From 97ec8c067d322d32effdc1701760d3babbc5595f Mon Sep 17 00:00:00 2001 From: Feng Wu Date: Tue, 1 Apr 2014 17:46:34 +0800 Subject: [PATCH] KVM: Add SMAP support when setting CR4 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 Signed-off-by: Marcelo Tosatti --- arch/x86/kvm/cpuid.h | 8 +++++++ arch/x86/kvm/mmu.c | 34 ++++++++++++++++++++++++++--- arch/x86/kvm/mmu.h | 44 +++++++++++++++++++++++++++++++------- arch/x86/kvm/paging_tmpl.h | 2 +- arch/x86/kvm/x86.c | 9 +++++++- 5 files changed, 84 insertions(+), 13 deletions(-) diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h index a2a1bb7ed8c1..eeecbed26ac7 100644 --- a/arch/x86/kvm/cpuid.h +++ b/arch/x86/kvm/cpuid.h @@ -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; diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index f5704d9e5ddc..084caf3efaf5 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -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; diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h index 292615274358..3842e70bdb7c 100644 --- a/arch/x86/kvm/mmu.h +++ b/arch/x86/kvm/mmu.h @@ -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); diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h index b1e6c1bf68d3..123efd3ec29f 100644 --- a/arch/x86/kvm/paging_tmpl.h +++ b/arch/x86/kvm/paging_tmpl.h @@ -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; } diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index d1c55f8722c6..41693787cd66 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -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);