From 86931ff7207bc045fa5439ef97b31859613dc303 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Thu, 28 Apr 2022 23:34:16 +0000 Subject: [PATCH 1/3] KVM: x86/mmu: Do not create SPTEs for GFNs that exceed host.MAXPHYADDR Disallow memslots and MMIO SPTEs whose gpa range would exceed the host's MAXPHYADDR, i.e. don't create SPTEs for gfns that exceed host.MAXPHYADDR. The TDP MMU bounds its zapping based on host.MAXPHYADDR, and so if the guest, possibly with help from userspace, manages to coerce KVM into creating a SPTE for an "impossible" gfn, KVM will leak the associated shadow pages (page tables): WARNING: CPU: 10 PID: 1122 at arch/x86/kvm/mmu/tdp_mmu.c:57 kvm_mmu_uninit_tdp_mmu+0x4b/0x60 [kvm] Modules linked in: kvm_intel kvm irqbypass CPU: 10 PID: 1122 Comm: set_memory_regi Tainted: G W 5.18.0-rc1+ #293 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:kvm_mmu_uninit_tdp_mmu+0x4b/0x60 [kvm] Call Trace: kvm_arch_destroy_vm+0x130/0x1b0 [kvm] kvm_destroy_vm+0x162/0x2d0 [kvm] kvm_vm_release+0x1d/0x30 [kvm] __fput+0x82/0x240 task_work_run+0x5b/0x90 exit_to_user_mode_prepare+0xd2/0xe0 syscall_exit_to_user_mode+0x1d/0x40 entry_SYSCALL_64_after_hwframe+0x44/0xae On bare metal, encountering an impossible gpa in the page fault path is well and truly impossible, barring CPU bugs, as the CPU will signal #PF during the gva=>gpa translation (or a similar failure when stuffing a physical address into e.g. the VMCS/VMCB). But if KVM is running as a VM itself, the MAXPHYADDR enumerated to KVM may not be the actual MAXPHYADDR of the underlying hardware, in which case the hardware will not fault on the illegal-from-KVM's-perspective gpa. Alternatively, KVM could continue allowing the dodgy behavior and simply zap the max possible range. But, for hosts with MAXPHYADDR < 52, that's a (minor) waste of cycles, and more importantly, KVM can't reasonably support impossible memslots when running on bare metal (or with an accurate MAXPHYADDR as a VM). Note, limiting the overhead by checking if KVM is running as a guest is not a safe option as the host isn't required to announce itself to the guest in any way, e.g. doesn't need to set the HYPERVISOR CPUID bit. A second alternative to disallowing the memslot behavior would be to disallow creating a VM with guest.MAXPHYADDR > host.MAXPHYADDR. That restriction is undesirable as there are legitimate use cases for doing so, e.g. using the highest host.MAXPHYADDR out of a pool of heterogeneous systems so that VMs can be migrated between hosts with different MAXPHYADDRs without running afoul of the allow_smaller_maxphyaddr mess. Note that any guest.MAXPHYADDR is valid with shadow paging, and it is even useful in order to test KVM with MAXPHYADDR=52 (i.e. without any reserved physical address bits). The now common kvm_mmu_max_gfn() is inclusive instead of exclusive. The memslot and TDP MMU code want an exclusive value, but the name implies the returned value is inclusive, and the MMIO path needs an inclusive check. Fixes: faaf05b00aec ("kvm: x86/mmu: Support zapping SPTEs in the TDP MMU") Fixes: 524a1e4e381f ("KVM: x86/mmu: Don't leak non-leaf SPTEs when zapping all SPTEs") Cc: stable@vger.kernel.org Cc: Maxim Levitsky Cc: Ben Gardon Cc: David Matlack Signed-off-by: Sean Christopherson Message-Id: <20220428233416.2446833-1-seanjc@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/mmu.h | 24 ++++++++++++++++++++++++ arch/x86/kvm/mmu/mmu.c | 10 ++++++++-- arch/x86/kvm/mmu/spte.h | 6 ------ arch/x86/kvm/mmu/tdp_mmu.c | 15 ++++++++------- arch/x86/kvm/x86.c | 6 +++++- 5 files changed, 45 insertions(+), 16 deletions(-) diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h index