On 10/1/23 19:33, Kalra, Ashish wrote:

On 1/9/2023 8:28 PM, Alexey Kardashevskiy wrote:

quoted

On 10/1/23 10:41, Kalra, Ashish wrote:

quoted

On 1/8/2023 9:33 PM, Alexey Kardashevskiy wrote:

quoted

On 15/12/22 06:40, Michael Roth wrote:

quoted

From: Brijesh Singh <redacted>

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 <redacted>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
Signed-off-by: Michael Roth <redacted>
---
  arch/x86/kvm/svm/sev.c | 185 
+++++++++++++++++++++++++++++++++++++++--
  arch/x86/kvm/svm/svm.h |   2 +
  2 files changed, 181 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 5f2b2092cdae..18efa70553c2 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c

@@ -331,6 +331,7 @@ static int sev_guest_init(struct kvm *kvm, 

struct kvm_sev_cmd *argp)
          if (ret)
              goto e_free;
+        mutex_init(&sev->guest_req_lock);
          ret = sev_snp_init(&argp->error, false);
      } else {
          ret = sev_platform_init(&argp->error);

@@ -2051,23 +2052,34 @@ int sev_vm_move_enc_context_from(struct kvm 

*kvm, unsigned int source_fd)
   */
  static void *snp_context_create(struct kvm *kvm, struct 
kvm_sev_cmd *argp)
  {
+    struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
      struct sev_data_snp_addr data = {};
-    void *context;
+    void *context, *certs_data;
      int rc;
+    /* Allocate memory used for the certs data in SNP guest 
request */
+    certs_data = kzalloc(SEV_FW_BLOB_MAX_SIZE, GFP_KERNEL_ACCOUNT);
+    if (!certs_data)
+        return NULL;
+
      /* Allocate memory for context page */
      context = snp_alloc_firmware_page(GFP_KERNEL_ACCOUNT);
      if (!context)
-        return NULL;
+        goto e_free;
      data.gctx_paddr = __psp_pa(context);
      rc = __sev_issue_cmd(argp->sev_fd, SEV_CMD_SNP_GCTX_CREATE, 
&data, &argp->error);
-    if (rc) {
-        snp_free_firmware_page(context);
-        return NULL;
-    }
+    if (rc)
+        goto e_free;
+
+    sev->snp_certs_data = certs_data;
      return context;
+
+e_free:
+    snp_free_firmware_page(context);
+    kfree(certs_data);
+    return NULL;
  }
  static int snp_bind_asid(struct kvm *kvm, int *error)

@@ -2653,6 +2665,8 @@ static int snp_decommission_context(struct 

kvm *kvm)
      snp_free_firmware_page(sev->snp_context);
      sev->snp_context = NULL;
+    kfree(sev->snp_certs_data);
+
      return 0;
  }

@@ -3174,6 +3188,8 @@ static int sev_es_validate_vmgexit(struct 

vcpu_svm *svm, u64 *exit_code)
      case SVM_VMGEXIT_UNSUPPORTED_EVENT:
      case SVM_VMGEXIT_HV_FEATURES:
      case SVM_VMGEXIT_PSC:
+    case SVM_VMGEXIT_GUEST_REQUEST:
+    case SVM_VMGEXIT_EXT_GUEST_REQUEST:
          break;
      default:
          reason = GHCB_ERR_INVALID_EVENT;

