On 10/09/2021 6:30, Marc Orr wrote:

On Fri, Aug 20, 2021 at 9:00 AM Brijesh Singh [off-list ref] wrote:

quoted

Version 2 of the GHCB specification defines VMGEXIT that is used to get
the extended attestation report. The extended attestation report includes
the certificate blobs provided through the SNP_SET_EXT_CONFIG.

The snp_guest_ext_guest_request() will be used by the hypervisor to get
the extended attestation report. See the GHCB specification for more
details.

Signed-off-by: Brijesh Singh <redacted>
---
 drivers/crypto/ccp/sev-dev.c | 43 ++++++++++++++++++++++++++++++++++++
 include/linux/psp-sev.h      | 24 ++++++++++++++++++++
 2 files changed, 67 insertions(+)

diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index 9ba194acbe85..e2650c3d0d0a 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c

@@ -22,6 +22,7 @@
 #include <linux/firmware.h>
 #include <linux/gfp.h>
 #include <linux/cpufeature.h>
+#include <linux/sev-guest.h>

 #include <asm/smp.h>

@@ -1677,6 +1678,48 @@ int snp_guest_dbg_decrypt(struct sev_data_snp_dbg *data, int *error)
 }
 EXPORT_SYMBOL_GPL(snp_guest_dbg_decrypt);

+int snp_guest_ext_guest_request(struct sev_data_snp_guest_request *data,
+                               unsigned long vaddr, unsigned long *npages, unsigned long *fw_err)
+{
+       unsigned long expected_npages;
+       struct sev_device *sev;
+       int rc;
+
+       if (!psp_master || !psp_master->sev_data)
+               return -ENODEV;
+
+       sev = psp_master->sev_data;
+
+       if (!sev->snp_inited)
+               return -EINVAL;
+
+       /*
+        * 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;

Is this calculation for `expected_npages` correct? Assume that
`sev->snp_certs_len` is less than a page (e.g., 2000). Then, this
calculation will return `0` for `expected_npages`, rather than round
up to 1.

In patch 17 in sev_ioctl_snp_set_config there's a check that certs_len
is aligned to PAGE_SIZE (and this value is later in that function assigned
to sev->snp_certs_len):

+	/* Copy the certs from userspace */
+	if (input.certs_address) {
+		if (!input.certs_len || !IS_ALIGNED(input.certs_len, PAGE_SIZE))
+			return -EINVAL;

but I agree that rounding up (DIV_ROUND_UP) or asserting that
sev->snp_certs_len is aligned to PAGE_SIZE (and non-zero) makes
sense here.


-Dov

quoted

+       if (*npages < expected_npages) {
+               *npages = expected_npages;
+               *fw_err = SNP_GUEST_REQ_INVALID_LEN;
+               return -EINVAL;
+       }
+
+       rc = sev_do_cmd(SEV_CMD_SNP_GUEST_REQUEST, data, (int *)&fw_err);
+       if (rc)
+               return rc;
+
+       /* Copy the certificate blob */
+       if (sev->snp_certs_data) {
+               *npages = expected_npages;
+               memcpy((void *)vaddr, sev->snp_certs_data, *npages << PAGE_SHIFT);
+       } else {
+               *npages = 0;
+       }
+
+       return rc;
+}
+EXPORT_SYMBOL_GPL(snp_guest_ext_guest_request);
+
 static void sev_exit(struct kref *ref)
 {
        misc_deregister(&misc_dev->misc);

diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
index 00bd684dc094..ea94ce4d834a 100644
--- a/include/linux/psp-sev.h
+++ b/include/linux/psp-sev.h

@@ -924,6 +924,23 @@ void *psp_copy_user_blob(u64 uaddr, u32 len);
 void *snp_alloc_firmware_page(gfp_t mask);
 void snp_free_firmware_page(void *addr);

+/**
+ * snp_guest_ext_guest_request - perform the SNP extended guest request command
+ *  defined in the GHCB specification.
+ *
+ * @data: the input guest request structure
+ * @vaddr: address where the certificate blob need to be copied.
+ * @npages: number of pages for the certificate blob.
+ *    If the specified page count is less than the certificate blob size, then the
+ *    required page count is returned with error code defined in the GHCB spec.
+ *    If the specified page count is more than the certificate blob size, then
+ *    page count is updated to reflect the amount of valid data copied in the
+ *    vaddr.
+ */
+int snp_guest_ext_guest_request(struct sev_data_snp_guest_request *data,
+                               unsigned long vaddr, unsigned long *npages,
+                               unsigned long *error);
+
 #else  /* !CONFIG_CRYPTO_DEV_SP_PSP */

 static inline int

@@ -971,6 +988,13 @@ static inline void *snp_alloc_firmware_page(gfp_t mask)

 static inline void snp_free_firmware_page(void *addr) { }

+static inline int snp_guest_ext_guest_request(struct sev_data_snp_guest_request *data,
+                                             unsigned long vaddr, unsigned long *n,
+                                             unsigned long *error)
+{
+       return -ENODEV;
+}
+
 #endif /* CONFIG_CRYPTO_DEV_SP_PSP */

 #endif /* __PSP_SEV_H__ */
--

2.17.1