Date:   Tue, 1 Nov 2022 13:53:09 -0300
From:   Wander Lairson Costa <wander@...hat.com>
To:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Shuah Khan <shuah@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        "H . Peter Anvin" <hpa@...or.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Kai Huang <kai.huang@...el.com>,
        Isaku Yamahata <isaku.yamahata@...il.com>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.com,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v16 3/3] selftests: tdx: Test TDX attestation GetReport
 support

On Tue, Nov 01, 2022 at 06:43:31AM -0700, Sathyanarayanan Kuppuswamy wrote:
> 
> 
> On 11/1/22 6:35 AM, Wander Lairson Costa wrote:
> > On Thu, Oct 27, 2022 at 05:28:20PM -0700, Kuppuswamy Sathyanarayanan wrote:
> >> Attestation is used to verify the trustworthiness of a TDX guest.
> >> During the guest bring-up, the Intel TDX module measures and records
> >> the initial contents and configuration of the guest, and at runtime,
> >> guest software uses runtime measurement registers (RMTRs) to measure
> >> and record details related to kernel image, command line params, ACPI
> >> tables, initrd, etc. At guest runtime, the attestation process is used
> >> to attest to these measurements.
> >>
> >> The first step in the TDX attestation process is to get the TDREPORT
> >> data. It is a fixed size data structure generated by the TDX module
> >> which includes the above mentioned measurements data, a MAC ID to
> >> protect the integrity of the TDREPORT, and a 64-Byte of user specified
> >> data passed during TDREPORT request which can uniquely identify the
> >> TDREPORT.
> >>
> >> Intel's TDX guest driver exposes TDX_CMD_GET_REPORT IOCTL interface to
> >> enable guest userspace to get the TDREPORT.
> >>
> >> Add a kernel self test module to test this ABI and verify the validity
> >> of the generated TDREPORT.
> >>
> >> Reviewed-by: Tony Luck <tony.luck@...el.com>
> >> Reviewed-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> >> Acked-by: Kai Huang <kai.huang@...el.com>
> >> Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> >> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> >> ---
> >>
> >> Changes since v15:
> >>  * None
> >>
> >> Changes since v14:
> >>  * Fixed format issue in struct comments.
> >>  * Rebased on top of v6.1-rc1
> >>
> >> Changes since v13:
> >>  * Removed __packed from TDREPORT structs.
> >>  * Since the guest driver is moved to drivers/virt/coco, removed
> >>    tools/arch/x86/include header folder usage.
> >>  * Fixed struct comments to match kernel-doc format.
> >>  * Fixed commit log as per review comments.
> >>  * Fixed some format issues in the code.
> >>
> >> Changes since v12:
> >>  * Changed #ifdef DEBUG usage with if (DEBUG).
> >>  * Initialized reserved entries values to zero.
> >>
> >> Changes since v11:
> >>  * Renamed devname with TDX_GUEST_DEVNAME.
> >>
> >> Changes since v10:
> >>  * Replaced TD/TD Guest usage with guest or TDX guest.
> >>  * Reworded the subject line.
> >>
> >> Changes since v9:
> >>  * Copied arch/x86/include/uapi/asm/tdx.h to tools/arch/x86/include to
> >>    decouple header dependency between kernel source and tools dir.
> >>  * Fixed Makefile to adapt to above change.
> >>  * Fixed commit log and comments.
> >>  * Added __packed to hardware structs.