@@ -3396,6 +3412,149 @@ static int snp_complete_psc(struct kvm_vcpu 

*vcpu)
      return 1;
  }
+static unsigned long snp_setup_guest_buf(struct vcpu_svm *svm,
+                     struct sev_data_snp_guest_request *data,
+                     gpa_t req_gpa, gpa_t resp_gpa)
+{
+    struct kvm_vcpu *vcpu = &svm->vcpu;
+    struct kvm *kvm = vcpu->kvm;
+    kvm_pfn_t req_pfn, resp_pfn;
+    struct kvm_sev_info *sev;
+
+    sev = &to_kvm_svm(kvm)->sev_info;
+
+    if (!IS_ALIGNED(req_gpa, PAGE_SIZE) || !IS_ALIGNED(resp_gpa, 
PAGE_SIZE))
+        return SEV_RET_INVALID_PARAM;
+
+    req_pfn = gfn_to_pfn(kvm, gpa_to_gfn(req_gpa));
+    if (is_error_noslot_pfn(req_pfn))
+        return SEV_RET_INVALID_ADDRESS;
+
+    resp_pfn = gfn_to_pfn(kvm, gpa_to_gfn(resp_gpa));
+    if (is_error_noslot_pfn(resp_pfn))
+        return SEV_RET_INVALID_ADDRESS;
+
+    if (rmp_make_private(resp_pfn, 0, PG_LEVEL_4K, 0, true))
+        return SEV_RET_INVALID_ADDRESS;
+
+    data->gctx_paddr = __psp_pa(sev->snp_context);
+    data->req_paddr = __sme_set(req_pfn << PAGE_SHIFT);
+    data->res_paddr = __sme_set(resp_pfn << PAGE_SHIFT);
+
+    return 0;
+}
+
+static void snp_cleanup_guest_buf(struct 
sev_data_snp_guest_request *data, unsigned long *rc)
+{
+    u64 pfn = __sme_clr(data->res_paddr) >> PAGE_SHIFT;
+    int ret;
+
+    ret = snp_page_reclaim(pfn);
+    if (ret)
+        *rc = SEV_RET_INVALID_ADDRESS;
+
+    ret = rmp_make_shared(pfn, PG_LEVEL_4K);
+    if (ret)
+        *rc = SEV_RET_INVALID_ADDRESS;
+}
+
+static void snp_handle_guest_request(struct vcpu_svm *svm, gpa_t 
req_gpa, gpa_t resp_gpa)
+{
+    struct sev_data_snp_guest_request data = {0};
+    struct kvm_vcpu *vcpu = &svm->vcpu;
+    struct kvm *kvm = vcpu->kvm;
+    struct kvm_sev_info *sev;
+    unsigned long rc;
+    int err;
+
+    if (!sev_snp_guest(vcpu->kvm)) {
+        rc = SEV_RET_INVALID_GUEST;
+        goto e_fail;
+    }
+
+    sev = &to_kvm_svm(kvm)->sev_info;
+
+    mutex_lock(&sev->guest_req_lock);
+
+    rc = snp_setup_guest_buf(svm, &data, req_gpa, resp_gpa);
+    if (rc)
+        goto unlock;
+
+    rc = sev_issue_cmd(kvm, SEV_CMD_SNP_GUEST_REQUEST, &data, &err);

This one goes via sev_issue_cmd_external_user() and uses sev-fd...

quoted

+    if (rc)
+        /* use the firmware error code */
+        rc = err;
+
+    snp_cleanup_guest_buf(&data, &rc);
+
+unlock:
+    mutex_unlock(&sev->guest_req_lock);
+
+e_fail:
+    svm_set_ghcb_sw_exit_info_2(vcpu, rc);
+}
+
+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;
+    }
+
+    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);

but this one does not and jump straight to 
drivers/crypto/ccp/sev-dev.c ignoring sev->fd. Why different? Can 
these two be unified? sev_issue_cmd_external_user() only checks if 
fd is /dev/sev which is hardly useful.

"[PATCH RFC v7 32/64] crypto: ccp: Provide APIs to query extended 
attestation report" added this one.

SNP_EXT_GUEST_REQUEST additionally returns a certificate blob and 
that's why it goes through the CCP driver interface 
snp_guest_ext_guest_request() that is used to get both the report and 
certificate data/blob at the same time.

True. I thought though that this calls for extending sev_issue_cmd() 
to take care of these extra parameters rather than just skipping the 
sev->fd.

quoted

All the FW API calls on the KVM side go through sev_issue_cmd() and 
sev_issue_cmd_external_user() interfaces and that i believe uses 
sev->fd more of as a sanity check.

Does not look like it:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/crypto/ccp/sev-dev.c?h=v6.2-rc3#n1290

===
int sev_issue_cmd_external_user(struct file *filep, unsigned int cmd,
                 void *data, int *error)
{
     if (!filep || filep->f_op != &sev_fops)
         return -EBADF;

     return sev_do_cmd(cmd, data, error);
}
EXPORT_SYMBOL_GPL(sev_issue_cmd_external_user);
===

The only "more" is that it requires sev->fd to be a valid open fd, 
what is the value in that? I may easily miss the bigger picture here. 
Thanks,

Have a look at following functions in drivers/crypto/ccp/sev-dev.c:
sev_dev_init() and sev_misc_init().

static int sev_misc_init(struct sev_device *sev)
{
         struct device *dev = sev->dev;
         int ret;

         /*
          * SEV feature support can be detected on multiple devices but
          * the SEV FW commands must be issued on the master. During
          * probe, we do not know the master hence we create /dev/sev on
          * the first device probe.
          * sev_do_cmd() finds the right master device to which to issue
          * the command to the firmware.
      */

It is still a single /dev/sev node and the userspace cannot get it 
wrong, it does not have to choose between (for instance) /dev/sev0 and 
/dev/sev1 on a 2 SOC system.

...
...

Hence, sev_issue_cmd_external_user() needs to ensure that the correct 
device (master device) is being operated upon and that's why there is 
the check for file operations matching sev_fops as below :

int sev_issue_cmd_external_user(struct file *filep, unsigned int cmd,
                                 void *data, int *error)
{
         if (!filep || filep->f_op != &sev_fops)
                 return -EBADF;
..
..

Essentially, sev->fd is the misc. device created for the master PSP 
device on which the SEV/SNP firmware commands are issued, hence,
sev_issue_cmd() uses sev->fd.

There is always just one fd which always uses psp_master, nothing from 
that fd is used.

More to the point, if sev->fd is still important, why is it ok to skip 
it for snp_handle_ext_guest_request()? Thanks,


-- 
Alexey