e6cae6f22683..a335e7f1f69e 100644 --- a/arch/x86/kvm/mmu.h +++ b/arch/x86/kvm/mmu.h @@ -65,6 +65,30 @@ static __always_inline u64 rsvd_bits(int s, int e) return ((2ULL << (e - s)) - 1) << s; } +/* + * The number of non-reserved physical address bits irrespective of features + * that repurpose legal bits, e.g. MKTME. + */ +extern u8 __read_mostly shadow_phys_bits; + +static inline gfn_t kvm_mmu_max_gfn(void) +{ + /* + * Note that this uses the host MAXPHYADDR, not the guest's. + * EPT/NPT cannot support GPAs that would exceed host.MAXPHYADDR; + * assuming KVM is running on bare metal, guest accesses beyond + * host.MAXPHYADDR will hit a #PF(RSVD) and never cause a vmexit + * (either EPT Violation/Misconfig or #NPF), and so KVM will never + * install a SPTE for such addresses. If KVM is running as a VM + * itself, on the other hand, it might see a MAXPHYADDR that is less + * than hardware's real MAXPHYADDR. Using the host MAXPHYADDR + * disallows such SPTEs entirely and simplifies the TDP MMU. + */ + int max_gpa_bits = likely(tdp_enabled) ? shadow_phys_bits : 52; + + return (1ULL << (max_gpa_bits - PAGE_SHIFT)) - 1; +} + void kvm_mmu_set_mmio_spte_mask(u64 mmio_value, u64 mmio_mask, u64 access_mask); void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only); diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index f9080ee50ffa..5f6225c384e6 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -2992,9 +2992,15 @@ static bool handle_abnormal_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fa /* * If MMIO caching is disabled, emulate immediately without * touching the shadow page tables as attempting to install an - * MMIO SPTE will just be an expensive nop. + * MMIO SPTE will just be an expensive nop. Do not cache MMIO + * whose gfn is greater than host.MAXPHYADDR, any guest that + * generates such gfns is running nested and is being tricked + * by L0 userspace (you can observe gfn > L1.MAXPHYADDR if + * and only if L1's MAXPHYADDR is inaccurate with respect to + * the hardware's). */ - if (unlikely(!shadow_mmio_value)) { + if (unlikely(!shadow_mmio_value) || + unlikely(fault->gfn > kvm_mmu_max_gfn())) { *ret_val = RET_PF_EMULATE; return true; } diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h index 73f12615416f..e4abeb5df1b1 100644 --- a/arch/x86/kvm/mmu/spte.h +++ b/arch/x86/kvm/mmu/spte.h @@ -201,12 +201,6 @@ static inline bool is_removed_spte(u64 spte) */ extern u64 __read_mostly shadow_nonpresent_or_rsvd_lower_gfn_mask; -/* - * The number of non-reserved physical address bits irrespective of features - * that repurpose legal bits, e.g. MKTME. - */ -extern u8 __read_mostly shadow_phys_bits; - static inline bool is_mmio_spte(u64 spte) { return (spte & shadow_mmio_mask) == shadow_mmio_value && diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index c472769e0300..edc68538819b 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -815,14 +815,15 @@ static inline bool __must_check tdp_mmu_iter_cond_resched(struct kvm *kvm, return iter->yielded; } -static inline gfn_t tdp_mmu_max_gfn_host(void) +static inline gfn_t tdp_mmu_max_gfn_exclusive(void) { /* - * Bound TDP MMU walks at host.MAXPHYADDR, guest accesses beyond that - * will hit a #PF(RSVD) and never hit an EPT Violation/Misconfig / #NPF, - * and so KVM will never install a SPTE for such addresses. + * Bound TDP MMU walks at host.MAXPHYADDR. KVM disallows memslots with + * a gpa range that would exceed the max gfn, and KVM does not create + * MMIO SPTEs for "impossible" gfns, instead sending such accesses down + * the slow emulation path every time. */ - return 1ULL << (shadow_phys_bits - PAGE_SHIFT); + return kvm_mmu_max_gfn() + 1; } static