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From: Stefano Garzarella <sgarzare@redhat.com>
To: Jarkko Sakkinen <jarkko@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
Peter Huewe <peterhuewe@gmx.de>,
Jason Gunthorpe <jgg@ziepe.ca>,
"H. Peter Anvin" <hpa@zytor.com>,
linux-coco@lists.linux.dev,
linux-integrity@vger.kernel.org,
Borislav Petkov <bp@alien8.de>,
Ingo Molnar <mingo@redhat.com>,
x86@kernel.org,
Tom Lendacky <thomas.lendacky@amd.com>,
Joerg Roedel <jroedel@suse.de>,
Dionna Glaze <dionnaglaze@google.com>,
Claudio Carvalho <cclaudio@linux.ibm.com>,
James Bottomley <James.Bottomley@HansenPartnership.com>,
linux-kernel@vger.kernel.org,
Dov Murik <dovmurik@linux.ibm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Stefano Garzarella <sgarzare@redhat.com>
Subject: [PATCH v6 1/4] x86/sev: add SVSM vTPM probe/send_command functions
Date: Thu, 3 Apr 2025 12:09:39 +0200
Message-ID: <20250403100943.120738-2-sgarzare@redhat.com>
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From: Stefano Garzarella <sgarzare@redhat.com>
Add two new functions to probe and send commands to the SVSM vTPM.
They leverage the two calls defined by the AMD SVSM specification [1]
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.
[1] "Secure VM Service Module for SEV-SNP Guests"
Publication # 58019 Revision: 1.00
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>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
v5:
- added stubs when !CONFIG_AMD_MEM_ENCRYPT [Dionna]
- added Jarkko's R-b
v4:
- added Tom's R-b
- added functions documentation [Jarkko]
- simplified TPM_SEND_COMMAND check [Tom/Jarkko]
v3:
- removed link to the spec because those URLs are unstable [Borislav]
- squashed "x86/sev: add SVSM call macros for the vTPM protocol" patch
in this one [Borislav]
- slimmed down snp_svsm_vtpm_probe() [Borislav]
- removed features check and any print related [Tom]
---
arch/x86/include/asm/sev.h | 9 ++++++
arch/x86/coco/sev/core.c | 59 ++++++++++++++++++++++++++++++++++++++
2 files changed, 68 insertions(+)
diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index ba7999f66abe..ba7a0a327afb 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -384,6 +384,10 @@ struct svsm_call {
#define SVSM_ATTEST_SERVICES 0
#define SVSM_ATTEST_SINGLE_SERVICE 1
=20
+#define SVSM_VTPM_CALL(x) ((2ULL << 32) | (x))
+#define SVSM_VTPM_QUERY 0
+#define SVSM_VTPM_CMD 1
+
#ifdef CONFIG_AMD_MEM_ENCRYPT
=20
extern u8 snp_vmpl;
@@ -481,6 +485,9 @@ void snp_msg_free(struct snp_msg_desc *mdesc);
int snp_send_guest_request(struct snp_msg_desc *mdesc, struct snp_guest_re=
q *req,
struct snp_guest_request_ioctl *rio);
=20
+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);
=20
@@ -524,6 +531,8 @@ static inline struct snp_msg_desc *snp_msg_alloc(void) =
{ return NULL; }
static inline void snp_msg_free(struct snp_msg_desc *mdesc) { }
static inline int snp_send_guest_request(struct snp_msg_desc *mdesc, struc=
t snp_guest_req *req,
struct snp_guest_request_ioctl *rio) { return -ENODEV; }
+static inline bool snp_svsm_vtpm_probe(void) { return false; }
+static inline int snp_svsm_vtpm_send_command(u8 *buffer) { return -ENODEV;=
}
static inline void __init snp_secure_tsc_prepare(void) { }
static inline void __init snp_secure_tsc_init(void) { }
=20
diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index b0c1a7a57497..efb43c9d3d30 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -2625,6 +2625,65 @@ static int snp_issue_guest_request(struct snp_guest_=
req *req, struct snp_req_dat
return ret;
}
=20
+/**
+ * snp_svsm_vtpm_probe() - Probe if SVSM provides a vTPM device
+ *
+ * This function checks that there is SVSM and that it supports at least
+ * TPM_SEND_COMMAND which is the only request we use so far.
+ *
+ * Return: true if the platform provides a vTPM SVSM device, false otherwi=
se.
+ */
+bool snp_svsm_vtpm_probe(void)
+{
+ struct svsm_call call =3D {};
+
+ /* The vTPM device is available only if a SVSM is present */
+ if (!snp_vmpl)
+ return false;
+
+ call.caa =3D svsm_get_caa();
+ call.rax =3D SVSM_VTPM_CALL(SVSM_VTPM_QUERY);
+
+ if (svsm_perform_call_protocol(&call))
+ return false;
+
+ /* Check platform commands contains TPM_SEND_COMMAND - platform command 8=
*/
+ return call.rcx_out & BIT_ULL(8);
+}
+EXPORT_SYMBOL_GPL(snp_svsm_vtpm_probe);
+
+/**
+ * snp_svsm_vtpm_send_command() - execute a vTPM operation on SVSM
+ * @buffer: A buffer used to both send the command and receive the respons=
e.
+ *
+ * This function executes a SVSM_VTPM_CMD call as defined by
+ * "Secure VM Service Module for SEV-SNP Guests" Publication # 58019 Revis=
ion: 1.00
+ *
+ * All command request/response buffers have a common structure as specifi=
ed by
+ * the following table:
+ * Byte Size =C2=A0=C2=A0 =C2=A0In/Out=C2=A0=C2=A0=C2=A0=C2=A0D=
escription
+ * Offset=C2=A0=C2=A0=C2=A0=C2=A0(Bytes)
+ * 0x000=C2=A0=C2=A0=C2=A0=C2=A0=C2=A04=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0In=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0Platform command
+=C2=A0*=C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0Out=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0Platform command respons=
e size
+ *
+ * Each command can build upon this common request/response structure to c=
reate
+ * a structure specific to the command.
+ * See include/linux/tpm_svsm.h for more details.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int snp_svsm_vtpm_send_command(u8 *buffer)
+{
+ struct svsm_call call =3D {};
+
+ call.caa =3D svsm_get_caa();
+ call.rax =3D SVSM_VTPM_CALL(SVSM_VTPM_CMD);
+ call.rcx =3D __pa(buffer);
+
+ return svsm_perform_call_protocol(&call);
+}
+EXPORT_SYMBOL_GPL(snp_svsm_vtpm_send_command);
+
static struct platform_device sev_guest_device =3D {
.name =3D "sev-guest",
.id =3D -1,
--=20
2.49.0