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KVM: Add SMAP support when setting CR4

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This patch adds SMAP handling logic when setting CR4 for guests

Thanks a lot to Paolo Bonzini for his suggestion to use the branchless
way to detect SMAP violation.

Signed-off-by: Feng Wu <feng.wu@intel.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Feng Wu 2014-04-01 17:46:34 +08:00 committed by Marcelo Tosatti
parent 56d6efc2de
commit 97ec8c067d
5 changed files with 84 additions and 13 deletions
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8
arch/x86/kvm/cpuid.h
View File

@ -48,6 +48,14 @@ static inline bool guest_cpuid_has_smep(struct kvm_vcpu *vcpu)
return best && (best->ebx & bit(X86_FEATURE_SMEP));
}
static inline bool guest_cpuid_has_smap(struct kvm_vcpu *vcpu)
{
struct kvm_cpuid_entry2 *best;
best = kvm_find_cpuid_entry(vcpu, 7, 0);
return best && (best->ebx & bit(X86_FEATURE_SMAP));
}
static inline bool guest_cpuid_has_fsgsbase(struct kvm_vcpu *vcpu)
{
struct kvm_cpuid_entry2 *best;

34
arch/x86/kvm/mmu.c
View File

@ -3601,20 +3601,27 @@ static void reset_rsvds_bits_mask_ept(struct kvm_vcpu *vcpu,
}
}
static void update_permission_bitmask(struct kvm_vcpu *vcpu,
void update_permission_bitmask(struct kvm_vcpu *vcpu,
struct kvm_mmu *mmu, bool ept)
{
unsigned bit, byte, pfec;
u8 map;
bool fault, x, w, u, wf, uf, ff, smep;
bool fault, x, w, u, wf, uf, ff, smapf, cr4_smap, smep, smap = 0;
smep = kvm_read_cr4_bits(vcpu, X86_CR4_SMEP);
cr4_smap = kvm_read_cr4_bits(vcpu, X86_CR4_SMAP);
for (byte = 0; byte < ARRAY_SIZE(mmu->permissions); ++byte) {
pfec = byte << 1;
map = 0;
wf = pfec & PFERR_WRITE_MASK;
uf = pfec & PFERR_USER_MASK;
ff = pfec & PFERR_FETCH_MASK;
/*
* PFERR_RSVD_MASK bit is set in PFEC if the access is not
* subject to SMAP restrictions, and cleared otherwise. The
* bit is only meaningful if the SMAP bit is set in CR4.
*/
smapf = !(pfec & PFERR_RSVD_MASK);
for (bit = 0; bit < 8; ++bit) {
x = bit & ACC_EXEC_MASK;
w = bit & ACC_WRITE_MASK;
@ -3627,11 +3634,32 @@ static void update_permission_bitmask(struct kvm_vcpu *vcpu,
w |= !is_write_protection(vcpu) && !uf;
/* Disallow supervisor fetches of user code if cr4.smep */
x &= !(smep && u && !uf);
/*
* SMAP:kernel-mode data accesses from user-mode
* mappings should fault. A fault is considered
* as a SMAP violation if all of the following
* conditions are ture:
* - X86_CR4_SMAP is set in CR4
* - An user page is accessed
* - Page fault in kernel mode
* - if CPL = 3 or X86_EFLAGS_AC is clear
*
* Here, we cover the first three conditions.
* The fourth is computed dynamically in
* permission_fault() and is in smapf.
*
* Also, SMAP does not affect instruction
* fetches, add the !ff check here to make it
* clearer.
*/
smap = cr4_smap && u && !uf && !ff;
} else
/* Not really needed: no U/S accesses on ept */
u = 1;
fault = (ff && !x) || (uf && !u) || (wf && !w);
fault = (ff && !x) || (uf && !u) || (wf && !w) ||
(smapf && smap);
map |= fault << bit;
}
mmu->permissions[byte] = map;

