diff options
Diffstat (limited to 'arch/x86/kvm/mmu/spte.c')
| -rw-r--r-- | arch/x86/kvm/mmu/spte.c | 576 |
1 files changed, 576 insertions, 0 deletions
diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c new file mode 100644 index 000000000000..85a0473809b0 --- /dev/null +++ b/arch/x86/kvm/mmu/spte.c @@ -0,0 +1,576 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Kernel-based Virtual Machine driver for Linux + * + * Macros and functions to access KVM PTEs (also known as SPTEs) + * + * Copyright (C) 2006 Qumranet, Inc. + * Copyright 2020 Red Hat, Inc. and/or its affiliates. + */ +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include <linux/kvm_host.h> +#include "mmu.h" +#include "mmu_internal.h" +#include "x86.h" +#include "spte.h" + +#include <asm/e820/api.h> +#include <asm/memtype.h> +#include <asm/vmx.h> + +bool __read_mostly enable_mmio_caching = true; +static bool __ro_after_init allow_mmio_caching; +module_param_named(mmio_caching, enable_mmio_caching, bool, 0444); +EXPORT_SYMBOL_FOR_KVM_INTERNAL(enable_mmio_caching); + +bool __read_mostly kvm_ad_enabled; + +u64 __read_mostly shadow_host_writable_mask; +u64 __read_mostly shadow_mmu_writable_mask; +u64 __read_mostly shadow_nx_mask; +u64 __read_mostly shadow_x_mask; /* mutual exclusive with nx_mask */ +u64 __read_mostly shadow_user_mask; +u64 __read_mostly shadow_accessed_mask; +u64 __read_mostly shadow_dirty_mask; +u64 __read_mostly shadow_mmio_value; +u64 __read_mostly shadow_mmio_mask; +u64 __read_mostly shadow_mmio_access_mask; +u64 __read_mostly shadow_present_mask; +u64 __read_mostly shadow_me_value; +u64 __read_mostly shadow_me_mask; +u64 __read_mostly shadow_acc_track_mask; + +u64 __read_mostly shadow_nonpresent_or_rsvd_mask; +u64 __read_mostly shadow_nonpresent_or_rsvd_lower_gfn_mask; + +static u8 __init kvm_get_host_maxphyaddr(void) +{ + /* + * boot_cpu_data.x86_phys_bits is reduced when MKTME or SME are detected + * in CPU detection code, but the processor treats those reduced bits as + * 'keyID' thus they are not reserved bits. Therefore KVM needs to look at + * the physical address bits reported by CPUID, i.e. the raw MAXPHYADDR, + * when reasoning about CPU behavior with respect to MAXPHYADDR. + */ + if (likely(boot_cpu_data.extended_cpuid_level >= 0x80000008)) + return cpuid_eax(0x80000008) & 0xff; + + /* + * Quite weird to have VMX or SVM but not MAXPHYADDR; probably a VM with + * custom CPUID. Proceed with whatever the kernel found since these features + * aren't virtualizable (SME/SEV also require CPUIDs higher than 0x80000008). + */ + return boot_cpu_data.x86_phys_bits; +} + +void __init kvm_mmu_spte_module_init(void) +{ + /* + * Snapshot userspace's desire to allow MMIO caching. Whether or not + * KVM can actually enable MMIO caching depends on vendor-specific + * hardware capabilities and other module params that can't be resolved + * until the vendor module is loaded, i.e. enable_mmio_caching can and + * will change when the vendor module is (re)loaded. + */ + allow_mmio_caching = enable_mmio_caching; + + kvm_host.maxphyaddr = kvm_get_host_maxphyaddr(); +} + +static u64 generation_mmio_spte_mask(u64 gen) +{ + u64 mask; + + WARN_ON_ONCE(gen & ~MMIO_SPTE_GEN_MASK); + + mask = (gen << MMIO_SPTE_GEN_LOW_SHIFT) & MMIO_SPTE_GEN_LOW_MASK; + mask |= (gen << MMIO_SPTE_GEN_HIGH_SHIFT) & MMIO_SPTE_GEN_HIGH_MASK; + return mask; +} + +u64 make_mmio_spte(struct kvm_vcpu *vcpu, u64 gfn, unsigned int access) +{ + u64 gen = kvm_vcpu_memslots(vcpu)->generation & MMIO_SPTE_GEN_MASK; + u64 spte = generation_mmio_spte_mask(gen); + u64 gpa = gfn << PAGE_SHIFT; + + access &= shadow_mmio_access_mask; + spte |= vcpu->kvm->arch.shadow_mmio_value | access; + spte |= gpa | shadow_nonpresent_or_rsvd_mask; + spte |= (gpa & shadow_nonpresent_or_rsvd_mask) + << SHADOW_NONPRESENT_OR_RSVD_MASK_LEN; + + return spte; +} + +static bool __kvm_is_mmio_pfn(kvm_pfn_t pfn) +{ + if (pfn_valid(pfn)) + return !is_zero_pfn(pfn) && PageReserved(pfn_to_page(pfn)) && + /* + * Some reserved pages, such as those from NVDIMM + * DAX devices, are not for MMIO, and can be mapped + * with cached memory type for better performance. + * However, the above check misconceives those pages + * as MMIO, and results in KVM mapping them with UC + * memory type, which would hurt the performance. + * Therefore, we check the host memory type in addition + * and only treat UC/UC-/WC pages as MMIO. + */ + (!pat_enabled() || pat_pfn_immune_to_uc_mtrr(pfn)); + + return !e820__mapped_raw_any(pfn_to_hpa(pfn), + pfn_to_hpa(pfn + 1) - 1, + E820_TYPE_RAM); +} + +static bool kvm_is_mmio_pfn(kvm_pfn_t pfn, int *is_host_mmio) +{ + /* + * Determining if a PFN is host MMIO is relative expensive. Cache the + * result locally (in the sole caller) to avoid doing the full query + * multiple times when creating a single SPTE. + */ + if (*is_host_mmio < 0) + *is_host_mmio = __kvm_is_mmio_pfn(pfn); + + return *is_host_mmio; +} + +static void kvm_track_host_mmio_mapping(struct kvm_vcpu *vcpu) +{ + struct kvm_mmu_page *root = root_to_sp(vcpu->arch.mmu->root.hpa); + + if (root) + WRITE_ONCE(root->has_mapped_host_mmio, true); + else + WRITE_ONCE(vcpu->kvm->arch.has_mapped_host_mmio, true); + + /* + * Force vCPUs to exit and flush CPU buffers if the vCPU is using the + * affected root(s). + */ + kvm_make_all_cpus_request(vcpu->kvm, KVM_REQ_OUTSIDE_GUEST_MODE); +} + +/* + * Returns true if the SPTE needs to be updated atomically due to having bits + * that may be changed without holding mmu_lock, and for which KVM must not + * lose information. E.g. KVM must not drop Dirty bit information. The caller + * is responsible for checking if the SPTE is shadow-present, and for + * determining whether or not the caller cares about non-leaf SPTEs. + */ +bool spte_needs_atomic_update(u64 spte) +{ + /* SPTEs can be made Writable bit by KVM's fast page fault handler. */ + if (!is_writable_pte(spte) && is_mmu_writable_spte(spte)) + return true; + + /* + * A/D-disabled SPTEs can be access-tracked by aging, and access-tracked + * SPTEs can be restored by KVM's fast page fault handler. + */ + if (!spte_ad_enabled(spte)) + return true; + + /* + * Dirty and Accessed bits can be set by the CPU. Ignore the Accessed + * bit, as KVM tolerates false negatives/positives, e.g. KVM doesn't + * invalidate TLBs when aging SPTEs, and so it's safe to clobber the + * Accessed bit (and rare in practice). + */ + return is_writable_pte(spte) && !