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| author | Paolo Bonzini <pbonzini@redhat.com> | 2024-07-17 13:04:48 -0400 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2024-07-26 14:46:14 -0400 |
| commit | 5932ca411e533e7ad2b97c47b4357a05fa06c2a5 (patch) | |
| tree | 7a164c01d4fb3b3f840d9b464d7685c9ba109a76 /arch/x86/kvm | |
| parent | c2adcf051be01d3da1e138c178a680514299461b (diff) | |
| download | linux-stable-5932ca411e533e7ad2b97c47b4357a05fa06c2a5.tar.gz linux-stable-5932ca411e533e7ad2b97c47b4357a05fa06c2a5.tar.bz2 linux-stable-5932ca411e533e7ad2b97c47b4357a05fa06c2a5.zip | |
KVM: x86: disallow pre-fault for SNP VMs before initialization
KVM_PRE_FAULT_MEMORY for an SNP guest can race with
sev_gmem_post_populate() in bad ways. The following sequence for
instance can potentially trigger an RMP fault:
thread A, sev_gmem_post_populate: called
thread B, sev_gmem_prepare: places below 'pfn' in a private state in RMP
thread A, sev_gmem_post_populate: *vaddr = kmap_local_pfn(pfn + i);
thread A, sev_gmem_post_populate: copy_from_user(vaddr, src + i * PAGE_SIZE, PAGE_SIZE);
RMP #PF
Fix this by only allowing KVM_PRE_FAULT_MEMORY to run after a guest's
initial private memory contents have been finalized via
KVM_SEV_SNP_LAUNCH_FINISH.
Beyond fixing this issue, it just sort of makes sense to enforce this,
since the KVM_PRE_FAULT_MEMORY documentation states:
"KVM maps memory as if the vCPU generated a stage-2 read page fault"
which sort of implies we should be acting on the same guest state that a
vCPU would see post-launch after the initial guest memory is all set up.
Co-developed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kvm')
| -rw-r--r-- | arch/x86/kvm/mmu/mmu.c | 3 | ||||
| -rw-r--r-- | arch/x86/kvm/svm/sev.c | 8 | ||||
| -rw-r--r-- | arch/x86/kvm/svm/svm.c | 1 | ||||
| -rw-r--r-- | arch/x86/kvm/x86.c | 3 |
4 files changed, 15 insertions, 0 deletions
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 901be9e420a4..26ef5b6ac3c1 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -4743,6 +4743,9 @@ long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu, u64 end; int r; + if (!vcpu->kvm->arch.pre_fault_allowed) + return -EOPNOTSUPP; + /* * reload is efficient when called repeatedly, so we can do it on * every iteration. diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index a16c873b3232..6589091e8ce0 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -2549,6 +2549,14 @@ static int snp_launch_finish(struct kvm *kvm, struct kvm_sev_cmd *argp) data->gctx_paddr = __psp_pa(sev->snp_context); ret = sev_issue_cmd(kvm, SEV_CMD_SNP_LAUNCH_FINISH, data, &argp->error); + /* + * Now that there will be no more SNP_LAUNCH_UPDATE ioctls, private pages + * can be given to the guest simply by marking the RMP entry as private. + * This can happen on first access and also with KVM_PRE_FAULT_MEMORY. + */ + if (!ret) + kvm->arch.pre_fault_allowed = true; + kfree(id_auth); e_free_id_block: diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index c115d26844f7..d6f252555ab3 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -4949,6 +4949,7 @@ static int svm_vm_init(struct kvm *kvm) to_kvm_sev_info(kvm)->need_init = true; kvm->arch.has_private_mem = (type == KVM_X86_SNP_VM); + kvm->arch.pre_fault_allowed = !kvm->arch.has_private_mem; } if (!pause_filter_count || !pause_filter_thresh) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index af6c8cf6a37a..52778689cef4 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -12646,6 +12646,9 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) kvm->arch.vm_type = type; kvm->arch.has_private_mem = (type == KVM_X86_SW_PROTECTED_VM); + /* Decided by the vendor code for other VM types. */ + kvm->arch.pre_fault_allowed = + type == KVM_X86_DEFAULT_VM || type == KVM_X86_SW_PROTECTED_VM; ret = kvm_page_track_init(kvm); if (ret) |