[PATCH 3/3] x86/sev: add a SVSM vTPM platform device

Stefano Garzarella
2024-12-10T14:35:03Z

From: James Bottomley <James.Bottomley@HansenPartnership.com>

If the SNP boot has a SVSM, probe for the vTPM device by sending a
SVSM_VTPM_QUERY call (function 8). The SVSM will return a bitmap with
the TPM_SEND_COMMAND bit set only if the vTPM is present and it is able
to handle TPM commands at runtime.

If a vTPM is found, register a platform device as "platform:tpm" so it
can be attached to the tpm_platform.c driver.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
[CC] Used SVSM_VTPM_QUERY to probe the TPM
Signed-off-by: Claudio Carvalho <cclaudio@linux.ibm.com>
[SG] Code adjusted with some changes introduced in 6.11
[SG] Used macro for SVSM_VTPM_CALL
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
arch/x86/coco/sev/core.c | 64 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 64 insertions(+)

diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index c5b0148b8c0a..ec0153fddc9e 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -21,6 +21,7 @@
#include <linux/cpumask.h>
#include <linux/efi.h>
#include <linux/platform_device.h>
+#include <linux/tpm_platform.h>
#include <linux/io.h>
#include <linux/psp-sev.h>
#include <linux/dmi.h>
@@ -2578,6 +2579,51 @@ static struct platform_device sev_guest_device = {
.id = -1,
};

+static struct platform_device tpm_device = {
+ .name = "tpm",
+ .id = -1,
+};
+
+static int snp_issue_svsm_vtpm_send_command(u8 *buffer)
+{
+ struct svsm_call call = {};
+
+ call.caa = svsm_get_caa();
+ call.rax = SVSM_VTPM_CALL(SVSM_VTPM_CMD);
+ call.rcx = __pa(buffer);
+
+ return svsm_perform_call_protocol(&call);
+}
+
+static bool is_svsm_vtpm_send_command_supported(void)
+{
+ struct svsm_call call = {};
+ u64 send_cmd_mask = 0;
+ u64 platform_cmds;
+ u64 features;
+ int ret;
+
+ call.caa = svsm_get_caa();
+ call.rax = SVSM_VTPM_CALL(SVSM_VTPM_QUERY);
+
+ ret = svsm_perform_call_protocol(&call);
+
+ if (ret != SVSM_SUCCESS)
+ return false;
+
+ features = call.rdx_out;
+ platform_cmds = call.rcx_out;
+
+ /* No feature supported, it must be zero */
+ if (features)
+ return false;
+
+ /* TPM_SEND_COMMAND - platform command 8 */
+ send_cmd_mask = 1 << 8;
+
+ return (platform_cmds & send_cmd_mask) == send_cmd_mask;
+}
+
static int __init snp_init_platform_device(void)
{
struct sev_guest_platform_data data;
@@ -2593,6 +2639,24 @@ static int __init snp_init_platform_device(void)
return -ENODEV;

pr_info("SNP guest platform device initialized.\n");
+
+ /*
+ * The VTPM device is available only if we have a SVSM and
+ * its VTPM supports the TPM_SEND_COMMAND platform command
+ */
+ if (IS_ENABLED(CONFIG_TCG_PLATFORM) && snp_vmpl &&
+ is_svsm_vtpm_send_command_supported()) {
+ struct tpm_platform_ops pops = {
+ .sendrcv = snp_issue_svsm_vtpm_send_command,
+ };
+
+ if (platform_device_add_data(&tpm_device, &pops, sizeof(pops)))
+ return -ENODEV;
+ if (platform_device_register(&tpm_device))
+ return -ENODEV;
+ pr_info("SNP SVSM VTPM platform device initialized\n");
+ }
+
return 0;
}
device_initcall(snp_init_platform_device);
--
2.47.1