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Date:   Wed, 27 Apr 2022 15:15:08 -0700
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Subject: Re: [PATCH v3 09/21] x86/virt/tdx: Get information about TDX module
 and convertible memory
Content-Language: en-US
To:     Kai Huang <kai.huang@intel.com>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     seanjc@google.com, pbonzini@redhat.com, len.brown@intel.com,
        tony.luck@intel.com, rafael.j.wysocki@intel.com,
        reinette.chatre@intel.com, dan.j.williams@intel.com,
        peterz@infradead.org, ak@linux.intel.com,
        kirill.shutemov@linux.intel.com,
        sathyanarayanan.kuppuswamy@linux.intel.com,
        isaku.yamahata@intel.com
References: <cover.1649219184.git.kai.huang@intel.com>
 <145620795852bf24ba2124a3f8234fd4aaac19d4.1649219184.git.kai.huang@intel.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <145620795852bf24ba2124a3f8234fd4aaac19d4.1649219184.git.kai.huang@intel.com>
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On 4/5/22 21:49, Kai Huang wrote:
> TDX provides increased levels of memory confidentiality and integrity.
> This requires special hardware support for features like memory
> encryption and storage of memory integrity checksums.  Not all memory
> satisfies these requirements.
> 
> As a result, TDX introduced the concept of a "Convertible Memory Region"
> (CMR).  During boot, the firmware builds a list of all of the memory
> ranges which can provide the TDX security guarantees.  The list of these
> ranges, along with TDX module information, is available to the kernel by
> querying the TDX module via TDH.SYS.INFO SEAMCALL.
> 
> Host kernel can choose whether or not to use all convertible memory
> regions as TDX memory.  Before TDX module is ready to create any TD
> guests, all TDX memory regions that host kernel intends to use must be
> configured to the TDX module, using specific data structures defined by
> TDX architecture.  Constructing those structures requires information of
> both TDX module and the Convertible Memory Regions.  Call TDH.SYS.INFO
> to get this information as preparation to construct those structures.
> 
> Signed-off-by: Kai Huang <kai.huang@intel.com>
> ---
>  arch/x86/virt/vmx/tdx/tdx.c | 131 ++++++++++++++++++++++++++++++++++++
>  arch/x86/virt/vmx/tdx/tdx.h |  61 +++++++++++++++++
>  2 files changed, 192 insertions(+)
> 
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index ef2718423f0f..482e6d858181 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -80,6 +80,11 @@ static DEFINE_MUTEX(tdx_module_lock);
>  
>  static struct p_seamldr_info p_seamldr_info;
>  
> +/* Base address of CMR array needs to be 512 bytes aligned. */
> +static struct cmr_info tdx_cmr_array[MAX_CMRS] __aligned(CMR_INFO_ARRAY_ALIGNMENT);
> +static int tdx_cmr_num;
> +static struct tdsysinfo_struct tdx_sysinfo;

I really dislike mixing hardware and software structures.  Please make
it clear which of these are fully software-defined and which are part of
the hardware ABI.

>  static bool __seamrr_enabled(void)
>  {
>  	return (seamrr_mask & SEAMRR_ENABLED_BITS) == SEAMRR_ENABLED_BITS;
> @@ -468,6 +473,127 @@ static int tdx_module_init_cpus(void)
>  	return seamcall_on_each_cpu(&sc);
>  }
>  
> +static inline bool cmr_valid(struct cmr_info *cmr)
> +{
> +	return !!cmr->size;
> +}
> +
> +static void print_cmrs(struct cmr_info *cmr_array, int cmr_num,
> +		       const char *name)
> +{
> +	int i;
> +
> +	for (i = 0; i < cmr_num; i++) {
> +		struct cmr_info *cmr = &cmr_array[i];
> +
> +		pr_info("%s : [0x%llx, 0x%llx)\n", name,
> +				cmr->base, cmr->base + cmr->size);
> +	}
> +}
> +
> +static int sanitize_cmrs(struct cmr_info *cmr_array, int cmr_num)
> +{
> +	int i, j;
> +
> +	/*
> +	 * Intel TDX module spec, 20.7.3 CMR_INFO:
> +	 *
> +	 *   TDH.SYS.INFO leaf function returns a MAX_CMRS (32) entry
> +	 *   array of CMR_INFO entries. The CMRs are sorted from the
> +	 *   lowest base address to the highest base address, and they
> +	 *   are non-overlapping.
> +	 *
> +	 * This implies that BIOS may generate invalid empty entries
> +	 * if total CMRs are less than 32.  Skip them manually.
> +	 */
> +	for (i = 0; i < cmr_num; i++) {
> +		struct cmr_info *cmr = &cmr_array[i];
> +		struct cmr_info *prev_cmr = NULL;
> +
> +		/* Skip further invalid CMRs */
> +		if (!cmr_valid(cmr))
> +			break;
> +
> +		if (i > 0)
> +			prev_cmr = &cmr_array[i - 1];
> +
> +		/*
> +		 * It is a TDX firmware bug if CMRs are not
> +		 * in address ascending order.
> +		 */
> +		if (prev_cmr && ((prev_cmr->base + prev_cmr->size) >
> +					cmr->base)) {
> +			pr_err("Firmware bug: CMRs not in address ascending order.\n");
> +			return -EFAULT;

