[PATCH v9 0/6] Add TDX Guest Attestation support

Kuppuswamy Sathyanarayanan
2022-07-28T03:44:34Z

Hi All,

Intel's Trust Domain Extensions (TDX) protect guest VMs from malicious
hosts and some physical attacks. VM guest with TDX support is called
as TD Guest.

In TD Guest, the attestation process is used to verify the
trustworthiness of TD guest to the 3rd party servers. Such attestation
process is required by 3rd party servers before sending sensitive
information to TD guests. One usage example is to get encryption keys
from the key server for mounting the encrypted rootfs or secondary drive.

During TD launch, the initial contents and configuration of the TD are
recorded by the Intel TDX module in the build time measurement register
(MRTD). In addition, run-time measurement registers (RTMRs) can be
used by the guest TD software, e.g., to measure a boot process. At
run-time, the Intel TDX module reuses the Intel SGX attestation
infrastructure to provide support for attesting to these measurements
as described below.

Intel TDX attestation is intended to be used in two phases:

TD Guest can use the TDCALL(TDG.MR.REPORT) function to request the
Intel TDX Module to generate an integrity-protected TDREPORT structure
(TDREPORT_STRUCT). This structure includes the TD’s measurements, the
Intel TDX module’s measurements, and a value provided by the guest TD
software. This will typically be an asymmetric key that the attestation
verifier can use to establish a secure channel or protect sensitive
data to be sent to the TD software.

To protect the integrity of TDREPORT_STRUCT, it is HMAC'ed using an
HMAC key which by design can only be verified on the local platform via
the SGX ENCLU(EVERIFYREPORT2) instruction. So to create a remotely
verifiable attestation, the TDREPORT_STRUCT should be converted into a
Quote signed by a certified Quote signing key.

An Intel SGX Quoting Enclave (QE), written specifically to support
quoting Intel TDX TDs, uses EVERIFYREPORT2, to help check the integrity
of the TDG.MR.REPORT. If it passes, the QE can use a certified quote
signing key to sign a quote containing the guest TD’s measurements and
the additional data being quoted.

Method of sending the TDREPORT to QE and to get the Quote depends on
the implementation and deployment of QE. For quote requests from the
guest user space, communication models like vsock or TCP/IP can be
used to get the Quote from QE. But for requests generated during
pre-boot time, since such communication methods may not be available,
QEs at basic had to support GetQuote hypercall model. To keep the
attestation communication protocol same during pre-boot and
post-boot time, some QEs may just opt only to support GetQuote
hypercall request model. So add support to allow guest TD user space
get the Quote using GetQuote hypercall.

Since the Quote generation involves communication with QE, the response
time cannot be accurately defined and is generally long. So to let the TD
guest not wait for the response, host VMM supports callback event
notification via an interrupt vector. This can be used by the host to
notify the TD regarding the completion of the Quote request.

Following patches add the attestation support to the TDX guest which
includes attestation user interface driver, related hypercall
support and self test modules.

Patch 1-2/6 -> Adds TDREPORT support and related selftest.
Patch 3/6 -> Adds event notification IRQ support
Patch 4/6 -> Adds cc_decrypted_alloc/free() support
Patch 5-6/6 -> Adds Quote generation support and related selftest.

Any distribution enabling TDX is also expected to need attestation. So
enable it by default with TDX guest support. The compiled size is
quite small (~500 bytes).

Changes since v8:
* To keep the interface generic to TDX guest, changed interface device
name from tdx-attest -> tdx-guest. Also moved interface device creation
logic from attest.c -> tdx.c.
* Converted test app into self test module as per review suggestion.
* Added subtype and length parameters to tdx_report_req ABI.
* Regarding event notification IRQ, changed static IRQ vector
reservation to runtime model.
* For quote generation shared buffer allocation, replace vmap based
allocation with DMA wrappers (cc_decrypted_alloc/free()).
* Fixed commit log as per review comments.

Changes since v7:
* Removed exports symbols for tdx_setup_ev_notify_handler() and
tdx_remove_ev_notify_handler().
* Changed "struct quote_buf *buf" member in "struct quote_entry"
from pointer to embed object.
* Rebased on top of v5.19-rc1.

Changes since v6:
* Fixed race between wait_for_completion_*() and
quote_callback_handler() in tdx_get_quote() when user terminates the
request.
* Fixed commit log and comments.

Changes since v5:
* Added support for parallel GetQuote requests.
* Add noalias variants of set_memory_*crypted() functions to
changes page attribute without touching direct map.
* Made set_memory_*crypted() functions vmalloc address compatible.
* Use vmap()/set_memory_*crypted() functions to share/unshare
memory without touching the direct map.
* Add support to let driver handle the memory cleanup for the
early termination of user requests.
* Removed unused headers in attest.c
* Fixed commit log and comments as per review comments.