> >>
> >> Changes since v8:
> >>  * Please refer to https://lore.kernel.org/all/ \
> >>    20220728034420.648314-1-sathyanarayanan.kuppuswamy@...ux.intel.com/
> >>
> >>  tools/testing/selftests/Makefile             |   1 +
> >>  tools/testing/selftests/tdx/Makefile         |   7 +
> >>  tools/testing/selftests/tdx/config           |   1 +
> >>  tools/testing/selftests/tdx/tdx_guest_test.c | 175 +++++++++++++++++++
> >>  4 files changed, 184 insertions(+)
> >>  create mode 100644 tools/testing/selftests/tdx/Makefile
> >>  create mode 100644 tools/testing/selftests/tdx/config
> >>  create mode 100644 tools/testing/selftests/tdx/tdx_guest_test.c
> >>
> >> diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
> >> index 0464b2c6c1e4..f60e14d16bfd 100644
> >> --- a/tools/testing/selftests/Makefile
> >> +++ b/tools/testing/selftests/Makefile
> >> @@ -73,6 +73,7 @@ TARGETS += sync
> >>  TARGETS += syscall_user_dispatch
> >>  TARGETS += sysctl
> >>  TARGETS += tc-testing
> >> +TARGETS += tdx
> >>  TARGETS += timens
> >>  ifneq (1, $(quicktest))
> >>  TARGETS += timers
> >> diff --git a/tools/testing/selftests/tdx/Makefile b/tools/testing/selftests/tdx/Makefile
> >> new file mode 100644
> >> index 000000000000..8dd43517cd55
> >> --- /dev/null
> >> +++ b/tools/testing/selftests/tdx/Makefile
> >> @@ -0,0 +1,7 @@
> >> +# SPDX-License-Identifier: GPL-2.0
> >> +
> >> +CFLAGS += -O3 -Wl,-no-as-needed -Wall -static
> >> +
> >> +TEST_GEN_PROGS := tdx_guest_test
> >> +
> >> +include ../lib.mk
> >> diff --git a/tools/testing/selftests/tdx/config b/tools/testing/selftests/tdx/config
> >> new file mode 100644
> >> index 000000000000..aa1edc829ab6
> >> --- /dev/null
> >> +++ b/tools/testing/selftests/tdx/config
> >> @@ -0,0 +1 @@
> >> +CONFIG_TDX_GUEST_DRIVER=y
> >> diff --git a/tools/testing/selftests/tdx/tdx_guest_test.c b/tools/testing/selftests/tdx/tdx_guest_test.c
> >> new file mode 100644
> >> index 000000000000..a5c243f73adc
> >> --- /dev/null
> >> +++ b/tools/testing/selftests/tdx/tdx_guest_test.c
> >> @@ -0,0 +1,175 @@
> >> +// SPDX-License-Identifier: GPL-2.0
> >> +/*
> >> + * Test TDX guest features
> >> + *
> >> + * Copyright (C) 2022 Intel Corporation.
> >> + *
> >> + * Author: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> >> + */
> >> +
> >> +#include <sys/ioctl.h>
> >> +
> >> +#include <errno.h>
> >> +#include <fcntl.h>
> >> +
> >> +#include "../kselftest_harness.h"
> >> +#include "../../../../include/uapi/linux/tdx-guest.h"
> >> +
> >> +#define TDX_GUEST_DEVNAME "/dev/tdx_guest"
> >> +#define HEX_DUMP_SIZE 8
> >> +#define DEBUG 0
> >> +
> >> +/**
> >> + * struct tdreport_type - Type header of TDREPORT_STRUCT.
> >> + * @type: Type of the TDREPORT (0 - SGX, 81 - TDX, rest are reserved)
> >> + * @sub_type: Subtype of the TDREPORT (Default value is 0).
> >> + * @version: TDREPORT version (Default value is 0).
> >> + * @reserved: Added for future extension.
> >> + *
> >> + * More details can be found in TDX v1.0 module specification, sec
> >> + * titled "REPORTTYPE".
> >> + */
> >> +struct tdreport_type {
> >> +	__u8 type;
> >> +	__u8 sub_type;
> >> +	__u8 version;
> >> +	__u8 reserved;
> >> +};
> >> +
> >> +/**
> >> + * struct reportmac - TDX guest report data, MAC and TEE hashes.
> >> + * @type: TDREPORT type header.
> >> + * @reserved1: Reserved for future extension.
> >> + * @cpu_svn: CPU security version.
> >> + * @tee_tcb_info_hash: SHA384 hash of TEE TCB INFO.