-EFAULT is a really weird return code to use for this.  I'd use -EINVAL.

> +		}
> +	}
> +
> +	/*
> +	 * Also a sane BIOS should never generate invalid CMR(s) between
> +	 * two valid CMRs.  Sanity check this and simply return error in
> +	 * this case.
> +	 *
> +	 * By reaching here @i is the index of the first invalid CMR (or
> +	 * cmr_num).  Starting with next entry of @i since it has already
> +	 * been checked.
> +	 */
> +	for (j = i + 1; j < cmr_num; j++)
> +		if (cmr_valid(&cmr_array[j])) {
> +			pr_err("Firmware bug: invalid CMR(s) among valid CMRs.\n");
> +			return -EFAULT;
> +		}

Please add brackets for the for().

> +	/*
> +	 * Trim all tail invalid empty CMRs.  BIOS should generate at
> +	 * least one valid CMR, otherwise it's a TDX firmware bug.
> +	 */
> +	tdx_cmr_num = i;
> +	if (!tdx_cmr_num) {
> +		pr_err("Firmware bug: No valid CMR.\n");
> +		return -EFAULT;
> +	}
> +
> +	/* Print kernel sanitized CMRs */
> +	print_cmrs(tdx_cmr_array, tdx_cmr_num, "Kernel-sanitized-CMR");
> +
> +	return 0;
> +}
> +
> +static int tdx_get_sysinfo(void)
> +{
> +	struct tdx_module_output out;
> +	u64 tdsysinfo_sz, cmr_num;
> +	int ret;
> +
> +	BUILD_BUG_ON(sizeof(struct tdsysinfo_struct) != TDSYSINFO_STRUCT_SIZE);
> +
> +	ret = seamcall(TDH_SYS_INFO, __pa(&tdx_sysinfo), TDSYSINFO_STRUCT_SIZE,
> +			__pa(tdx_cmr_array), MAX_CMRS, NULL, &out);
> +	if (ret)
> +		return ret;
> +
> +	/*
> +	 * If TDH.SYS.CONFIG succeeds, RDX contains the actual bytes
> +	 * written to @tdx_sysinfo and R9 contains the actual entries
> +	 * written to @tdx_cmr_array.  Sanity check them.
> +	 */
> +	tdsysinfo_sz = out.rdx;
> +	cmr_num = out.r9;

Please vertically align things like this:

	tdsysinfo_sz = out.rdx;
	cmr_num	     = out.r9;

> +	if (WARN_ON_ONCE((tdsysinfo_sz > sizeof(tdx_sysinfo)) || !tdsysinfo_sz ||
> +				(cmr_num > MAX_CMRS) || !cmr_num))
> +		return -EFAULT;

Sanity checking is good, but this makes me wonder how much is too much.
 I don't see a lot of code for instance checking if sys_write() writes
more than how much it was supposed to.

Why are these sanity checks necessary here?  Is the TDX module expected
to be *THAT* buggy?  The thing that's providing, oh, basically all of
the security guarantees of this architecture.  It's overflowing the
buffers you hand it?