(spte & shadow_dirty_mask); +} + +bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, + const struct kvm_memory_slot *slot, + unsigned int pte_access, gfn_t gfn, kvm_pfn_t pfn, + u64 old_spte, bool prefetch, bool synchronizing, + bool host_writable, u64 *new_spte) +{ + int level = sp->role.level; + u64 spte = SPTE_MMU_PRESENT_MASK; + int is_host_mmio = -1; + bool wrprot = false; + + /* + * For the EPT case, shadow_present_mask has no RWX bits set if + * exec-only page table entries are supported. In that case, + * ACC_USER_MASK and shadow_user_mask are used to represent + * read access. See FNAME(gpte_access) in paging_tmpl.h. + */ + WARN_ON_ONCE((pte_access | shadow_present_mask) == SHADOW_NONPRESENT_VALUE); + + if (sp->role.ad_disabled) + spte |= SPTE_TDP_AD_DISABLED; + else if (kvm_mmu_page_ad_need_write_protect(vcpu->kvm, sp)) + spte |= SPTE_TDP_AD_WRPROT_ONLY; + + spte |= shadow_present_mask; + if (!prefetch || synchronizing) + spte |= shadow_accessed_mask; + + /* + * For simplicity, enforce the NX huge page mitigation even if not + * strictly necessary. KVM could ignore the mitigation if paging is + * disabled in the guest, as the guest doesn't have any page tables to + * abuse. But to safely ignore the mitigation, KVM would have to + * ensure a new MMU is loaded (or all shadow pages zapped) when CR0.PG + * is toggled on, and that's a net negative for performance when TDP is + * enabled. When TDP is disabled, KVM will always switch to a new MMU + * when CR0.PG is toggled, but leveraging that to ignore the mitigation + * would tie make_spte() further to vCPU/MMU state, and add complexity + * just to optimize a mode that is anything but performance critical. + */ + if (level > PG_LEVEL_4K && (pte_access & ACC_EXEC_MASK) && + is_nx_huge_page_enabled(vcpu->kvm)) { + pte_access &= ~ACC_EXEC_MASK; + } + + if (pte_access & ACC_EXEC_MASK) + spte |= shadow_x_mask; + else + spte |= shadow_nx_mask; + + if (pte_access & ACC_USER_MASK) + spte |= shadow_user_mask; + + if (level > PG_LEVEL_4K) + spte |= PT_PAGE_SIZE_MASK; + + if (kvm_x86_ops.get_mt_mask) + spte |= kvm_x86_call(get_mt_mask)(vcpu, gfn, + kvm_is_mmio_pfn(pfn, &is_host_mmio)); + if (host_writable) + spte |= shadow_host_writable_mask; + else + pte_access &= ~ACC_WRITE_MASK; + + if (shadow_me_value && !kvm_is_mmio_pfn(pfn, &is_host_mmio)) + spte |= shadow_me_value; + + spte |= (u64)pfn << PAGE_SHIFT; + + if (pte_access & ACC_WRITE_MASK) { + /* + * Unsync shadow pages that are reachable by the new, writable + * SPTE. Write-protect the SPTE if the page can't be unsync'd, + * e.g. it's write-tracked (upper-level SPs) or has one or more + * shadow pages and unsync'ing pages is not allowed. + * + * When overwriting an existing leaf SPTE, and the old SPTE was + * writable, skip trying to unsync shadow pages as any relevant + * shadow pages must already be unsync, i.e. the hash lookup is + * unnecessary (and expensive). Note, this relies on KVM not + * changing PFNs without first zapping the old SPTE, which is + * guaranteed by both the shadow MMU and the TDP MMU. + */ + if ((!is_last_spte(old_spte, level) || !is_writable_pte(old_spte)) && + mmu_try_to_unsync_pages(vcpu->kvm, slot, gfn, synchronizing, prefetch)) + wrprot = true; + else + spte |= PT_WRITABLE_MASK | shadow_mmu_writable_mask | + shadow_dirty_mask; + } + + if (prefetch && !synchronizing) + spte = mark_spte_for_access_track(spte); + + WARN_ONCE(is_rsvd_spte(&vcpu->arch.mmu->shadow_zero_check, spte, level), + "spte = 0x%llx, level = %d, rsvd bits = 0x%llx", spte, level, + get_rsvd_bits(&vcpu->arch.mmu->shadow_zero_check, spte, level)); + + /* + * Mark the memslot dirty *after* modifying it for access tracking. + * Unlike folios, memslots can be safely marked dirty out of mmu_lock, + * i.e. in the fast page fault handler. + */ + if ((spte & PT_WRITABLE_MASK) && kvm_slot_dirty_track_enabled(slot)) { + /* Enforced by kvm_mmu_hugepage_adjust. */ + WARN_ON_ONCE(level > PG_LEVEL_4K); + mark_page_dirty_in_slot(vcpu->kvm, slot, gfn); + } + + if (cpu_feature_enabled(X86_FEATURE_CLEAR_CPU_BUF_VM_MMIO) && + !kvm_vcpu_can_access_host_mmio(vcpu) && + kvm_is_mmio_pfn(pfn, &is_host_mmio)) + kvm_track_host_mmio_mapping(vcpu); + + *new_spte = spte; + return wrprot; +} + +static u64 modify_spte_protections(u64 spte, u64 set, u64 clear) +{ + bool is_access_track = is_access_track_spte(spte); + + if (is_access_track) + spte = restore_acc_track_spte(spte); + + KVM_MMU_WARN_ON(set & clear); + spte = (spte | set) & ~clear; + + if (is_access_track) + spte = mark_spte_for_access_track(spte); + + return spte; +} + +static u64 make_spte_executable(u64 spte) +{ + return modify_spte_protections(spte, shadow_x_mask, shadow_nx_mask); +} + +static u64 make_spte_nonexecutable(u64 spte) +{ + return modify_spte_protections(spte, shadow_nx_mask, shadow_x_mask); +} + +/* + * Construct an SPTE that maps a sub-page of the given huge page SPTE where + * `index` identifies which sub-page. + * + * This is used during huge page splitting to build the SPTEs that make up the + * new page table. + */ +u64 make_small_spte(struct kvm *kvm, u64 huge_spte, + union kvm_mmu_page_role role, int index) +{ + u64 child_spte = huge_spte; + + KVM_BUG_ON(!is_shadow_present_pte(huge_spte) || !is_large_pte(huge_spte), kvm); + + /* + * The child_spte already has the base address of the huge page being + * split. So we just have to OR in the offset to the page at the next + * lower level for the given index. + */ + child_spte |= (index * KVM_PAGES_PER_HPAGE(role.level)) << PAGE_SHIFT; + + if (role.level == PG_LEVEL_4K) { + child_spte &= ~PT_PAGE_SIZE_MASK; + + /* + * When splitting to a 4K page where execution is allowed, mark + * the page executable as the NX hugepage mitigation no longer + * applies. + */ + if ((role.access & ACC_EXEC_MASK) && is_nx_huge_page_enabled(kvm)) + child_spte = make_spte_executable(child_spte); + } + + return child_spte; +} + +u64 make_huge_spte(struct kvm *kvm, u64 small_spte, int level) +{ + u64 huge_spte; + + KVM_BUG_ON(!is_shadow_present_pte(small_spte) || level == PG_LEVEL_4K, kvm); + + huge_spte = small_spte | PT_PAGE_SIZE_MASK; + + /* + * huge_spte already has the address of the sub-page being collapsed + * from small_spte, so just clear the lower address bits to create the + * huge page address. + */ + huge_spte &= KVM_HPAGE_MASK(level) | ~PAGE_MASK; + + if (is_nx_huge_page_enabled(kvm)) + huge_spte = make_spte_nonexecutable(huge_spte); + + return huge_spte; +} + +u64 make_nonleaf_spte(u64 *child_pt, bool ad_disabled) +{ + u64 spte = SPTE_MMU_PRESENT_MASK; + + spte |= __pa(child_pt) | shadow_present_mask | PT_WRITABLE_MASK | + shadow_user_mask | shadow_x_mask | shadow_me_value; + + if (ad_disabled) + spte |= SPTE_TDP_AD_DISABLED; + else + spte |= shadow_accessed_mask; + + return spte; +} + +u64 mark_spte_for_access_track(u64 spte) +{ + if (spte_ad_enabled(spte)) + return spte & ~shadow_accessed_mask; + + if (is_access_track_spte(spte)) + return spte; + + check_spte_writable_invariants(spte); + + WARN_ONCE(spte & (SHADOW_ACC_TRACK_SAVED_BITS_MASK << + SHADOW_ACC_TRACK_SAVED_BITS_SHIFT), + "Access Tracking saved bit locations are not zero\n"); + + spte |= (spte & SHADOW_ACC_TRACK_SAVED_BITS_MASK) << + SHADOW_ACC_TRACK_SAVED_BITS_SHIFT; + spte &= ~(shadow_acc_track_mask | shadow_accessed_mask); + + return spte; +} + +void kvm_mmu_set_mmio_spte_mask(u64 mmio_value, u64 mmio_mask, u64 access_mask) +{ + BUG_ON((u64)(unsigned)access_mask != access_mask); + WARN_ON(mmio_value & shadow_nonpresent_or_rsvd_lower_gfn_mask); + + /* + * Reset to the original module param value to honor userspace's desire + * to (dis)allow MMIO caching. Update the param itself so that + * userspace can see whether or not KVM is actually using MMIO caching. + */ + enable_mmio_caching = allow_mmio_caching; + if (!enable_mmio_caching) + mmio_value = 0; + + /* + * The mask must contain only bits that are carved out specifically for + * the MMIO SPTE mask, e.g. to ensure there's no overlap with the MMIO + * generation. + */ + if (WARN_ON(mmio_mask & ~SPTE_MMIO_ALLOWED_MASK)) + mmio_value = 0; + + /* + * Disable MMIO caching if the MMIO value collides with the bits that + * are used to hold the relocated GFN when the L1TF mitigation is + * enabled. This should never fire as there is no known hardware that + * can trigger this condition, e.g. SME/SEV CPUs that require a custom + * MMIO value are not susceptible to L1TF. + */ + if (WARN_ON(mmio_value & (shadow_nonpresent_or_rsvd_mask << + SHADOW_NONPRESENT_OR_RSVD_MASK_LEN))) + mmio_value = 0; + + /* + * The masked MMIO value must obviously match itself and a frozen SPTE + * must not get a false positive. Frozen SPTEs and MMIO SPTEs should + * never collide as MMIO must set some RWX bits, and frozen SPTEs must + * not set any RWX bits. + */ + if (WARN_ON((mmio_value & mmio_mask) != mmio_value) || + WARN_ON(mmio_value && (FROZEN_SPTE & mmio_mask) == mmio_value)) + mmio_value = 0; + + if (!mmio_value) + enable_mmio_caching = false; + + shadow_mmio_value = mmio_value; + shadow_mmio_mask = mmio_mask; + shadow_mmio_access_mask = access_mask; +} +EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_mmu_set_mmio_spte_mask); + +void kvm_mmu_set_mmio_spte_value(struct kvm *kvm, u64 mmio_value) +{ + kvm->arch.shadow_mmio_value = mmio_value; +} +EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_mmu_set_mmio_spte_value); + +void kvm_mmu_set_me_spte_mask(u64 me_value, u64 me_mask) +{ + /* shadow_me_value must be