Changes since v4:
* Removed platform driver model in attestation driver and used
miscdevice and initcall approach.
* Since dma_alloc*() APIs require a valid device reference,
replaced it with __get_free_pages() and set_memory_decrypted()
for quote memory allocation.
* Removed tdx_mcall_tdreport() and moved TDG.MR.REPORT TDCALL code
to tdx_get_report().
* Used kmalloc() for TDREPORT memory allocation instead of
get_zeroed_page().
* Returned -EINVAL in default case of tdx_attest_ioctl().
* Added struct tdx_report_req to explicitly mention the
TDX_CMD_GET_REPORT IOCTL argument.
* Removed tdx_get_quote_hypercall() and moved hypercall code to
attestation driver itself.
* Removed GetQuote timeout support (since it is not defined in
spec)
* Added support to check for spurious callback interrupt in GetQuote
request.
* Fixed commit log and comments as per review suggestions.

Changes since v3:
* Moved the attestation driver from platform/x86 to arch/x86/coco/tdx/ and
renamed intel_tdx_attest.c to attest.c.
* Dropped CONFIG_INTEL_TDX_ATTESTATION and added support to compile
attestation changes with CONFIG_INTEL_TDX_GUEST option.
* Merged patch titled "x86/tdx: Add tdx_mcall_tdreport() API support" and
"platform/x86: intel_tdx_attest: Add TDX Guest attestation interface" into
a single patch.
* Moved GetQuote IOCTL support changes from patch titled "platform/x86:
intel_tdx_attest: Add TDX Guest attestation interface driver" to a
separate patch.
* Removed 8K size restriction when requesting quote, and added support
to let userspace decide the quote size.
* Added support to allow attestation agent configure quote generation
timeout value.
* Fixed commit log and comments as per review comments.

Changes since v2:
* As per Han's suggestion, modified the attestation driver to use
platform device driver model.
* Modified tdx_hcall_get_quote() and tdx_mcall_tdreport() APIs to
return TDCALL error code instead of generic error info (like -EIO).
* Removed attestation test app patch from this series to simplify
the patchset and review process. Test app patches will be submitted
once attestation support patches are merged.
* Since patches titled "x86/tdx: Add SetupEventNotifyInterrupt TDX
hypercall support" and "x86/tdx: Add TDX Guest event notify
interrupt vector support" are related, combining them into a
single patch.

Changes since v1:
* Moved test driver from "tools/tdx/attest/tdx-attest-test.c" to
"tools/arch/x86/tdx/attest/tdx-attest-test.c" as per Hans review
suggestion.
* Minor commit log and comment fixes in patches titled
"x86/tdx: Add tdx_mcall_tdreport() API support" and "x86/tdx:
Add tdx_hcall_get_quote() API support"
* Extended tdx_hcall_get_quote() API to accept GPA length as argument
to accomodate latest TDQUOTE TDVMCALL related specification update.
* Added support for tdx_setup_ev_notify_handler() and
tdx_remove_ev_notify_handler() in patch titled "x86/tdx: Add TDX
Guest event notify interrupt vector support"

Kuppuswamy Sathyanarayanan (6):
x86/tdx: Add TDX Guest attestation interface driver
selftests: tdx: Test GetReport TDX attestation feature
x86/tdx: Add TDX Guest event notify interrupt support
x86/coco: Add cc_decrypted_alloc/free() interfaces
x86/tdx: Add Quote generation support
selftests: tdx: Test GetQuote TDX attestation feature

arch/x86/coco/Makefile | 2 +-
arch/x86/coco/mem.c | 90 +++++
arch/x86/coco/tdx/Makefile | 2 +-
arch/x86/coco/tdx/attest.c | 363 ++++++++++++++++++
arch/x86/coco/tdx/tdx.c | 149 +++++++
arch/x86/coco/tdx/tdx.h | 11 +
arch/x86/include/asm/coco.h | 10 +
arch/x86/include/asm/tdx.h | 2 +
arch/x86/include/uapi/asm/tdx.h | 96 +++++
tools/testing/selftests/Makefile | 1 +
tools/testing/selftests/tdx/Makefile | 7 +
tools/testing/selftests/tdx/tdx_attest_test.c | 214 +++++++++++
12 files changed, 945 insertions(+), 2 deletions(-)
create mode 100644 arch/x86/coco/mem.c
create mode 100644 arch/x86/coco/tdx/attest.c
create mode 100644 arch/x86/coco/tdx/tdx.h
create mode 100644 arch/x86/include/uapi/asm/tdx.h
create mode 100644 tools/testing/selftests/tdx/Makefile
create mode 100644 tools/testing/selftests/tdx/tdx_attest_test.c

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2.25.1