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Subject[PATCH 1/2] KVM: SEV: Return appropriate error codes if SEV-ES scratch setup fails
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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>
---
arch/x86/kvm/svm/sev.c | 31 ++++++++++++++++++-------------
1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 3e2769855e51..ea8069c9b5cb 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2299,7 +2299,7 @@ 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->ghcb;
@@ -2310,14 +2310,14 @@ 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) {
@@ -2335,7 +2335,7 @@ 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->ghcb;
@@ -2348,18 +2348,18 @@ 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;
}

/*
@@ -2375,7 +2375,7 @@ static bool setup_vmgexit_scratch(struct vcpu_svm *svm, bool sync, u64 len)
svm->ghcb_sa = scratch_va;
svm->ghcb_sa_len = len;

- return true;
+ return 0;
}

static void set_ghcb_msr_bits(struct vcpu_svm *svm, u64 value, u64 mask,
@@ -2514,10 +2514,10 @@ 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,
@@ -2526,7 +2526,8 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
svm->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,
@@ -2569,6 +2570,7 @@ 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);
@@ -2579,8 +2581,11 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)

int sev_es_string_io(struct vcpu_svm *svm, int size, unsigned int port, int in)
{
- if (!setup_vmgexit_scratch(svm, in, svm->vmcb->control.exit_info_2))
- return -EINVAL;
+ int r;
+
+ r = setup_vmgexit_scratch(svm, in, svm->vmcb->control.exit_info_2);
+ if (r)
+ return r;

return kvm_sev_es_string_io(&svm->vcpu, size, port,
svm->ghcb_sa, svm->ghcb_sa_len / size, in);
--
2.34.0.rc0.344.g81b53c2807-goog
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