a subset of shadow_me_mask */ + if (WARN_ON(me_value & ~me_mask)) + me_value = me_mask = 0; + + shadow_me_value = me_value; + shadow_me_mask = me_mask; +} +EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_mmu_set_me_spte_mask); + +void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only) +{ + kvm_ad_enabled = has_ad_bits; + + shadow_user_mask = VMX_EPT_READABLE_MASK; + shadow_accessed_mask = VMX_EPT_ACCESS_BIT; + shadow_dirty_mask = VMX_EPT_DIRTY_BIT; + shadow_nx_mask = 0ull; + shadow_x_mask = VMX_EPT_EXECUTABLE_MASK; + /* VMX_EPT_SUPPRESS_VE_BIT is needed for W or X violation. */ + shadow_present_mask = + (has_exec_only ? 0ull : VMX_EPT_READABLE_MASK) | VMX_EPT_SUPPRESS_VE_BIT; + + shadow_acc_track_mask = VMX_EPT_RWX_MASK; + shadow_host_writable_mask = EPT_SPTE_HOST_WRITABLE; + shadow_mmu_writable_mask = EPT_SPTE_MMU_WRITABLE; + + /* + * EPT Misconfigurations are generated if the value of bits 2:0 + * of an EPT paging-structure entry is 110b (write/execute). + */ + kvm_mmu_set_mmio_spte_mask(VMX_EPT_MISCONFIG_WX_VALUE, + VMX_EPT_RWX_MASK | VMX_EPT_SUPPRESS_VE_BIT, 0); +} +EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_mmu_set_ept_masks); + +void kvm_mmu_reset_all_pte_masks(void) +{ + u8 low_phys_bits; + u64 mask; + + kvm_ad_enabled = true; + + /* + * If the CPU has 46 or less physical address bits, then set an + * appropriate mask to guard against L1TF attacks. Otherwise, it is + * assumed that the CPU is not vulnerable to L1TF. + * + * Some Intel CPUs address the L1 cache using more PA bits than are + * reported by CPUID. Use the PA width of the L1 cache when possible + * to achieve more effective mitigation, e.g. if system RAM overlaps + * the most significant bits of legal physical address space. + */ + shadow_nonpresent_or_rsvd_mask = 0; + low_phys_bits = boot_cpu_data.x86_phys_bits; + if (boot_cpu_has_bug(X86_BUG_L1TF) && + !WARN_ON_ONCE(boot_cpu_data.x86_cache_bits >= + 52 - SHADOW_NONPRESENT_OR_RSVD_MASK_LEN)) { + low_phys_bits = boot_cpu_data.x86_cache_bits + - SHADOW_NONPRESENT_OR_RSVD_MASK_LEN; + shadow_nonpresent_or_rsvd_mask = + rsvd_bits(low_phys_bits, boot_cpu_data.x86_cache_bits - 1); + } + + shadow_nonpresent_or_rsvd_lower_gfn_mask = + GENMASK_ULL(low_phys_bits - 1, PAGE_SHIFT); + + shadow_user_mask = PT_USER_MASK; + shadow_accessed_mask = PT_ACCESSED_MASK; + shadow_dirty_mask = PT_DIRTY_MASK; + shadow_nx_mask = PT64_NX_MASK; + shadow_x_mask = 0; + shadow_present_mask = PT_PRESENT_MASK; + + shadow_acc_track_mask = 0; + shadow_me_mask = 0; + shadow_me_value = 0; + + shadow_host_writable_mask = DEFAULT_SPTE_HOST_WRITABLE; + shadow_mmu_writable_mask = DEFAULT_SPTE_MMU_WRITABLE; + + /* + * Set a reserved PA bit in MMIO SPTEs to generate page faults with + * PFEC.RSVD=1 on MMIO accesses. 64-bit PTEs (PAE, x86-64, and EPT + * paging) support a maximum of 52 bits of PA, i.e. if the CPU supports + * 52-bit physical addresses then there are no reserved PA bits in the + * PTEs and so the reserved PA approach must be disabled. + */ + if (kvm_host.maxphyaddr < 52) + mask = BIT_ULL(51) | PT_PRESENT_MASK; + else + mask = 0; + + kvm_mmu_set_mmio_spte_mask(mask, mask, ACC_WRITE_MASK | ACC_USER_MASK); +} |