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

Edgecombe, Rick P
2025-01-03T18:03:05Z

On Wed, 2025-01-01 at 02:49 -0500, Paolo Bonzini wrote:
> 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)

gpa should be type gpa_t to avoid bare u64 types.

> +{
> + 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;

Could be extended_err1/2.

> +
> + 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