[PATCH 11/13] x86/virt/tdx: Add SEAMCALL wrappers for TD measurement of initial contents

Paolo Bonzini
2025-01-01T07:50:26Z

From: Isaku Yamahata <isaku.yamahata@intel.com>

The TDX module measures the TD during the build process and saves the
measurement in TDCS.MRTD to facilitate TD attestation of the initial
contents of the TD. Wrap the SEAMCALL TDH.MR.EXTEND with tdh_mr_extend()
and TDH.MR.FINALIZE with tdh_mr_finalize() to enable the host kernel to
assist the TDX module in performing the measurement.

The measurement in TDCS.MRTD is a SHA-384 digest of the build process.
SEAMCALLs TDH.MNG.INIT and TDH.MEM.PAGE.ADD initialize and contribute to
the MRTD digest calculation.

The caller of tdh_mr_extend() should break the TD private page into chunks
of size TDX_EXTENDMR_CHUNKSIZE and invoke tdh_mr_extend() to add the page
content into the digest calculation. Failures are possible with
TDH.MR.EXTEND (e.g., due to SEPT walking). The caller of tdh_mr_extend()
can check the function return value and retrieve extended error information
from the function output parameters.

Calling tdh_mr_finalize() completes the measurement. The TDX module then
turns the TD into the runnable state. Further TDH.MEM.PAGE.ADD and
TDH.MR.EXTEND calls will fail.

TDH.MR.FINALIZE may fail due to errors such as the TD having no vCPUs or
contentions. Check function return value when calling tdh_mr_finalize() to
determine the exact reason for failure. Take proper locks on the caller's
side to avoid contention failures, or handle the BUSY error in specific
ways (e.g., retry). Return the SEAMCALL error code directly to the caller.
Do not attempt to handle it in the core kernel.

[Kai: Switched from generic seamcall export]
[Yan: Re-wrote the changelog]
Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Signed-off-by: Kai Huang <kai.huang@intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
Message-ID: <20241112073709.22171-1-yan.y.zhao@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/include/asm/tdx.h | 2 ++
arch/x86/virt/vmx/tdx/tdx.c | 27 +++++++++++++++++++++++++++
arch/x86/virt/vmx/tdx/tdx.h | 2 ++
3 files changed, 31 insertions(+)

diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index 74938f725481..6981a3d75eb2 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -147,6 +147,8 @@ u64 tdh_mng_key_config(struct tdx_td *td);
u64 tdh_mng_create(struct tdx_td *td, u64 hkid);
u64 tdh_vp_create(struct tdx_td *td, struct tdx_vp *vp);
u64 tdh_mng_rd(struct tdx_td *td, u64 field, u64 *data);
+u64 tdh_mr_extend(struct tdx_td *td, u64 gpa, u64 *rcx, u64 *rdx);
+u64 tdh_mr_finalize(struct tdx_td *td);
u64 tdh_vp_flush(struct tdx_vp *vp);
u64 tdh_mng_vpflushdone(struct tdx_td *td);
u64 tdh_mng_key_freeid(struct tdx_td *td);
diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index cde55e9b3280..84fe5bc79434 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -1629,6 +1629,33 @@ u64 tdh_mng_rd(struct tdx_td *td, u64 field, u64 *data)
}
EXPORT_SYMBOL_GPL(tdh_mng_rd);

+u64 tdh_mr_extend(struct tdx_td *td, u64 gpa, u64 *rcx, u64 *rdx)
+{
+ struct tdx_module_args args = {
+ .rcx = gpa,
+ .rdx = tdx_tdr_pa(td),
+ };
+ u64 ret;
+
+ ret = seamcall_ret(TDH_MR_EXTEND, &args);
+
+ *rcx = args.rcx;
+ *rdx = args.rdx;
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(tdh_mr_extend);
+
+u64 tdh_mr_finalize(struct tdx_td *td)
+{
+ struct tdx_module_args args = {
+ .rcx = tdx_tdr_pa(td),
+ };
+
+ return seamcall(TDH_MR_FINALIZE, &args);
+}
+EXPORT_SYMBOL_GPL(tdh_mr_finalize);
+
u64 tdh_vp_flush(struct tdx_vp *vp)
{
struct tdx_module_args args = {
diff --git a/arch/x86/virt/vmx/tdx/tdx.h b/arch/x86/virt/vmx/tdx/tdx.h
index d49cdd9b0577..a1e34773bab7 100644
--- a/arch/x86/virt/vmx/tdx/tdx.h
+++ b/arch/x86/virt/vmx/tdx/tdx.h
@@ -24,6 +24,8 @@
#define TDH_MNG_KEY_CONFIG 8
#define TDH_MNG_CREATE 9
#define TDH_MNG_RD 11
+#define TDH_MR_EXTEND 16
+#define TDH_MR_FINALIZE 17
#define TDH_VP_FLUSH 18
#define TDH_MNG_VPFLUSHDONE 19
#define TDH_VP_CREATE 10
--
2.43.5