From: Tom Lendacky Date: Thu, 20 Mar 2025 13:26:49 +0000 (-0500) Subject: KVM: SVM: Decrypt SEV VMSA in dump_vmcb() if debugging is enabled X-Git-Tag: v6.16-rc1~78^2~4^2~14 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=962e2b6152ef1264224a9e1793ad2d5b5f3311a8;p=thirdparty%2Flinux.git KVM: SVM: Decrypt SEV VMSA in dump_vmcb() if debugging is enabled An SEV-ES/SEV-SNP VM save area (VMSA) can be decrypted if the guest policy allows debugging. Update the dump_vmcb() routine to output some of the SEV VMSA contents if possible. This can be useful for debug purposes. Signed-off-by: Tom Lendacky Acked-by: Borislav Petkov (AMD) Tested-by: Kim Phillips Link: https://lore.kernel.org/r/ea3b852c295b6f4b200925ed6b6e2c90d9475e71.1742477213.git.thomas.lendacky@amd.com Signed-off-by: Sean Christopherson --- diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index 7d11e82e4fa41..11695362b6b2a 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -560,6 +560,8 @@ static int sev_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp) if (copy_from_user(¶ms, u64_to_user_ptr(argp->data), sizeof(params))) return -EFAULT; + sev->policy = params.policy; + memset(&start, 0, sizeof(start)); dh_blob = NULL; @@ -2199,6 +2201,8 @@ static int snp_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp) if (params.policy & SNP_POLICY_MASK_SINGLE_SOCKET) return -EINVAL; + sev->policy = params.policy; + sev->snp_context = snp_context_create(kvm, argp); if (!sev->snp_context) return -ENOTTY; @@ -4922,3 +4926,97 @@ int sev_private_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn) return level; } + +struct vmcb_save_area *sev_decrypt_vmsa(struct kvm_vcpu *vcpu) +{ + struct vcpu_svm *svm = to_svm(vcpu); + struct vmcb_save_area *vmsa; + struct kvm_sev_info *sev; + int error = 0; + int ret; + + if (!sev_es_guest(vcpu->kvm)) + return NULL; + + /* + * If the VMSA has not yet been encrypted, return a pointer to the + * current un-encrypted VMSA. + */ + if (!vcpu->arch.guest_state_protected) + return (struct vmcb_save_area *)svm->sev_es.vmsa; + + sev = to_kvm_sev_info(vcpu->kvm); + + /* Check if the SEV policy allows debugging */ + if (sev_snp_guest(vcpu->kvm)) { + if (!(sev->policy & SNP_POLICY_DEBUG)) + return NULL; + } else { + if (sev->policy & SEV_POLICY_NODBG) + return NULL; + } + + if (sev_snp_guest(vcpu->kvm)) { + struct sev_data_snp_dbg dbg = {0}; + + vmsa = snp_alloc_firmware_page(__GFP_ZERO); + if (!vmsa) + return NULL; + + dbg.gctx_paddr = __psp_pa(sev->snp_context); + dbg.src_addr = svm->vmcb->control.vmsa_pa; + dbg.dst_addr = __psp_pa(vmsa); + + ret = sev_do_cmd(SEV_CMD_SNP_DBG_DECRYPT, &dbg, &error); + + /* + * Return the target page to a hypervisor page no matter what. + * If this fails, the page can't be used, so leak it and don't + * try to use it. + */ + if (snp_page_reclaim(vcpu->kvm, PHYS_PFN(__pa(vmsa)))) + return NULL; + + if (ret) { + pr_err("SEV: SNP_DBG_DECRYPT failed ret=%d, fw_error=%d (%#x)\n", + ret, error, error); + free_page((unsigned long)vmsa); + + return NULL; + } + } else { + struct sev_data_dbg dbg = {0}; + struct page *vmsa_page; + + vmsa_page = alloc_page(GFP_KERNEL); + if (!vmsa_page) + return NULL; + + vmsa = page_address(vmsa_page); + + dbg.handle = sev->handle; + dbg.src_addr = svm->vmcb->control.vmsa_pa; + dbg.dst_addr = __psp_pa(vmsa); + dbg.len = PAGE_SIZE; + + ret = sev_do_cmd(SEV_CMD_DBG_DECRYPT, &dbg, &error); + if (ret) { + pr_err("SEV: SEV_CMD_DBG_DECRYPT failed ret=%d, fw_error=%d (0x%x)\n", + ret, error, error); + __free_page(vmsa_page); + + return NULL; + } + } + + return vmsa; +} + +void sev_free_decrypted_vmsa(struct kvm_vcpu *vcpu, struct vmcb_save_area *vmsa) +{ + /* If the VMSA has not yet been encrypted, nothing was allocated */ + if (!vcpu->arch.guest_state_protected || !vmsa) + return; + + free_page((unsigned long)vmsa); +} diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index cc1c721ba067d..36e2199fe4838 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -3442,6 +3442,15 @@ static void dump_vmcb(struct kvm_vcpu *vcpu) pr_err("%-20s%016llx\n", "avic_logical_id:", control->avic_logical_id); pr_err("%-20s%016llx\n", "avic_physical_id:", control->avic_physical_id); pr_err("%-20s%016llx\n", "vmsa_pa:", control->vmsa_pa); + + if (sev_es_guest(vcpu->kvm)) { + save = sev_decrypt_vmsa(vcpu); + if (!save) + goto no_vmsa; + + save01 = save; + } + pr_err("VMCB State Save Area:\n"); pr_err("%-5s s: %04x a: %04x l: %08x b: %016llx\n", "es:", @@ -3512,6 +3521,10 @@ static void dump_vmcb(struct kvm_vcpu *vcpu) pr_err("%-15s %016llx %-13s %016llx\n", "excp_from:", save->last_excp_from, "excp_to:", save->last_excp_to); + +no_vmsa: + if (sev_es_guest(vcpu->kvm)) + sev_free_decrypted_vmsa(vcpu, save); } static bool svm_check_exit_valid(u64 exit_code) diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h index d4490eaed55dd..5ce34a1faf6ac 100644 --- a/arch/x86/kvm/svm/svm.h +++ b/arch/x86/kvm/svm/svm.h @@ -98,6 +98,7 @@ struct kvm_sev_info { unsigned int asid; /* ASID used for this guest */ unsigned int handle; /* SEV firmware handle */ int fd; /* SEV device fd */ + unsigned long policy; unsigned long pages_locked; /* Number of pages locked */ struct list_head regions_list; /* List of registered regions */ u64 ap_jump_table; /* SEV-ES AP Jump Table address */ @@ -114,6 +115,9 @@ struct kvm_sev_info { struct mutex guest_req_mutex; /* Must acquire before using bounce buffers */ }; +#define SEV_POLICY_NODBG BIT_ULL(0) +#define SNP_POLICY_DEBUG BIT_ULL(19) + struct kvm_svm { struct kvm kvm; @@ -783,6 +787,8 @@ void sev_snp_init_protected_guest_state(struct kvm_vcpu *vcpu); int sev_gmem_prepare(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, int max_order); void sev_gmem_invalidate(kvm_pfn_t start, kvm_pfn_t end); int sev_private_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn); +struct vmcb_save_area *sev_decrypt_vmsa(struct kvm_vcpu *vcpu); +void sev_free_decrypted_vmsa(struct kvm_vcpu *vcpu, struct vmcb_save_area *vmsa); #else static inline struct page *snp_safe_alloc_page_node(int node, gfp_t gfp) { @@ -814,6 +820,11 @@ static inline int sev_private_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn) return 0; } +static inline struct vmcb_save_area *sev_decrypt_vmsa(struct kvm_vcpu *vcpu) +{ + return NULL; +} +static inline void sev_free_decrypted_vmsa(struct kvm_vcpu *vcpu, struct vmcb_save_area *vmsa) {} #endif /* vmenter.S */