> >> + * @tee_td_info_hash: SHA384 hash of TDINFO_STRUCT.
> >> + * @reportdata: User defined unique data passed in TDG.MR.REPORT request.
> >> + * @reserved2: Reserved for future extension.
> >> + * @mac: CPU MAC ID.
> >> + *
> >> + * It is MAC-protected and contains hashes of the remainder of the
> >> + * report structure along with user provided report data. More details can
> >> + * be found in TDX v1.0 Module specification, sec titled "REPORTMACSTRUCT"
> >> + */
> >> +struct reportmac {
> >> +	struct tdreport_type type;
> >> +	__u8 reserved1[12];
> >> +	__u8 cpu_svn[16];
> >> +	__u8 tee_tcb_info_hash[48];
> >> +	__u8 tee_td_info_hash[48];
> >> +	__u8 reportdata[64];
> >> +	__u8 reserved2[32];
> >> +	__u8 mac[32];
> >> +};
> >> +
> >> +/**
> >> + * struct td_info - TDX guest measurements and configuration.
> >> + * @attr: TDX Guest attributes (like debug, spet_disable, etc).
> >> + * @xfam: Extended features allowed mask.
> >> + * @mrtd: Build time measurement register.
> >> + * @mrconfigid: Software-defined ID for non-owner-defined configuration
> >> + *              of the guest - e.g., run-time or OS configuration.
> >> + * @mrowner: Software-defined ID for the guest owner.
> >> + * @mrownerconfig: Software-defined ID for owner-defined configuration of
> >> + *                 the guest - e.g., specific to the workload.
> >> + * @rtmr: Run time measurement registers.
> >> + * @reserved: Added for future extension.
> >> + *
> >> + * It contains the measurements and initial configuration of the TDX guest
> >> + * that was locked at initialization and a set of measurement registers
> >> + * that are run-time extendable. More details can be found in TDX v1.0
> >> + * Module specification, sec titled "TDINFO_STRUCT".
> >> + */
> >> +struct td_info {
> >> +	__u8 attr[8];
> >> +	__u64 xfam;
> >> +	__u64 mrtd[6];
> >> +	__u64 mrconfigid[6];
> >> +	__u64 mrowner[6];
> >> +	__u64 mrownerconfig[6];
> >> +	__u64 rtmr[24];
> >> +	__u64 reserved[14];
> >> +};
> >> +
> >> +/*
> >> + * struct tdreport - Output of TDCALL[TDG.MR.REPORT].
> >> + * @reportmac: Mac protected header of size 256 bytes.
> >> + * @tee_tcb_info: Additional attestable elements in the TCB are not
> >> + *                reflected in the reportmac.
> >> + * @reserved: Added for future extension.
> >> + * @tdinfo: Measurements and configuration data of size 512 bytes.
> >> + *
> >> + * More details can be found in TDX v1.0 Module specification, sec
> >> + * titled "TDREPORT_STRUCT".
> >> + */
> >> +struct tdreport {
> >> +	struct reportmac reportmac;
> >> +	__u8 tee_tcb_info[239];
> >> +	__u8 reserved[17];
> >> +	struct td_info tdinfo;
> >> +};
> >> +
> >> +static void print_array_hex(const char *title, const char *prefix_str,
> >> +			    const void *buf, int len)
> >> +{
> >> +	int i, j, line_len, rowsize = HEX_DUMP_SIZE;
> >> +	const __u8 *ptr = buf;
> >> +
> >> +	if (!len || !buf)
> > 
> > If len is not zero and buf is null, this would be bug. It is better to
> > let the code crash or assert buf isn't null after testing len.
> 
> It is just a debug dump routine. So I don't think you need to add assert or
> crash here. If you really want some indication, maybe we can add an error message
> for invalid params.

Honestly, by design the code never enters in the `if` condition. So I am
in favor of removing it.

> 
> > 
> 
> -- 
> Sathyanarayanan Kuppuswamy
> Linux Kernel Developer
> 

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