mmu {
 	union kvm_mmu_page_role base_role;
 
 	u64 *pae_root;
+	u64 rsvd_bits_mask[2][4];
 };
 
 struct kvm_vcpu_arch {
@@ -791,5 +792,6 @@  asmlinkage void kvm_handle_fault_on_reboot(void);
 #define KVM_ARCH_WANT_MMU_NOTIFIER
 int kvm_unmap_hva(struct kvm *kvm, unsigned long hva);
 int kvm_age_hva(struct kvm *kvm, unsigned long hva);
+int cpuid_maxphyaddr(struct kvm_vcpu *vcpu);
 
 #endif /* _ASM_X86_KVM_HOST_H */
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index ef060ec..35af90a 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -126,6 +126,7 @@  module_param(oos_shadow, bool, 0644);
 #define PFERR_PRESENT_MASK (1U << 0)
 #define PFERR_WRITE_MASK (1U << 1)
 #define PFERR_USER_MASK (1U << 2)
+#define PFERR_RSVD_MASK (1U << 3)
 #define PFERR_FETCH_MASK (1U << 4)
 
 #define PT_DIRECTORY_LEVEL 2
@@ -179,6 +180,11 @@  static u64 __read_mostly shadow_accessed_mask;
 static u64 __read_mostly shadow_dirty_mask;
 static u64 __read_mostly shadow_mt_mask;
 
+static inline u64 rsvd_bits(int s, int e)
+{
+	return ((1ULL << (e - s + 1)) - 1) << s;
+}
+
 void kvm_mmu_set_nonpresent_ptes(u64 trap_pte, u64 notrap_pte)
 {
 	shadow_trap_nonpresent_pte = trap_pte;
@@ -2155,6 +2161,15 @@  static void paging_free(struct kvm_vcpu *vcpu)
 	nonpaging_free(vcpu);
 }
 
+static bool is_rsvd_bits_set(struct kvm_vcpu *vcpu, u64 gpte, int level)
+{
+	int ps = 0;
+
+	if (level == PT_DIRECTORY_LEVEL)
+		ps = !!(gpte & PT_PAGE_SIZE_MASK);
+	return (gpte & vcpu->arch.mmu.rsvd_bits_mask[ps][level-1]) != 0;
+}
+
 #define PTTYPE 64
 #include "paging_tmpl.h"
 #undef PTTYPE
@@ -2183,6 +2198,22 @@  static int paging64_init_context_common(struct kvm_vcpu *vcpu, int level)
 
 static int paging64_init_context(struct kvm_vcpu *vcpu)
 {
+	struct kvm_mmu *context = &vcpu->arch.mmu;
+	int maxphyaddr = cpuid_maxphyaddr(vcpu);
+	u64 exb_bit_rsvd = 0;
+
+	if (!is_nx(vcpu))
+		exb_bit_rsvd = rsvd_bits(63, 63);
+
+	context->rsvd_bits_mask[0][3] = exb_bit_rsvd |
+		rsvd_bits(maxphyaddr, 51) | rsvd_bits(7, 8);
+	context->rsvd_bits_mask[0][2] = exb_bit_rsvd |
+		rsvd_bits(maxphyaddr, 51) | rsvd_bits(7, 8);
+	context->rsvd_bits_mask[0][1] = exb_bit_rsvd |
+		rsvd_bits(maxphyaddr, 51) | rsvd_bits(7, 8);
+	context->rsvd_bits_mask[0][0] = rsvd_bits(maxphyaddr, 51);
+	context->rsvd_bits_mask[1][1] = exb_bit_rsvd |
+		rsvd_bits(maxphyaddr, 51) | rsvd_bits(13, 20);
 	return paging64_init_context_common(vcpu, PT64_ROOT_LEVEL);
 }
 
@@ -2190,6 +2221,15 @@  static int paging32_init_context(struct kvm_vcpu *vcpu)
 {
 	struct kvm_mmu *context = &vcpu->arch.mmu;
 
+	/* no rsvd bits for 2 level 4K page table entries */
+	context->rsvd_bits_mask[0][0] = 0;
+	context->rsvd_bits_mask[0][1] = 0;
+	if (is_cpuid_PSE36())
+		/* 36bits PSE 4MB page */
+		context->rsvd_bits_mask[1][1] = rsvd_bits(17, 21);
+	else
+		/* 32 bits PSE 4MB page */
+		context->rsvd_bits_mask[1][1] = rsvd_bits(13, 21);
 	context->new_cr3 = paging_new_cr3;
 	context->page_fault = paging32_page_fault;
 	context->gva_to_gpa = paging32_gva_to_gpa;
@@ -2205,6 +2245,21 @@  static int paging32_init_context(struct kvm_vcpu *vcpu)
 
 static int paging32E_init_context(struct kvm_vcpu *vcpu)
 {
+	struct kvm_mmu *context = &vcpu->arch.mmu;
+	int maxphyaddr = cpuid_maxphyaddr(vcpu);
+	u64 exb_bit_rsvd = 0;
+
+	if (!is_nx(vcpu))
+		exb_bit_rsvd = rsvd_bits(63, 63);
+
+	context->rsvd_bits_mask[0][1] = exb_bit_rsvd |
+		rsvd_bits(maxphyaddr, 62);		/* PDE */
+	context->rsvd_bits_mask[0][0] = exb_bit_rsvd |
+			rsvd_bits(maxphyaddr, 62); 	/* PTE */
+	context->rsvd_bits_mask[1][1] = exb_bit_rsvd |
+			rsvd_bits(maxphyaddr, 62) |
+			rsvd_bits(13, 20);		/* large page */
+
 	return paging64_init_context_common(vcpu, PT32E_ROOT_LEVEL);
 }
 
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 7314c09..3bf1345 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -123,6 +123,7 @@  static int FNAME(walk_addr)(struct guest_walker *walker,
 	gfn_t table_gfn;
 	unsigned index, pt_access, pte_access;
 	gpa_t pte_gpa;
+	int rsvd_fault = 0;
 
 	pgprintk("%s: addr %lx\n", __func__, addr);
 walk:
@@ -153,10 +154,13 @@  walk:
 			 walker->level - 1, table_gfn);
 
 		kvm_read_guest(vcpu->kvm, pte_gpa, &pte, sizeof(pte));
+		rsvd_fault = is_rsvd_bits_set(vcpu, pte, walker->level);
 
 		if (!is_present_pte(pte))
 			goto not_present;
 
+		if (rsvd_fault)
+			goto access_error;
 		if (write_fault && !is_writeble_pte(pte))
 			if (user_fault || is_write_protection(vcpu))
 				goto access_error;
@@ -233,6 +237,8 @@  err:
 		walker->error_code |= PFERR_USER_MASK;
 	if (fetch_fault)
 		walker->error_code |= PFERR_FETCH_MASK;
+	if (rsvd_fault)
+		walker->error_code |= PFERR_RSVD_MASK;
 	return 0;
 }
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e96edda..2c6f180 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2899,6 +2899,16 @@  struct kvm_cpuid_entry2 *kvm_find_cpuid_entry(struct kvm_vcpu *vcpu,
 	return best;
 }
 
+int cpuid_maxphyaddr(struct kvm_vcpu *vcpu)
+{
+	struct kvm_cpuid_entry2 *best;
+
+	best = kvm_find_cpuid_entry(vcpu, 0x80000008, 0);
+	if (best)
+		return best->eax & 0xff;
+	return 32;
+}
+
 void kvm_emulate_cpuid(struct kvm_vcpu *vcpu)
 {
 	u32 function, index;