44
arch/x86/kvm/mmu.h
View File

@ -44,11 +44,17 @@
#define PT_DIRECTORY_LEVEL 2
#define PT_PAGE_TABLE_LEVEL 1
#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 PFERR_PRESENT_BIT 0
#define PFERR_WRITE_BIT 1
#define PFERR_USER_BIT 2
#define PFERR_RSVD_BIT 3
#define PFERR_FETCH_BIT 4
#define PFERR_PRESENT_MASK (1U << PFERR_PRESENT_BIT)
#define PFERR_WRITE_MASK (1U << PFERR_WRITE_BIT)
#define PFERR_USER_MASK (1U << PFERR_USER_BIT)
#define PFERR_RSVD_MASK (1U << PFERR_RSVD_BIT)
#define PFERR_FETCH_MASK (1U << PFERR_FETCH_BIT)
int kvm_mmu_get_spte_hierarchy(struct kvm_vcpu *vcpu, u64 addr, u64 sptes[4]);
void kvm_mmu_set_mmio_spte_mask(u64 mmio_mask);
@ -73,6 +79,8 @@ int handle_mmio_page_fault_common(struct kvm_vcpu *vcpu, u64 addr, bool direct);
void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu, struct kvm_mmu *context);
void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, struct kvm_mmu *context,
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)
{
@ -110,10 +118,30 @@ static inline bool is_write_protection(struct kvm_vcpu *vcpu)
* Will a fault with a given page-fault error code (pfec) cause a permission
* fault with the given access (in ACC_* format)?
*/
static inline bool permission_fault(struct kvm_mmu *mmu, unsigned pte_access,
unsigned pfec)
static inline bool permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
unsigned pte_access, unsigned pfec)
{
return (mmu->permissions[pfec >> 1] >> pte_access) & 1;
int cpl = kvm_x86_ops->get_cpl(vcpu);
unsigned long rflags = kvm_x86_ops->get_rflags(vcpu);
/*
* If CPL < 3, SMAP prevention are disabled if EFLAGS.AC = 1.
*
* If CPL = 3, SMAP applies to all supervisor-mode data accesses
* (these are implicit supervisor accesses) regardless of the value
* of EFLAGS.AC.
*
* This computes (cpl < 3) && (rflags & X86_EFLAGS_AC), leaving
* the result in X86_EFLAGS_AC. We then insert it in place of
* the PFERR_RSVD_MASK bit; this bit will always be zero in pfec,
* but it will be one in index if SMAP checks are being overridden.
* It is important to keep this branchless.
*/
unsigned long smap = (cpl - 3) & (rflags & X86_EFLAGS_AC);
int index = (pfec >> 1) +
(smap >> (X86_EFLAGS_AC_BIT - PFERR_RSVD_BIT + 1));
return (mmu->permissions[index] >> pte_access) & 1;
}
void kvm_mmu_invalidate_zap_all_pages(struct kvm *kvm);

2
arch/x86/kvm/paging_tmpl.h
View File

@ -353,7 +353,7 @@ retry_walk:
walker->ptes[walker->level - 1] = pte;
} while (!is_last_gpte(mmu, walker->level, pte));
if (unlikely(permission_fault(mmu, pte_access, access))) {
if (unlikely(permission_fault(vcpu, mmu, pte_access, access))) {
errcode |= PFERR_PRESENT_MASK;
goto error;
}

9
arch/x86/kvm/x86.c
View File

@ -652,6 +652,9 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
if (!guest_cpuid_has_smep(vcpu) && (cr4 & X86_CR4_SMEP))
return 1;
if (!guest_cpuid_has_smap(vcpu) && (cr4 & X86_CR4_SMAP))
return 1;
if (!guest_cpuid_has_fsgsbase(vcpu) && (cr4 & X86_CR4_FSGSBASE))
return 1;
@ -680,6 +683,9 @@ 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);
@ -4164,7 +4170,8 @@ static int vcpu_mmio_gva_to_gpa(struct kvm_vcpu *vcpu, unsigned long gva,
| (write ? PFERR_WRITE_MASK : 0);
if (vcpu_match_mmio_gva(vcpu, gva)
&& !permission_fault(vcpu->arch.walk_mmu, vcpu->arch.access, access)) {
&& !permission_fault(vcpu, vcpu->arch.walk_mmu,
vcpu->arch.access, access)) {
*gpa = vcpu->arch.mmio_gfn << PAGE_SHIFT |
(gva & (PAGE_SIZE - 1));
trace_vcpu_match_mmio(gva, *gpa, write, false);