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Subject[PATCH v2 2/3] KVM: MMU: fix SMAP virtualization

From: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Date: Mon, 11 May 2015 21:09:15 +0800
Subject: [PATCH] KVM: MMU: fix SMAP virtualization

KVM may turn a user page to a kernel page when kernel writes a readonly
user page if CR0.WP = 1. This shadow page entry will be reused after
SMAP is enabled so that kernel is allowed to access this user page

Fix it by setting SMAP && !CR0.WP into shadow page's role and reset mmu
once CR4.SMAP is updated

Changelog in v2:
- rebase the patch against the commit 31fd9880a1c5 (Paolo Bonzini:
KVM: MMU: fix CR4.SMEP=1, CR0.WP=0 with shadow pages)
- do not prefetch the spte if it does not match smap_andnot_wp with
current vcpu

Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/mmu.c | 16 ++++++++++++----
arch/x86/kvm/mmu.h | 2 --
arch/x86/kvm/x86.c | 8 +++-----
4 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 8b661d1..bbb8f4e 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -207,6 +207,7 @@ union kvm_mmu_page_role {
unsigned nxe:1;
unsigned cr0_wp:1;
unsigned smep_andnot_wp:1;
+ unsigned smap_andnot_wp:1;
};
};

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 3711095..4058a6b 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3737,8 +3737,8 @@ static void reset_rsvds_bits_mask_ept(struct kvm_vcpu *vcpu,
}
}

-void update_permission_bitmask(struct kvm_vcpu *vcpu,
- struct kvm_mmu *mmu, bool ept)
+static void update_permission_bitmask(struct kvm_vcpu *vcpu,
+ struct kvm_mmu *mmu, bool ept)
{
unsigned bit, byte, pfec;
u8 map;
@@ -3919,6 +3919,7 @@ static void init_kvm_tdp_mmu(struct kvm_vcpu *vcpu)
void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu)
{
bool smep = kvm_read_cr4_bits(vcpu, X86_CR4_SMEP);
+ bool smap = kvm_read_cr4_bits(vcpu, X86_CR4_SMAP);
struct kvm_mmu *context = &vcpu->arch.mmu;

MMU_WARN_ON(VALID_PAGE(context->root_hpa));
@@ -3937,6 +3938,8 @@ void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu)
context->base_role.cr0_wp = is_write_protection(vcpu);
context->base_role.smep_andnot_wp
= smep && !is_write_protection(vcpu);
+ context->base_role.smap_andnot_wp
+ = smap && !is_write_protection(vcpu);
}
EXPORT_SYMBOL_GPL(kvm_init_shadow_mmu);

@@ -4208,12 +4211,18 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
const u8 *new, int bytes)
{
gfn_t gfn = gpa >> PAGE_SHIFT;
- union kvm_mmu_page_role mask = { .word = 0 };
struct kvm_mmu_page *sp;
LIST_HEAD(invalid_list);
u64 entry, gentry, *spte;
int npte;
bool remote_flush, local_flush, zap_page;
+ union kvm_mmu_page_role mask = (union kvm_mmu_page_role) {
+ .cr0_wp = 1,
+ .cr4_pae = 1,
+ .nxe = 1,
+ .smep_andnot_wp = 1,
+ .smap_andnot_wp = 1,
+ };

/*
* If we don't have indirect shadow pages, it means no page is
@@ -4239,7 +4248,6 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
++vcpu->kvm->stat.mmu_pte_write;
kvm_mmu_audit(vcpu, AUDIT_PRE_PTE_WRITE);

- mask.cr0_wp = mask.cr4_pae = mask.nxe = mask.smep_andnot_wp = 1;
for_each_gfn_indirect_valid_sp(vcpu->kvm, sp, gfn) {
if (detect_write_misaligned(sp, gpa, bytes) ||
detect_write_flooding(sp)) {
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 06eb2fc..0ada65e 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -71,8 +71,6 @@ enum {
int handle_mmio_page_fault_common(struct kvm_vcpu *vcpu, u64 addr, bool direct);
void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu);
void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly);
-void update_permission_bitmask(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
- bool ept);

static inline unsigned int kvm_mmu_available_pages(struct kvm *kvm)
{
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index cdccbe1..cde5d61 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -702,8 +702,9 @@ EXPORT_SYMBOL_GPL(kvm_set_xcr);
int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
{
unsigned long old_cr4 = kvm_read_cr4(vcpu);
- unsigned long pdptr_bits = X86_CR4_PGE | X86_CR4_PSE |
- X86_CR4_PAE | X86_CR4_SMEP;
+ unsigned long pdptr_bits = X86_CR4_PGE | X86_CR4_PSE | X86_CR4_PAE |
+ X86_CR4_SMEP | X86_CR4_SMAP;
+
if (cr4 & CR4_RESERVED_BITS)
return 1;

@@ -744,9 +745,6 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
(!(cr4 & X86_CR4_PCIDE) && (old_cr4 & X86_CR4_PCIDE)))
kvm_mmu_reset_context(vcpu);

- if ((cr4 ^ old_cr4) & X86_CR4_SMAP)
- update_permission_bitmask(vcpu, vcpu->arch.walk_mmu, false);
-
if ((cr4 ^ old_cr4) & X86_CR4_OSXSAVE)
kvm_update_cpuid(vcpu);

--
2.1.0


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