diff mbox series

[v1,24/26] crypto: ccp: Add the SNP_PLATFORM_STATUS command

Message ID 20231230161954.569267-25-michael.roth@amd.com (mailing list archive)
State Not Applicable
Delegated to: Herbert Xu
Headers show
Series Add AMD Secure Nested Paging (SEV-SNP) Initialization Support | expand

Commit Message

Michael Roth Dec. 30, 2023, 4:19 p.m. UTC 
From: Brijesh Singh <brijesh.singh@amd.com>

This command is used to query the SNP platform status. See the SEV-SNP
spec for more details.

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 Documentation/virt/coco/sev-guest.rst | 27 ++++++++++++++++
 drivers/crypto/ccp/sev-dev.c          | 45 +++++++++++++++++++++++++++
 include/uapi/linux/psp-sev.h          |  1 +
 3 files changed, 73 insertions(+)

Comments

Borislav Petkov Jan. 21, 2024, 12:29 p.m. UTC | #1 
On Sat, Dec 30, 2023 at 10:19:52AM -0600, Michael Roth wrote:
> +	/* Change the page state before accessing it */
> +	if (snp_reclaim_pages(__pa(data), 1, true)) {
> +		snp_leak_pages(__pa(data) >> PAGE_SHIFT, 1);
> +		return -EFAULT;
> +	}

This looks weird and it doesn't explain why this needs to happen.
SNP_PLATFORM_STATUS text doesn't explain either.

So, what's up?
Michael Roth Jan. 26, 2024, 3:32 a.m. UTC | #2 
On Sun, Jan 21, 2024 at 01:29:20PM +0100, Borislav Petkov wrote:
> On Sat, Dec 30, 2023 at 10:19:52AM -0600, Michael Roth wrote:
> > +	/* Change the page state before accessing it */
> > +	if (snp_reclaim_pages(__pa(data), 1, true)) {
> > +		snp_leak_pages(__pa(data) >> PAGE_SHIFT, 1);
> > +		return -EFAULT;
> > +	}
> 
> This looks weird and it doesn't explain why this needs to happen.
> SNP_PLATFORM_STATUS text doesn't explain either.
> 
> So, what's up?

I've adding some clarifying comment in v2, but the page that firmware
writes needs to first be switched to the Firmware-owned state, and
after successful completion it will be put in Reclaim state. But it's
possible a failure might occur before that transition is made by
firmware, maybe the command fails somewhere in the callstack before it
even reaches firmware.

If that happens the page might still be in firmware-owned state, and
need to go through snp_reclaim_pages()/SNP_PAGE_RECLAIM before it can
be switched back to Default state.

Rather than trying to special-case all these possibilities, it's simpler
to just always use snp_reclaim_pages(), which will handle both Reclaim
and Firmware-owned pages.

However, snp_reclaim_pages() will already leak the page when necessary,
so I've dropped that bit.

-Mike

> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette
diff mbox series

Patch

diff --git a/Documentation/virt/coco/sev-guest.rst b/Documentation/virt/coco/sev-guest.rst
index 68b0d2363af8..6d3d5d336e5f 100644
--- a/Documentation/virt/coco/sev-guest.rst
+++ b/Documentation/virt/coco/sev-guest.rst
@@ -67,6 +67,22 @@  counter (e.g. counter overflow), then -EIO will be returned.
                 };
         };
 
+The host ioctls are issued to a file descriptor of the /dev/sev device.
+The ioctl accepts the command ID/input structure documented below.
+
+::
+        struct sev_issue_cmd {
+                /* Command ID */
+                __u32 cmd;
+
+                /* Command request structure */
+                __u64 data;
+
+                /* Firmware error code on failure (see psp-sev.h) */
+                __u32 error;
+        };
+
+
 2.1 SNP_GET_REPORT
 ------------------
 
@@ -124,6 +140,17 @@  be updated with the expected value.
 
 See GHCB specification for further detail on how to parse the certificate blob.
 
+2.4 SNP_PLATFORM_STATUS
+-----------------------
+:Technology: sev-snp
+:Type: hypervisor ioctl cmd
+:Parameters (out): struct sev_user_data_snp_status
+:Returns (out): 0 on success, -negative on error
+
+The SNP_PLATFORM_STATUS command is used to query the SNP platform status. The
+status includes API major, minor version and more. See the SEV-SNP
+specification for further details.
+
 3. SEV-SNP CPUID Enforcement
 ============================
 
diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index 598878e760bc..e663175cfa44 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -1962,6 +1962,48 @@  static int sev_ioctl_do_pdh_export(struct sev_issue_cmd *argp, bool writable)
 	return ret;
 }
 
+static int sev_ioctl_do_snp_platform_status(struct sev_issue_cmd *argp)
+{
+	struct sev_device *sev = psp_master->sev_data;
+	struct sev_data_snp_addr buf;
+	struct page *status_page;
+	void *data;
+	int ret;
+
+	if (!sev->snp_initialized || !argp->data)
+		return -EINVAL;
+
+	status_page = alloc_page(GFP_KERNEL_ACCOUNT);
+	if (!status_page)
+		return -ENOMEM;
+
+	data = page_address(status_page);
+	if (rmp_mark_pages_firmware(__pa(data), 1, true)) {
+		ret = -EFAULT;
+		goto cleanup;
+	}
+
+	buf.gctx_paddr = __psp_pa(data);
+	ret = __sev_do_cmd_locked(SEV_CMD_SNP_PLATFORM_STATUS, &buf, &argp->error);
+
+	/* Change the page state before accessing it */
+	if (snp_reclaim_pages(__pa(data), 1, true)) {
+		snp_leak_pages(__pa(data) >> PAGE_SHIFT, 1);
+		return -EFAULT;
+	}
+
+	if (ret)
+		goto cleanup;
+
+	if (copy_to_user((void __user *)argp->data, data,
+			 sizeof(struct sev_user_data_snp_status)))
+		ret = -EFAULT;
+
+cleanup:
+	__free_pages(status_page, 0);
+	return ret;
+}
+
 static long sev_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
 {
 	void __user *argp = (void __user *)arg;
@@ -2013,6 +2055,9 @@  static long sev_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
 	case SEV_GET_ID2:
 		ret = sev_ioctl_do_get_id2(&input);
 		break;
+	case SNP_PLATFORM_STATUS:
+		ret = sev_ioctl_do_snp_platform_status(&input);
+		break;
 	default:
 		ret = -EINVAL;
 		goto out;
diff --git a/include/uapi/linux/psp-sev.h b/include/uapi/linux/psp-sev.h
index 71ba5f9f90a8..1feba7d08099 100644
--- a/include/uapi/linux/psp-sev.h
+++ b/include/uapi/linux/psp-sev.h
@@ -28,6 +28,7 @@  enum {
 	SEV_PEK_CERT_IMPORT,
 	SEV_GET_ID,	/* This command is deprecated, use SEV_GET_ID2 */
 	SEV_GET_ID2,
+	SNP_PLATFORM_STATUS,
 
 	SEV_MAX,
 };