[PATCH v3 2/4] x86/tdx: Add tdx_hcall_get_quote() API support

[Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>]

Attestation is the process used by two un-trusted entities to prove to
each other that it can be trusted. In TDX guest, attestation is mainly
used to verify the trustworthiness of a TD to the 3rd party key
servers.

First step in the attestation process is to generate the TDREPORT data.
This support is added using tdx_mcall_tdreport() API. The second stage
in the attestation process is for the guest to request the VMM generate
and sign a quote based on the TDREPORT acquired earlier. More details
about the steps involved in attestation process can be found in TDX
Guest-Host Communication Interface (GHCI) for Intel TDX 1.5, section
titled "TD attestation"

Add tdx_hcall_get_quote() helper function to implement the GetQuote
hypercall.

More details about the GetQuote TDVMCALL are in the Guest-Host
Communication Interface (GHCI) Specification, sec 3.3, titled
"VP.VMCALL<GetQuote>".

This will be used by the TD attestation driver in follow-on patches.

Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
---
 arch/x86/coco/tdx/tdx.c    | 38 ++++++++++++++++++++++++++++++++++++++
 arch/x86/include/asm/tdx.h |  2 ++
 2 files changed, 40 insertions(+)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 3e409b618d3f..c259d81a5d7f 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -21,6 +21,7 @@
 
 /* TDX hypercall Leaf IDs */
 #define TDVMCALL_MAP_GPA		0x10001
+#define TDVMCALL_GET_QUOTE		0x10002
 
 /* MMIO direction */
 #define EPT_READ	0
@@ -144,6 +145,43 @@ long tdx_mcall_tdreport(void *data, void *reportdata)
 }
 EXPORT_SYMBOL_GPL(tdx_mcall_tdreport);
 
+/*
+ * tdx_hcall_get_quote() - Generate TDQUOTE using TDREPORT_STRUCT.
+ *
+ * @data        : Address of 8KB GPA memory which contains
+ *                TDREPORT_STRUCT.
+ * @len		: Length of the GPA in bytes.
+ *
+ * return 0 on success or failure error number.
+ */
+long tdx_hcall_get_quote(void *data, u64 len)
+{
+	u64 ret;
+
+	/*
+	 * Use confidential guest TDX check to ensure this API is only
+	 * used by TDX guest platforms.
+	 */
+	if (!data || !cpu_feature_enabled(X86_FEATURE_TDX_GUEST))
+		return -EINVAL;
+
+	/*
+	 * Pass the physical address of tdreport data to the VMM
+	 * and trigger the tdquote generation. Quote data will be
+	 * stored back in the same physical address space. More info
+	 * about ABI can be found in TDX Guest-Host-Communication
+	 * Interface (GHCI), sec titled "TDG.VP.VMCALL<GetQuote>".
+	 */
+	ret = _tdx_hypercall(TDVMCALL_GET_QUOTE, cc_mkdec(virt_to_phys(data)),
+			     len, 0, 0);
+
+	if (ret)
+		return ret;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(tdx_hcall_get_quote);
+
 static u64 get_cc_mask(void)
 {
 	struct tdx_module_output out;
diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index a151f69dd6ef..014cc6192dc5 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -69,6 +69,8 @@ bool tdx_early_handle_ve(struct pt_regs *regs);
 
 long tdx_mcall_tdreport(void *data, void *reportdata);
 
+long tdx_hcall_get_quote(void *data, u64 len);
+
 #else
 
 static inline void tdx_early_init(void) { };
-- 
2.25.1