Re: [GRUB PATCH RFC 15/18] i386/txt: Add Intel TXT core implementation

[Krystian Hebel]

On 05.05.2020 01:21, Daniel Kiper wrote:
> +static grub_err_t
> +init_txt_heap (struct grub_slaunch_params *slparams, struct grub_txt_acm_header *sinit)
> +{
> +  grub_uint8_t *txt_heap;
> +  grub_uint32_t os_sinit_data_ver, sinit_caps;
> +  grub_uint64_t *size;
> +  struct grub_txt_os_mle_data *os_mle_data;
> +  struct grub_txt_os_sinit_data *os_sinit_data;
> +  struct grub_txt_heap_end_element *heap_end_element;
> +  struct grub_txt_heap_event_log_pointer2_1_element *heap_event_log_pointer2_1_element;
> +#ifdef GRUB_MACHINE_EFI
> +  struct grub_acpi_rsdp_v20 *rsdp;
> +#endif
> +
> +  /* BIOS data already verified in grub_txt_verify_platform(). */
> +
> +  txt_heap = grub_txt_get_heap ();
> +
> +  /* OS/loader to MLE data. */
> +
> +  os_mle_data = grub_txt_os_mle_data_start (txt_heap);
> +  size = (grub_uint64_t *) ((grub_addr_t) os_mle_data - sizeof (grub_uint64_t));
There is 'grub_txt_os_mle_data_size()' in previous patch, it would look 
better.
> +  *size = sizeof (*os_mle_data) + sizeof (grub_uint64_t);
> +
> +  grub_memset (os_mle_data, 0, sizeof (*os_mle_data));
> +
> +  os_mle_data->version = GRUB_SL_OS_MLE_STRUCT_VERSION;
> +  os_mle_data->zero_page_addr = (grub_uint32_t)(grub_addr_t) slparams->params;
> +  os_mle_data->saved_misc_enable_msr = grub_rdmsr (GRUB_MSR_X86_MISC_ENABLE);
> +
> +  os_mle_data->ap_wake_block = slparams->ap_wake_block;
> +
> +  save_mtrrs (os_mle_data);
> +
> +  /* OS/loader to SINIT data. */
> +
> +  os_sinit_data_ver = grub_txt_supported_os_sinit_data_ver (sinit);
> +
> +  if (os_sinit_data_ver < OS_SINIT_DATA_MIN_VER)
> +    return grub_error (GRUB_ERR_BAD_DEVICE,
> +		       N_("unsupported OS to SINIT data version in SINIT ACM: %d"
> +		       " expected >= %d"), os_sinit_data_ver, OS_SINIT_DATA_MIN_VER);
> +
> +  os_sinit_data = grub_txt_os_sinit_data_start (txt_heap);
> +  size = (grub_uint64_t *) ((grub_addr_t) os_sinit_data - sizeof (grub_uint64_t));
Ditto
> +
> +  *size = sizeof(grub_uint64_t) + sizeof (struct grub_txt_os_sinit_data) +
> +	  sizeof (struct grub_txt_heap_end_element);
> +
> +  if (grub_get_tpm_ver () == GRUB_TPM_12)
> +    *size += sizeof (struct grub_txt_heap_tpm_event_log_element);
> +  else if (grub_get_tpm_ver () == GRUB_TPM_20)
> +    *size += sizeof (struct grub_txt_heap_event_log_pointer2_1_element);
> +  else
> +    return grub_error (GRUB_ERR_BAD_DEVICE, N_("unsupported TPM version"));
> +
> +  grub_memset (os_sinit_data, 0, *size);
> +
> +#ifdef GRUB_MACHINE_EFI
> +  rsdp = grub_acpi_get_rsdpv2 ();
> +
> +  if (rsdp == NULL)
> +    return grub_printf ("WARNING: ACPI RSDP 2.0 missing\n");
> +
> +  os_sinit_data->efi_rsdt_ptr = (grub_uint64_t)(grub_addr_t) rsdp;
> +#endif
> +
> +  os_sinit_data->mle_ptab = slparams->mle_ptab_target;
> +  os_sinit_data->mle_size = slparams->mle_size;
> +
> +  os_sinit_data->mle_hdr_base = slparams->mle_header_offset;
> +
> +  /* TODO: Check low PMR with RMRR. Look at relevant tboot code too. */
> +  /* TODO: Kernel should not allocate any memory outside of PMRs regions!!! */
> +  os_sinit_data->vtd_pmr_lo_base = 0;
> +  os_sinit_data->vtd_pmr_lo_size = ALIGN_DOWN (grub_mmap_get_highest (0x100000000),
> +					       GRUB_TXT_PMR_ALIGN);
> +
> +  os_sinit_data->vtd_pmr_hi_base = ALIGN_UP (grub_mmap_get_lowest (0x100000000),
> +					     GRUB_TXT_PMR_ALIGN);
> +  os_sinit_data->vtd_pmr_hi_size = ALIGN_DOWN (grub_mmap_get_highest (0xffffffffffffffff),
> +					       GRUB_TXT_PMR_ALIGN);
> +  os_sinit_data->vtd_pmr_hi_size -= os_sinit_data->vtd_pmr_hi_base;
Could it be done with just one PMR, from 0 to top of memory, or would 
TXT complain?
> +
> +  grub_dprintf ("slaunch",
> +		"vtd_pmr_lo_base: 0x%" PRIxGRUB_UINT64_T " vtd_pmr_lo_size: 0x%"
> +		PRIxGRUB_UINT64_T " vtd_pmr_hi_base: 0x%" PRIxGRUB_UINT64_T
> +		" vtd_pmr_hi_size: 0x%" PRIxGRUB_UINT64_T "\n",
> +		os_sinit_data->vtd_pmr_lo_base, os_sinit_data->vtd_pmr_lo_size,
> +		os_sinit_data->vtd_pmr_hi_base, os_sinit_data->vtd_pmr_hi_size);
> +
>
> <snip>
>
> +/*
> + * The MLE page tables have to be below the MLE and have no special regions in
> + * between them and the MLE (this is a bit of an unwritten rule).
> + * 20 pages are carved out of memory below the MLE. That leave 18 page table
> + * pages that can cover up to 36M .
> + * can only contain 4k pages
> + *
> + * TODO: TXT Spec p.32; List section name and number with PT MLE requirments here.
> + *
> + * TODO: This function is not able to cover MLEs larger than 1 GiB. Fix it!!!
> + * After fixing inrease GRUB_TXT_MLE_MAX_SIZE too.
> + */