> +	pr_info("TDX module: vendor_id 0x%x, major_version %u, minor_version %u, build_date %u, build_num %u",
> +		tdx_sysinfo.vendor_id, tdx_sysinfo.major_version,
> +		tdx_sysinfo.minor_version, tdx_sysinfo.build_date,
> +		tdx_sysinfo.build_num);
> +
> +	/* Print BIOS provided CMRs */
> +	print_cmrs(tdx_cmr_array, cmr_num, "BIOS-CMR");
> +
> +	return sanitize_cmrs(tdx_cmr_array, cmr_num);
> +}

Does sanitize_cmrs() sanitize anything?  It looks to me like it *checks*
the CMRs.  But, sanitizing is an active operation that writes to the
data being sanitized.  This looks read-only to me.  check_cmrs() would
be a better name for a passive check.

>  static int init_tdx_module(void)
>  {
>  	int ret;
> @@ -482,6 +608,11 @@ static int init_tdx_module(void)
>  	if (ret)
>  		goto out;
>  
> +	/* Get TDX module information and CMRs */
> +	ret = tdx_get_sysinfo();
> +	if (ret)
> +		goto out;

Couldn't we get rid of that comment if you did something like:

	ret = tdx_get_sysinfo(&tdx_cmr_array, &tdx_sysinfo);

and preferably make the variables function-local.

>  	/*
>  	 * Return -EFAULT until all steps of TDX module
>  	 * initialization are done.
> diff --git a/arch/x86/virt/vmx/tdx/tdx.h b/arch/x86/virt/vmx/tdx/tdx.h
> index b8cfdd6e12f3..2f21c45df6ac 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.h
> +++ b/arch/x86/virt/vmx/tdx/tdx.h
> @@ -29,6 +29,66 @@ struct p_seamldr_info {
>  	u8	reserved2[88];
>  } __packed __aligned(P_SEAMLDR_INFO_ALIGNMENT);
>  
> +struct cmr_info {
> +	u64	base;
> +	u64	size;
> +} __packed;
> +
> +#define MAX_CMRS			32
> +#define CMR_INFO_ARRAY_ALIGNMENT	512
> +
> +struct cpuid_config {
> +	u32	leaf;
> +	u32	sub_leaf;
> +	u32	eax;
> +	u32	ebx;
> +	u32	ecx;
> +	u32	edx;
> +} __packed;
> +
> +#define TDSYSINFO_STRUCT_SIZE		1024
> +#define TDSYSINFO_STRUCT_ALIGNMENT	1024
> +
> +struct tdsysinfo_struct {
> +	/* TDX-SEAM Module Info */
> +	u32	attributes;
> +	u32	vendor_id;
> +	u32	build_date;
> +	u16	build_num;
> +	u16	minor_version;
> +	u16	major_version;
> +	u8	reserved0[14];
> +	/* Memory Info */
> +	u16	max_tdmrs;
> +	u16	max_reserved_per_tdmr;
> +	u16	pamt_entry_size;
> +	u8	reserved1[10];
> +	/* Control Struct Info */
> +	u16	tdcs_base_size;
> +	u8	reserved2[2];
> +	u16	tdvps_base_size;
> +	u8	tdvps_xfam_dependent_size;
> +	u8	reserved3[9];
> +	/* TD Capabilities */
> +	u64	attributes_fixed0;
> +	u64	attributes_fixed1;
> +	u64	xfam_fixed0;
> +	u64	xfam_fixed1;
> +	u8	reserved4[32];
> +	u32	num_cpuid_config;
> +	/*
> +	 * The actual number of CPUID_CONFIG depends on above
> +	 * 'num_cpuid_config'.  The size of 'struct tdsysinfo_struct'
> +	 * is 1024B defined by TDX architecture.  Use a union with
> +	 * specific padding to make 'sizeof(struct tdsysinfo_struct)'
> +	 * equal to 1024.
> +	 */
> +	union {
> +		struct cpuid_config	cpuid_configs[0];
> +		u8			reserved5[892];
> +	};
> +} __packed __aligned(TDSYSINFO_STRUCT_ALIGNMENT);
> +
>  /*
>   * P-SEAMLDR SEAMCALL leaf function
>   */
> @@ -38,6 +98,7 @@ struct p_seamldr_info {
>  /*
>   * TDX module SEAMCALL leaf functions
>   */
> +#define TDH_SYS_INFO		32
>  #define TDH_SYS_INIT		33
>  #define TDH_SYS_LP_INIT		35
>  #define TDH_SYS_LP_SHUTDOWN	44