KVM: SEV: remove ghcb variable declarations

To avoid possible time-of-check/time-of-use issues, the GHCB should
almost never be accessed outside dump_ghcb, sev_es_sync_to_ghcb
and sev_es_sync_from_ghcb.  The only legitimate uses are to set the
exitinfo fields and to find the address of the scratch area embedded
in the ghcb.  Accessing ghcb_usage also goes through svm->sev_es.ghcb
in sev_es_validate_vmgexit(), but that is because anyway the value is
not used.

Removing a shortcut variable that contains the value of svm->sev_es.ghcb
makes these cases a bit more verbose, but it limits the chance of someone
reading the ghcb by mistake.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index ca4ba5f..d3aec1f 100644 (file)
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2454,12 +2454,9 @@ static int sev_es_validate_vmgexit(struct vcpu_svm *svm)
 {
        struct vmcb_control_area *control = &svm->vmcb->control;
        struct kvm_vcpu *vcpu = &svm->vcpu;
-       struct ghcb *ghcb;
        u64 exit_code;
        u64 reason;
 
-       ghcb = svm->sev_es.ghcb;
-
        /*
         * Retrieve the exit code now even though it may not be marked valid
         * as it could help with debugging.
@@ -2467,7 +2464,7 @@ static int sev_es_validate_vmgexit(struct vcpu_svm *svm)
        exit_code = kvm_ghcb_get_sw_exit_code(control);
 
        /* Only GHCB Usage code 0 is supported */
-       if (ghcb->ghcb_usage) {
+       if (svm->sev_es.ghcb->ghcb_usage) {
                reason = GHCB_ERR_INVALID_USAGE;
                goto vmgexit_err;
        }
@@ -2561,7 +2558,7 @@ static int sev_es_validate_vmgexit(struct vcpu_svm *svm)
 vmgexit_err:
        if (reason == GHCB_ERR_INVALID_USAGE) {
                vcpu_unimpl(vcpu, "vmgexit: ghcb usage %#x is not valid\n",
-                           ghcb->ghcb_usage);
+                           svm->sev_es.ghcb->ghcb_usage);
        } else if (reason == GHCB_ERR_INVALID_EVENT) {
                vcpu_unimpl(vcpu, "vmgexit: exit code %#llx is not valid\n",
                            exit_code);
@@ -2571,8 +2568,8 @@ vmgexit_err:
                dump_ghcb(svm);
        }
 
-       ghcb_set_sw_exit_info_1(ghcb, 2);
-       ghcb_set_sw_exit_info_2(ghcb, reason);
+       ghcb_set_sw_exit_info_1(svm->sev_es.ghcb, 2);
+       ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, reason);
 
        /* Resume the guest to "return" the error code. */
        return 1;
@@ -2637,7 +2634,6 @@ void pre_sev_run(struct vcpu_svm *svm, int cpu)
 static int setup_vmgexit_scratch(struct vcpu_svm *svm, bool sync, u64 len)
 {
        struct vmcb_control_area *control = &svm->vmcb->control;
-       struct ghcb *ghcb = svm->sev_es.ghcb;
        u64 ghcb_scratch_beg, ghcb_scratch_end;
        u64 scratch_gpa_beg, scratch_gpa_end;
        void *scratch_va;
@@ -2713,8 +2709,8 @@ static int setup_vmgexit_scratch(struct vcpu_svm *svm, bool sync, u64 len)
        return 0;
 
 e_scratch:
-       ghcb_set_sw_exit_info_1(ghcb, 2);
-       ghcb_set_sw_exit_info_2(ghcb, GHCB_ERR_INVALID_SCRATCH_AREA);
+       ghcb_set_sw_exit_info_1(svm->sev_es.ghcb, 2);
+       ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, GHCB_ERR_INVALID_SCRATCH_AREA);
 
        return 1;
 }
@@ -2827,7 +2823,6 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
        struct vcpu_svm *svm = to_svm(vcpu);
        struct vmcb_control_area *control = &svm->vmcb->control;
        u64 ghcb_gpa, exit_code;
-       struct ghcb *ghcb;
        int ret;
 
        /* Validate the GHCB */
@@ -2852,17 +2847,16 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
        }
 
        svm->sev_es.ghcb = svm->sev_es.ghcb_map.hva;
-       ghcb = svm->sev_es.ghcb_map.hva;
 
-       trace_kvm_vmgexit_enter(vcpu->vcpu_id, ghcb);
+       trace_kvm_vmgexit_enter(vcpu->vcpu_id, svm->sev_es.ghcb);
 
        sev_es_sync_from_ghcb(svm);
        ret = sev_es_validate_vmgexit(svm);
        if (ret)
                return ret;
 
-       ghcb_set_sw_exit_info_1(ghcb, 0);
-       ghcb_set_sw_exit_info_2(ghcb, 0);
+       ghcb_set_sw_exit_info_1(svm->sev_es.ghcb, 0);
+       ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, 0);
 
        exit_code = kvm_ghcb_get_sw_exit_code(control);
        switch (exit_code) {
@@ -2902,13 +2896,13 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
                        break;
                case 1:
                        /* Get AP jump table address */
-                       ghcb_set_sw_exit_info_2(ghcb, sev->ap_jump_table);
+                       ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, sev->ap_jump_table);
                        break;
                default:
                        pr_err("svm: vmgexit: unsupported AP jump table request - exit_info_1=%#llx\n",
                               control->exit_info_1);
-                       ghcb_set_sw_exit_info_1(ghcb, 2);
-                       ghcb_set_sw_exit_info_2(ghcb, GHCB_ERR_INVALID_INPUT);
+                       ghcb_set_sw_exit_info_1(svm->sev_es.ghcb, 2);
+                       ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, GHCB_ERR_INVALID_INPUT);
                }
 
                ret = 1;