Re: [PATCH Part2 v6 42/49] KVM: SVM: Provide support for SNP_GUEST_REQUEST NAE event
From: Tom Lendacky
Date: Fri Oct 21 2022 - 17:31:03 EST
On 10/21/22 16:12, Kalra, Ashish wrote:
Hello Tom,
On 10/21/2022 2:06 PM, Tom Lendacky wrote:
On 6/20/22 18:13, Ashish Kalra wrote:
From: Brijesh Singh <brijesh.singh@xxxxxxx>
Version 2 of GHCB specification added the support for two SNP Guest
Request Message NAE events. The events allows for an SEV-SNP guest to
make request to the SEV-SNP firmware through hypervisor using the
SNP_GUEST_REQUEST API define in the SEV-SNP firmware specification.
The SNP_EXT_GUEST_REQUEST is similar to SNP_GUEST_REQUEST with the
difference of an additional certificate blob that can be passed through
the SNP_SET_CONFIG ioctl defined in the CCP driver. The CCP driver
provides snp_guest_ext_guest_request() that is used by the KVM to get
both the report and certificate data at once.
Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
---
arch/x86/kvm/svm/sev.c | 196 +++++++++++++++++++++++++++++++++++++++--
arch/x86/kvm/svm/svm.h | 2 +
2 files changed, 192 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 7fc0fad87054..089af21a4efe 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
+static void snp_handle_ext_guest_request(struct vcpu_svm *svm, gpa_t
req_gpa, gpa_t resp_gpa)
+{
+ struct sev_data_snp_guest_request req = {0};
+ struct kvm_vcpu *vcpu = &svm->vcpu;
+ struct kvm *kvm = vcpu->kvm;
+ unsigned long data_npages;
+ struct kvm_sev_info *sev;
+ unsigned long rc, err;
+ u64 data_gpa;
+
+ if (!sev_snp_guest(vcpu->kvm)) {
+ rc = SEV_RET_INVALID_GUEST;
+ goto e_fail;
+ }
+
+ sev = &to_kvm_svm(kvm)->sev_info;
+
+ data_gpa = vcpu->arch.regs[VCPU_REGS_RAX];
+ data_npages = vcpu->arch.regs[VCPU_REGS_RBX];
+
+ if (!IS_ALIGNED(data_gpa, PAGE_SIZE)) {
+ rc = SEV_RET_INVALID_ADDRESS;
+ goto e_fail;
+ }
+
+ /* Verify that requested blob will fit in certificate buffer */
+ if ((data_npages << PAGE_SHIFT) > SEV_FW_BLOB_MAX_SIZE) {
Not sure this is a valid check... Isn't it OK if the guest has supplied
more room than is required? If the guest supplies 8 pages and the
hypervisor only needs to copy 1 page of data (or the
SEV_FW_BLOB_MAX_SIZE number of pages) that shouldn't be an error. I
think this check can go, right?
Agreed.
The check should probably be
if ((data_npages << PAGE_SHIFT) < SEV_FW_BLOB_MAX_SIZE)
No, the check should just be removed. If the number of pages required to
hold the cert data is only 1, then a data_npages value of 1 is just fine
(see below).
and that check already exists in:
snp_guest_ext_guest_request(...)
{
...
...
/*
* Check if there is enough space to copy the certificate chain.
Otherwise
* return ERROR code defined in the GHCB specification.
*/
expected_npages = sev->snp_certs_len >> PAGE_SHIFT;
if (*npages < expected_npages) {
If expected_npages is 1, then an *npages value of 1 is OK. But if you put
the check in above that you want, you would never get here with an *npages
value of 1.
Thanks,
Tom
*npages = expected_npages;
*fw_err = SNP_GUEST_REQ_INVALID_LEN;
return -EINVAL;
}
...
Thanks,
Ashish
Thanks,
Tom
+ rc = SEV_RET_INVALID_PARAM;
+ goto e_fail;
+ }
+
+ mutex_lock(&sev->guest_req_lock);
+
+ rc = snp_setup_guest_buf(svm, &req, req_gpa, resp_gpa);
+ if (rc)
+ goto unlock;
+
+ rc = snp_guest_ext_guest_request(&req, (unsigned
long)sev->snp_certs_data,
+ &data_npages, &err);
+ if (rc) {
+ /*
+ * If buffer length is small then return the expected
+ * length in rbx.
+ */
+ if (err == SNP_GUEST_REQ_INVALID_LEN)
+ vcpu->arch.regs[VCPU_REGS_RBX] = data_npages;
+
+ /* pass the firmware error code */
+ rc = err;
+ goto cleanup;
+ }
+
+ /* Copy the certificate blob in the guest memory */
+ if (data_npages &&
+ kvm_write_guest(kvm, data_gpa, sev->snp_certs_data,
data_npages << PAGE_SHIFT))
+ rc = SEV_RET_INVALID_ADDRESS;
+
+cleanup:
+ snp_cleanup_guest_buf(&req, &rc);
+
+unlock:
+ mutex_unlock(&sev->guest_req_lock);
+
+e_fail:
+ svm_set_ghcb_sw_exit_info_2(vcpu, rc);
+}
+