[PATCH 3/4] x86/tdx: Add tdx_mcall_rtmr_extend() interface

[Cedric Xing <cedric.xing@intel.com>]

From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

The TDX guest exposes one MRTD (Build-time Measurement Register) and
three 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.

Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
---
 arch/x86/coco/tdx/tdx.c           | 36 ++++++++++++++++++++++++++++++++++++
 arch/x86/include/asm/shared/tdx.h |  1 +
 arch/x86/include/asm/tdx.h        |  2 ++
 3 files changed, 39 insertions(+)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 32809a06dab4..9267fffecbef 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -35,6 +35,7 @@
 /* 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
 
@@ -135,6 +136,41 @@ int tdx_mcall_get_report0(u8 *reportdata, u8 *tdreport)
 }
 EXPORT_SYMBOL_GPL(tdx_mcall_get_report0);
 
+/**
+ * tdx_mcall_rtmr_extend() - 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 extend the
+ * RTMR registers (index > 1).
+ *
+ * Return 0 on success, -EINVAL for invalid operands, -EBUSY for busy
+ * operation or -EIO on other TDCALL failures.
+ */
+int tdx_mcall_rtmr_extend(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 -EINVAL;
+		if (TDCALL_RETURN_CODE(ret) == TDCALL_OPERAND_BUSY)
+			return -EBUSY;
+		return -EIO;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(tdx_mcall_rtmr_extend);
+
 /**
  * tdx_hcall_get_quote() - Wrapper to request TD Quote using GetQuote
  *                         hypercall.
diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h
index fcbbef484a78..7b95c3113e79 100644
--- a/arch/x86/include/asm/shared/tdx.h
+++ b/arch/x86/include/asm/shared/tdx.h
@@ -12,6 +12,7 @@
 
 /* TDX module Call Leaf IDs */
 #define TDG_VP_VMCALL			0
+#define TDG_MR_RTMR_EXTEND		2
 #define TDG_VP_INFO			1
 #define TDG_VP_VEINFO_GET		3
 #define TDG_MR_REPORT			4
diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index b4b16dafd55e..6c73ab759223 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/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_rtmr_extend(u8 index, u8 *data);
+
 u64 tdx_hcall_get_quote(u8 *buf, size_t size);
 
 void __init tdx_dump_attributes(u64 td_attr);

-- 
2.43.0