From d95c55687e11febe3ab1aacfe82b58b1822c52c4 Mon Sep 17 00:00:00 2001 From: Bandan Das Date: Tue, 12 Jul 2016 18:18:51 -0400 Subject: [PATCH] kvm: mmu: track read permission explicitly for shadow EPT page tables To support execute only mappings on behalf of L1 hypervisors, reuse ACC_USER_MASK to signify if the L1 hypervisor has the R bit set. For the nested EPT case, we assumed that the U bit was always set since there was no equivalent in EPT page tables. Strictly speaking, this was not necessary because handle_ept_violation never set PFERR_USER_MASK in the error code (uf=0 in the parlance of update_permission_bitmask). We now have to set both U and UF correctly, respectively in FNAME(gpte_access) and in handle_ept_violation. Also in handle_ept_violation bit 3 of the exit qualification is not enough to detect a present PTE; all three bits 3-5 have to be checked. Signed-off-by: Bandan Das Signed-off-by: Paolo Bonzini --- arch/x86/kvm/mmu.c | 10 +++++++--- arch/x86/kvm/paging_tmpl.h | 8 +++++++- arch/x86/kvm/vmx.c | 15 +++++++++------ 3 files changed, 23 insertions(+), 10 deletions(-) diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index b8628e905806..3041902ec827 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -2522,6 +2522,12 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep, if (set_mmio_spte(vcpu, sptep, gfn, pfn, pte_access)) return 0; + /* + * For the EPT case, shadow_present_mask is 0 if hardware + * supports exec-only page table entries. In that case, + * ACC_USER_MASK and shadow_user_mask are used to represent + * read access. See FNAME(gpte_access) in paging_tmpl.h. + */ spte |= shadow_present_mask; if (!speculative) spte |= shadow_accessed_mask; @@ -3915,9 +3921,7 @@ static void update_permission_bitmask(struct kvm_vcpu *vcpu, * 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) || (smapf && smap); diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h index fda5b64ae8f1..a01105485315 100644 --- a/arch/x86/kvm/paging_tmpl.h +++ b/arch/x86/kvm/paging_tmpl.h @@ -181,13 +181,19 @@ no_present: return true; } +/* + * For PTTYPE_EPT, a page table can be executable but not readable + * on supported processors. Therefore, set_spte does not automatically + * set bit 0 if execute only is supported. Here, we repurpose ACC_USER_MASK + * to signify readability since it isn't used in the EPT case + */ static inline unsigned FNAME(gpte_access)(struct kvm_vcpu *vcpu, u64 gpte) { unsigned access; #if PTTYPE == PTTYPE_EPT access = ((gpte & VMX_EPT_WRITABLE_MASK) ? ACC_WRITE_MASK : 0) | ((gpte & VMX_EPT_EXECUTABLE_MASK) ? ACC_EXEC_MASK : 0) | - ACC_USER_MASK; + ((gpte & VMX_EPT_READABLE_MASK) ? ACC_USER_MASK : 0); #else BUILD_BUG_ON(ACC_EXEC_MASK != PT_PRESENT_MASK); BUILD_BUG_ON(ACC_EXEC_MASK != 1); diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index a75d09d2a799..bd7d60f66b93 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -6117,12 +6117,14 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu) gpa = vmcs_read64(GUEST_PHYSICAL_ADDRESS); trace_kvm_page_fault(gpa, exit_qualification); - /* It is a write fault? */ - error_code = exit_qualification & PFERR_WRITE_MASK; + /* it is a read fault? */ + error_code = (exit_qualification << 2) & PFERR_USER_MASK; + /* it is a write fault? */ + error_code |= exit_qualification & PFERR_WRITE_MASK; /* It is a fetch fault? */ error_code |= (exit_qualification << 2) & PFERR_FETCH_MASK; /* ept page table is present? */ - error_code |= (exit_qualification >> 3) & PFERR_PRESENT_MASK; + error_code |= (exit_qualification & 0x38) != 0; vcpu->arch.exit_qualification = exit_qualification; @@ -6469,11 +6471,12 @@ static __init int hardware_setup(void) vmx_disable_intercept_msr_write_x2apic(0x83f); if (enable_ept) { - kvm_mmu_set_mask_ptes(0ull, + kvm_mmu_set_mask_ptes(VMX_EPT_READABLE_MASK, (enable_ept_ad_bits) ? VMX_EPT_ACCESS_BIT : 0ull, (enable_ept_ad_bits) ? VMX_EPT_DIRTY_BIT : 0ull, - 0ull, VMX_EPT_EXECUTABLE_MASK); - 0ull, VMX_EPT_EXECUTABLE_MASK, VMX_EPT_READABLE_MASK); + 0ull, VMX_EPT_EXECUTABLE_MASK, + cpu_has_vmx_ept_execute_only() ? + 0ull : VMX_EPT_READABLE_MASK); ept_set_mmio_spte_mask(); kvm_enable_tdp(); } else -- 2.39.5