void __tdp_mmu_zap_root(struct kvm *kvm, struct kvm_mmu_page *root, @@ -830,7 +831,7 @@ static void __tdp_mmu_zap_root(struct kvm *kvm, struct kvm_mmu_page *root, { struct tdp_iter iter; - gfn_t end = tdp_mmu_max_gfn_host(); + gfn_t end = tdp_mmu_max_gfn_exclusive(); gfn_t start = 0; for_each_tdp_pte_min_level(iter, root, zap_level, start, end) { @@ -923,7 +924,7 @@ static bool tdp_mmu_zap_leafs(struct kvm *kvm, struct kvm_mmu_page *root, { struct tdp_iter iter; - end = min(end, tdp_mmu_max_gfn_host()); + end = min(end, tdp_mmu_max_gfn_exclusive()); lockdep_assert_held_write(&kvm->mmu_lock); diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 547ba00ef64f..43174a8d9497 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11995,8 +11995,12 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, struct kvm_memory_slot *new, enum kvm_mr_change change) { - if (change == KVM_MR_CREATE || change == KVM_MR_MOVE) + if (change == KVM_MR_CREATE || change == KVM_MR_MOVE) { + if ((new->base_gfn + new->npages - 1) > kvm_mmu_max_gfn()) + return -EINVAL; + return kvm_alloc_memslot_metadata(kvm, new); + } if (change == KVM_MR_FLAGS_ONLY) memcpy(&new->arch, &old->arch, sizeof(old->arch)); From d495f942f40aa412f8d4d65951152648cfa09903 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Fri, 22 Apr 2022 12:30:13 +0200 Subject: [PATCH 2/3] KVM: fix bad user ABI for KVM_EXIT_SYSTEM_EVENT When KVM_EXIT_SYSTEM_EVENT was introduced, it included a flags member that at the time was unused. Unfortunately this extensibility mechanism has several issues: - x86 is not writing the member, so it would not be possible to use it on x86 except for new events - the member is not aligned to 64 bits, so the definition of the uAPI struct is incorrect for 32- on 64-bit userspace. This is a problem for RISC-V, which supports CONFIG_KVM_COMPAT, but fortunately usage of flags was only introduced in 5.18. Since padding has to be introduced, place a new field in there that tells if the flags field is valid. To allow further extensibility, in fact, change flags to an array of 16 values, and store how many of the values are valid. The availability of the new ndata field is tied to a system capability; all architectures are changed to fill in the field. To avoid breaking compilation of userspace that was using the flags field, provide a userspace-only union to overlap flags with data[0]. The new field is placed at the same offset for both 32- and 64-bit userspace. Cc: Will Deacon Cc: Marc Zyngier Cc: Peter Gonda Cc: Sean Christopherson Signed-off-by: Paolo Bonzini Reported-by: kernel test robot Message-Id: <20220422103013.34832-1-pbonzini@redhat.com> Signed-off-by: Paolo Bonzini --- Documentation/virt/kvm/api.rst | 24 +++++++++++++++++------- arch/arm64/kvm/psci.c | 3 ++- arch/riscv/kvm/vcpu_sbi.c | 5 +++-- arch/x86/kvm/x86.c | 2 ++ include/uapi/linux/kvm.h | 10 +++++++++- virt/kvm/kvm_main.c | 1 + 6 files changed, 34 insertions(+), 11 deletions(-) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 85c7abc51af5..4a900cdbc62e 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -5986,16 +5986,16 @@ should put the acknowledged interrupt vector into the 'epr' field. #define KVM_SYSTEM_EVENT_RESET 2 #define KVM_SYSTEM_EVENT_CRASH 3 __u32 type; - __u64 flags; + __u32 ndata; + __u64 data[16]; } system_event; If exit_reason is KVM_EXIT_SYSTEM_EVENT then the vcpu has triggered a system-level event using some architecture specific mechanism (hypercall or some special instruction). In case of ARM64, this is triggered using -HVC instruction based PSCI call from the vcpu. The 'type' field describes -the system-level event type. The 'flags' field describes architecture -specific flags for the system-level event. +HVC instruction based PSCI call from the vcpu. +The 'type' field describes the system-level event type. Valid values for 'type' are: - KVM_SYSTEM_EVENT_SHUTDOWN -- the guest has requested a shutdown of the @@ -6010,10 +6010,20 @@ Valid values for 'type' are: to ignore the request, or to gather VM memory core dump and/or reset/shutdown of the VM. -Valid flags are: +If KVM_CAP_SYSTEM_EVENT_DATA is present, the 'data' field can contain +architecture specific information for the system-level event. Only +the first `ndata` items (possibly zero) of the data array are valid. - - KVM_SYSTEM_EVENT_RESET_FLAG_PSCI_RESET2 (arm64 only) -- the guest issued - a SYSTEM_RESET2 call according to v1.1 of the PSCI specification. + - for arm64, data[0] is set to KVM_SYSTEM_EVENT_RESET_FLAG_PSCI_RESET2 if + the guest issued a SYSTEM_RESET2 call according to v1.1 of the PSCI + specification. + + - for RISC-V, data[0] is set to the value of the second argument of the + ``sbi_system_reset`` call. + +Previous versions of Linux defined a `flags` member in this struct. The +field is now aliased to `data[0]`. Userspace can assume that it is only +written if ndata is greater than 0. :: diff --git a/arch/arm64/kvm/psci.c b/arch/arm64/kvm/psci.c index baac2b405f23..708d80e8e60d 100644 --- a/arch/arm64/kvm/psci.c +++ b/arch/arm64/kvm/psci.c @@ -181,7 +181,8 @@ static void kvm_prepare_system_event(struct kvm_vcpu *vcpu, u32 type, u64 flags) memset(&vcpu->run->system_event, 0, sizeof(vcpu->run->system_event)); vcpu->run->system_event.type = type; - vcpu->run->system_event.flags = flags; + vcpu->run->system_event.ndata = 1; + vcpu->run->system_event.data[0] = flags; vcpu->run->exit_reason = KVM_EXIT_SYSTEM_EVENT; } diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c index a09ecb97b890..d45e7da3f0d3 100644 --- a/arch/riscv/kvm/vcpu_sbi.c +++ b/arch/riscv/kvm/vcpu_sbi.c @@ -83,7 +83,7 @@ void kvm_riscv_vcpu_sbi_forward(struct kvm_vcpu *vcpu, struct kvm_run *run) void kvm_riscv_vcpu_sbi_system_reset(struct kvm_vcpu *vcpu, struct kvm_run *run, - u32 type, u64 flags) + u32 type, u64 reason) { unsigned long i; struct kvm_vcpu *tmp; @@ -94,7 +94,8 @@ void kvm_riscv_vcpu_sbi_system_reset(struct kvm_vcpu *vcpu, memset(&run->system_event, 0, sizeof(run->system_event)); run->system_event.type = type; - run->system_event.flags = flags; + run->system_event.ndata = 1; + run->system_event.data[0] = reason; run->exit_reason = KVM_EXIT_SYSTEM_EVENT; } diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 43174a8d9497..07d789b1d366 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -10015,12 +10015,14 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) if (kvm_check_request(KVM_REQ_HV_CRASH, vcpu)) { vcpu->run->exit_reason = KVM_EXIT_SYSTEM_EVENT; vcpu->run->system_event.type = KVM_SYSTEM_EVENT_CRASH; + vcpu->run->system_event.ndata = 0; r = 0; goto out; } if (kvm_check_request(KVM_REQ_HV_RESET, vcpu)) { vcpu->run->exit_reason = KVM_EXIT_SYSTEM_EVENT; vcpu->run->system_event.type = KVM_SYSTEM_EVENT_RESET; + vcpu->run->system_event.ndata = 0; r = 0; goto out; } diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 91a6fe4e02c0..6a184d260c7f 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -445,7 +445,13 @@ struct kvm_run { #define KVM_SYSTEM_EVENT_RESET 2 #define KVM_SYSTEM_EVENT_CRASH 3 __u32 type; - __u64 flags; + __u32 ndata; + union { +#ifndef __KERNEL__ + __u64 flags; +#endif + __u64 data[16]; + }; } system_event; /* KVM_EXIT_S390_STSI */ struct { @@ -1144,6 +1150,8 @@ struct kvm_ppc_resize_hpt { #define KVM_CAP_S390_MEM_OP_EXTENSION 211 #define KVM_CAP_PMU_CAPABILITY 212 #define