x86/tdx: Add tdx_mcall_extend_rtmr() interface

The TDX guest exposes one MRTD (Build-time Measurement Register) and four
RTMR (Run-time Measurement Register) registers to record the build and boot
measurements of a virtual machine (VM). These registers are similar to PCR
(Platform Configuration Register) registers in the TPM (Trusted Platform
Module) space. This measurement data is used to implement security features
like attestation and trusted boot.

To facilitate updating the RTMR registers, the TDX module provides support
for the `TDG.MR.RTMR.EXTEND` TDCALL which can be used to securely extend
the RTMR registers.

Add helper function to update RTMR registers. It will be used by the TDX
guest driver in enabling RTMR extension support.

Co-developed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: Cedric Xing <cedric.xing@intel.com>
Acked-by: Dionna Amalie Glaze <dionnaglaze@google.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://patch.msgid.link/20250506-tdx-rtmr-v6-3-ac6ff5e9d58a@intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

arch/x86/coco/tdx/tdx.c

@@ -36,6 +36,7 @@
 /* TDX Module call error codes */
 #define TDCALL_RETURN_CODE(a)	((a) >> 32)
 #define TDCALL_INVALID_OPERAND	0xc0000100
+#define TDCALL_OPERAND_BUSY	0x80000200
 
 #define TDREPORT_SUBTYPE_0	0
 
@@ -136,6 +137,42 @@ int tdx_mcall_get_report0(u8 *reportdata, u8 *tdreport)
 }
 EXPORT_SYMBOL_GPL(tdx_mcall_get_report0);
 
+/**
+ * tdx_mcall_extend_rtmr() - Wrapper to extend RTMR registers using
+ *			     TDG.MR.RTMR.EXTEND TDCALL.
+ * @index: Index of RTMR register to be extended.
+ * @data: Address of the input buffer with RTMR register extend data.
+ *
+ * Refer to section titled "TDG.MR.RTMR.EXTEND leaf" in the TDX Module v1.0
+ * specification for more information on TDG.MR.RTMR.EXTEND TDCALL.
+ *
+ * It is used in the TDX guest driver module to allow user to extend the RTMR
+ * registers.
+ *
+ * Return 0 on success, -ENXIO for invalid operands, -EBUSY for busy operation,
+ * or -EIO on other TDCALL failures.
+ */
+int tdx_mcall_extend_rtmr(u8 index, u8 *data)
+{
+	struct tdx_module_args args = {
+		.rcx = virt_to_phys(data),
+		.rdx = index,
+	};
+	u64 ret;
+
+	ret = __tdcall(TDG_MR_RTMR_EXTEND, &args);
+	if (ret) {
+		if (TDCALL_RETURN_CODE(ret) == TDCALL_INVALID_OPERAND)
+			return -ENXIO;
+		if (TDCALL_RETURN_CODE(ret) == TDCALL_OPERAND_BUSY)
+			return -EBUSY;
+		return -EIO;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(tdx_mcall_extend_rtmr);
+
 /**
  * tdx_hcall_get_quote() - Wrapper to request TD Quote using GetQuote
  *                         hypercall.

arch/x86/include/asm/shared/tdx.h

@@ -13,6 +13,7 @@
 /* TDX module Call Leaf IDs */
 #define TDG_VP_VMCALL			0
 #define TDG_VP_INFO			1
+#define TDG_MR_RTMR_EXTEND		2
 #define TDG_VP_VEINFO_GET		3
 #define TDG_MR_REPORT			4
 #define TDG_MEM_PAGE_ACCEPT		6

arch/x86/include/asm/tdx.h

@@ -64,6 +64,8 @@ bool tdx_early_handle_ve(struct pt_regs *regs);
 
 int tdx_mcall_get_report0(u8 *reportdata, u8 *tdreport);
 
+int tdx_mcall_extend_rtmr(u8 index, u8 *data);
+
 u64 tdx_hcall_get_quote(u8 *buf, size_t size);
 
 void __init tdx_dump_attributes(u64 td_attr);