KVM: SEV: Return appropriate error codes if SEV-ES scratch setup fails

Return appropriate error codes if setting up the GHCB scratch area for an
SEV-ES guest fails.  In particular, returning -EINVAL instead of -ENOMEM
when allocating the kernel buffer could be confusing as userspace would
likely suspect a guest issue.

Fixes: 8f423a80d299 ("KVM: SVM: Support MMIO for an SEV-ES guest")
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211109222350.2266045-2-seanjc@google.com>
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 59727a966f902be47413eb7a88e71626a13d027d..f35f59bfdb415b47e048c94c21e4d61c0f2bae9e 100644 (file)
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2530,7 +2530,7 @@ void pre_sev_run(struct vcpu_svm *svm, int cpu)
 }
 
 #define GHCB_SCRATCH_AREA_LIMIT                (16ULL * PAGE_SIZE)
-static bool setup_vmgexit_scratch(struct vcpu_svm *svm, bool sync, u64 len)
+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;
@@ -2541,14 +2541,14 @@ static bool setup_vmgexit_scratch(struct vcpu_svm *svm, bool sync, u64 len)
        scratch_gpa_beg = ghcb_get_sw_scratch(ghcb);
        if (!scratch_gpa_beg) {
                pr_err("vmgexit: scratch gpa not provided\n");
-               return false;
+               return -EINVAL;
        }
 
        scratch_gpa_end = scratch_gpa_beg + len;
        if (scratch_gpa_end < scratch_gpa_beg) {
                pr_err("vmgexit: scratch length (%#llx) not valid for scratch address (%#llx)\n",
                       len, scratch_gpa_beg);
-               return false;
+               return -EINVAL;
        }
 
        if ((scratch_gpa_beg & PAGE_MASK) == control->ghcb_gpa) {
@@ -2566,7 +2566,7 @@ static bool setup_vmgexit_scratch(struct vcpu_svm *svm, bool sync, u64 len)
                    scratch_gpa_end > ghcb_scratch_end) {
                        pr_err("vmgexit: scratch area is outside of GHCB shared buffer area (%#llx - %#llx)\n",
                               scratch_gpa_beg, scratch_gpa_end);
-                       return false;
+                       return -EINVAL;
                }
 
                scratch_va = (void *)svm->sev_es.ghcb;
@@ -2579,18 +2579,18 @@ static bool setup_vmgexit_scratch(struct vcpu_svm *svm, bool sync, u64 len)
                if (len > GHCB_SCRATCH_AREA_LIMIT) {
                        pr_err("vmgexit: scratch area exceeds KVM limits (%#llx requested, %#llx limit)\n",
                               len, GHCB_SCRATCH_AREA_LIMIT);
-                       return false;
+                       return -EINVAL;
                }
                scratch_va = kzalloc(len, GFP_KERNEL_ACCOUNT);
                if (!scratch_va)
-                       return false;
+                       return -ENOMEM;
 
                if (kvm_read_guest(svm->vcpu.kvm, scratch_gpa_beg, scratch_va, len)) {
                        /* Unable to copy scratch area from guest */
                        pr_err("vmgexit: kvm_read_guest for scratch area failed\n");
 
                        kfree(scratch_va);
-                       return false;
+                       return -EFAULT;
                }
 
                /*
@@ -2606,7 +2606,7 @@ static bool setup_vmgexit_scratch(struct vcpu_svm *svm, bool sync, u64 len)
        svm->sev_es.ghcb_sa = scratch_va;
        svm->sev_es.ghcb_sa_len = len;
 
-       return true;
+       return 0;
 }
 
 static void set_ghcb_msr_bits(struct vcpu_svm *svm, u64 value, u64 mask,
@@ -2745,10 +2745,10 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
        ghcb_set_sw_exit_info_1(ghcb, 0);
        ghcb_set_sw_exit_info_2(ghcb, 0);
 
-       ret = -EINVAL;
        switch (exit_code) {
        case SVM_VMGEXIT_MMIO_READ:
-               if (!setup_vmgexit_scratch(svm, true, control->exit_info_2))
+               ret = setup_vmgexit_scratch(svm, true, control->exit_info_2);
+               if (ret)
                        break;
 
                ret = kvm_sev_es_mmio_read(vcpu,
@@ -2757,7 +2757,8 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
                                           svm->sev_es.ghcb_sa);
                break;
        case SVM_VMGEXIT_MMIO_WRITE:
-               if (!setup_vmgexit_scratch(svm, false, control->exit_info_2))
+               ret = setup_vmgexit_scratch(svm, false, control->exit_info_2);
+               if (ret)
                        break;
 
                ret = kvm_sev_es_mmio_write(vcpu,
@@ -2800,6 +2801,7 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
                vcpu_unimpl(vcpu,
                            "vmgexit: unsupported event - exit_info_1=%#llx, exit_info_2=%#llx\n",
                            control->exit_info_1, control->exit_info_2);
+               ret = -EINVAL;
                break;
        default:
                ret = svm_invoke_exit_handler(vcpu, exit_code);
@@ -2812,6 +2814,7 @@ int sev_es_string_io(struct vcpu_svm *svm, int size, unsigned int port, int in)
 {
        int count;
        int bytes;
+       int r;
 
        if (svm->vmcb->control.exit_info_2 > INT_MAX)
                return -EINVAL;
@@ -2820,8 +2823,9 @@ int sev_es_string_io(struct vcpu_svm *svm, int size, unsigned int port, int in)
        if (unlikely(check_mul_overflow(count, size, &bytes)))
                return -EINVAL;
 
-       if (!setup_vmgexit_scratch(svm, in, bytes))
-               return -EINVAL;
+       r = setup_vmgexit_scratch(svm, in, bytes);
+       if (r)
+               return r;
 
        return kvm_sev_es_string_io(&svm->vcpu, size, port, svm->sev_es.ghcb_sa,
                                    count, in);