[PATCH v1 20/26] crypto: ccp: Add debug support for decrypting pages

[Michael Roth <michael.roth@amd.com>]

From: Brijesh Singh <brijesh.singh@amd.com>

Add support to decrypt guest encrypted memory. These API interfaces can
be used for example to dump VMCBs on SNP guest exit.

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
[mdr: minor commit fixups]
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 drivers/crypto/ccp/sev-dev.c | 32 ++++++++++++++++++++++++++++++++
 include/linux/psp-sev.h      | 19 +++++++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index 47fc58ed9e6a..9792c7af3005 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -2053,6 +2053,38 @@ int sev_guest_df_flush(int *error)
 }
 EXPORT_SYMBOL_GPL(sev_guest_df_flush);
 
+int snp_guest_dbg_decrypt_page(u64 gctx_pfn, u64 src_pfn, u64 dst_pfn, int *error)
+{
+	struct sev_data_snp_dbg data = {0};
+	struct sev_device *sev;
+	int ret;
+
+	if (!psp_master || !psp_master->sev_data)
+		return -ENODEV;
+
+	sev = psp_master->sev_data;
+
+	if (!sev->snp_initialized)
+		return -EINVAL;
+
+	data.gctx_paddr = sme_me_mask | (gctx_pfn << PAGE_SHIFT);
+	data.src_addr = sme_me_mask | (src_pfn << PAGE_SHIFT);
+	data.dst_addr = sme_me_mask | (dst_pfn << PAGE_SHIFT);
+
+	/* The destination page must be in the firmware state. */
+	if (rmp_mark_pages_firmware(data.dst_addr, 1, false))
+		return -EIO;
+
+	ret = sev_do_cmd(SEV_CMD_SNP_DBG_DECRYPT, &data, error);
+
+	/* Restore the page state */
+	if (snp_reclaim_pages(data.dst_addr, 1, false))
+		ret = -EIO;
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(snp_guest_dbg_decrypt_page);
+
 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 16d0da895680..b14008388a37 100644
--- a/include/linux/psp-sev.h
+++ b/include/linux/psp-sev.h
@@ -930,6 +930,20 @@ int sev_guest_decommission(struct sev_data_decommission *data, int *error);
  */
 int sev_do_cmd(int cmd, void *data, int *psp_ret);
 
+/**
+ * snp_guest_dbg_decrypt_page - perform SEV SNP_DBG_DECRYPT command
+ *
+ * @sev_ret: sev command return code
+ *
+ * Returns:
+ * 0 if the SEV successfully processed the command
+ * -%ENODEV    if the SEV device is not available
+ * -%ENOTSUPP  if the SEV does not support SEV
+ * -%ETIMEDOUT if the SEV command timed out
+ * -%EIO       if the SEV returned a non-zero return code
+ */
+int snp_guest_dbg_decrypt_page(u64 gctx_pfn, u64 src_pfn, u64 dst_pfn, int *error);
+
 void *psp_copy_user_blob(u64 uaddr, u32 len);
 void *snp_alloc_firmware_page(gfp_t mask);
 void snp_free_firmware_page(void *addr);
@@ -960,6 +974,11 @@ sev_issue_cmd_external_user(struct file *filep, unsigned int id, void *data, int
 
 static inline void *psp_copy_user_blob(u64 __user uaddr, u32 len) { return ERR_PTR(-EINVAL); }
 
+static inline int snp_guest_dbg_decrypt_page(u64 gctx_pfn, u64 src_pfn, u64 dst_pfn, int *error)
+{
+	return -ENODEV;
+}
+
 static inline void *snp_alloc_firmware_page(gfp_t mask)
 {
 	return NULL;
-- 
2.25.1