KVM_CAP_DISABLE_QUIRKS2 213 +/* #define KVM_CAP_VM_TSC_CONTROL 214 */ +#define KVM_CAP_SYSTEM_EVENT_DATA 215 #ifdef KVM_CAP_IRQ_ROUTING diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index dfb7dabdbc63..ac57fc2c935f 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -4333,6 +4333,7 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg) return 0; #endif case KVM_CAP_BINARY_STATS_FD: + case KVM_CAP_SYSTEM_EVENT_DATA: return 1; default: break; From 44187235cbcc7c1129ea7c004bc12f8757d29415 Mon Sep 17 00:00:00 2001 From: Mingwei Zhang Date: Fri, 29 Apr 2022 03:17:57 +0000 Subject: [PATCH 3/3] KVM: x86/mmu: fix potential races when walking host page table KVM uses lookup_address_in_mm() to detect the hugepage size that the host uses to map a pfn. The function suffers from several issues: - no usage of READ_ONCE(*). This allows multiple dereference of the same page table entry. The TOCTOU problem because of that may cause KVM to incorrectly treat a newly generated leaf entry as a nonleaf one, and dereference the content by using its pfn value. - the information returned does not match what KVM needs; for non-present entries it returns the level at which the walk was terminated, as long as the entry is not 'none'. KVM needs level information of only 'present' entries, otherwise it may regard a non-present PXE entry as a present large page mapping. - the function is not safe for mappings that can be torn down, because it does not disable IRQs and because it returns a PTE pointer which is never safe to dereference after the function returns. So implement the logic for walking host page tables directly in KVM, and stop using lookup_address_in_mm(). Cc: Sean Christopherson Cc: Paolo Bonzini Signed-off-by: Mingwei Zhang Message-Id: <20220429031757.2042406-1-mizhang@google.com> [Inline in host_pfn_mapping_level, ensure no semantic change for its callers. - Paolo] Signed-off-by: Paolo Bonzini --- arch/x86/kvm/mmu/mmu.c | 47 +++++++++++++++++++++++++++++++++++++----- 1 file changed, 42 insertions(+), 5 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 5f6225c384e6..64a2a7e2be90 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -2804,8 +2804,12 @@ static int host_pfn_mapping_level(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn, const struct kvm_memory_slot *slot) { unsigned long hva; - pte_t *pte; - int level; + unsigned long flags; + int level = PG_LEVEL_4K; + pgd_t pgd; + p4d_t p4d; + pud_t pud; + pmd_t pmd; if (!PageCompound(pfn_to_page(pfn)) && !kvm_is_zone_device_pfn(pfn)) return PG_LEVEL_4K; @@ -2820,10 +2824,43 @@ static int host_pfn_mapping_level(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn, */ hva = __gfn_to_hva_memslot(slot, gfn); - pte = lookup_address_in_mm(kvm->mm, hva, &level); - if (unlikely(!pte)) - return PG_LEVEL_4K; + /* + * Lookup the mapping level in the current mm. The information + * may become stale soon, but it is safe to use as long as + * 1) mmu_notifier_retry was checked after taking mmu_lock, and + * 2) mmu_lock is taken now. + * + * We still need to disable IRQs to prevent concurrent tear down + * of page tables. + */ + local_irq_save(flags); + pgd = READ_ONCE(*pgd_offset(kvm->mm, hva)); + if (pgd_none(pgd)) + goto out; + + p4d = READ_ONCE(*p4d_offset(&pgd, hva)); + if (p4d_none(p4d) || !p4d_present(p4d)) + goto out; + + pud = READ_ONCE(*pud_offset(&p4d, hva)); + if (pud_none(pud) || !pud_present(pud)) + goto out; + + if (pud_large(pud)) { + level = PG_LEVEL_1G; + goto out; + } + + pmd = READ_ONCE(*pmd_offset(&pud, hva)); + if (pmd_none(pmd) || !pmd_present(pmd)) + goto out; + + if (pmd_large(pmd)) + level = PG_LEVEL_2M; + +out: + local_irq_restore(flags); return level; }