[RFC PATCH v2 2/6] x86/sev: add SVSM vTPM probe/send_command functions

Stefano Garzarella
2025-02-28T17:07:45Z

Add two new functions to probe and send commands to the SVSM vTPM.
They leverage the two calls defined by the AMD SVSM specification
for the vTPM protocol: SVSM_VTPM_QUERY and SVSM_VTPM_CMD.

Expose these functions to be used by other modules such as a tpm
driver.

Co-developed-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Co-developed-by: Claudio Carvalho <cclaudio@linux.ibm.com>
Signed-off-by: Claudio Carvalho <cclaudio@linux.ibm.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
James, Claudio are you fine with the Cdb, Sob?
The code is pretty much similar to what was in the initial RFC, but I
changed the context for that I reset the author but added C-o-b.
Please, let me know if this is okay or if I need to do anything
else (reset the author, etc.)
---
arch/x86/include/asm/sev.h | 3 +++
arch/x86/coco/sev/core.c | 47 ++++++++++++++++++++++++++++++++++++++
2 files changed, 50 insertions(+)

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index f6ebf4492606..e379bcdddf07 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -485,6 +485,9 @@ void snp_msg_free(struct snp_msg_desc *mdesc);
int snp_send_guest_request(struct snp_msg_desc *mdesc, struct snp_guest_req *req,
struct snp_guest_request_ioctl *rio);

+bool snp_svsm_vtpm_probe(void);
+int snp_svsm_vtpm_send_command(u8 *buffer);
+
void __init snp_secure_tsc_prepare(void);
void __init snp_secure_tsc_init(void);

diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index 82492efc5d94..4158e447d645 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -2628,6 +2628,53 @@ static int snp_issue_guest_request(struct snp_guest_req *req, struct snp_req_dat
return ret;
}

+bool snp_svsm_vtpm_probe(void)
+{
+ struct svsm_call call = {};
+ u64 send_cmd_mask = 0;
+ u64 platform_cmds;
+ u64 features;
+ int ret;
+
+ /* The vTPM device is available only if we have a SVSM */
+ if (!snp_vmpl)
+ return false;
+
+ 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 should be zero */
+ if (features)
+ pr_warn("SNP SVSM vTPM unsupported features: 0x%llx\n",
+ features);
+
+ /* TPM_SEND_COMMAND - platform command 8 */
+ send_cmd_mask = 1 << 8;
+
+ return (platform_cmds & send_cmd_mask) == send_cmd_mask;
+}
+EXPORT_SYMBOL_GPL(snp_svsm_vtpm_probe);
+
+int snp_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);
+}
+EXPORT_SYMBOL_GPL(snp_svsm_vtpm_send_command);
+
static struct platform_device sev_guest_device = {
.name = "sev-guest",
.id = -1,
--
2.48.1