What do you mean by "special regions"? In TXT spec it is written that 
there may be no holes
in the virtual address space:

"There may not be any invalid (not-present) page table entries after the 
first valid
entry (i.e. there may not be any gaps in the MLEâs linear address space)."

Also that spec:
"A breadth-first search of page tables must produce increasing physical 
addresses."

Maybe I misunderstood, but does it mean that the paging structures 
themselves cannot
be mapped? Or does it apply to the page tables only, not to the 
addresses of pages in PTEs?

> +void
> +grub_txt_setup_mle_ptab (struct grub_slaunch_params *slparams)
> +{
> +  grub_uint8_t *pg_dir, *pg_dir_ptr_tab = slparams->mle_ptab_mem, *pg_tab;
IMHO using 'grub_uint64_t' would result in less type casting and cleaner 
code below.
> +  grub_uint32_t mle_off = 0, pd_off = 0;
> +  grub_uint64_t *pde, *pte;
> +
> +  grub_memset (pg_dir_ptr_tab, 0, slparams->mle_ptab_size);
> +
> +  pg_dir         = pg_dir_ptr_tab + GRUB_PAGE_SIZE;
> +  pg_tab         = pg_dir + GRUB_PAGE_SIZE;
> +
> +  /* Only use first entry in page dir ptr table */
> +  *(grub_uint64_t *)pg_dir_ptr_tab = MAKE_PT_MLE_ENTRY(pg_dir);
> +
> +  /* Start with first entry in page dir */
> +  *(grub_uint64_t *)pg_dir = MAKE_PT_MLE_ENTRY(pg_tab);
> +
> +  pte = (grub_uint64_t *)pg_tab;
> +  pde = (grub_uint64_t *)pg_dir;
> +
> +  do
> +    {
> +      *pte = MAKE_PT_MLE_ENTRY(slparams->mle_start + mle_off);
> +
> +      pte++;
> +      mle_off += GRUB_PAGE_SIZE;
> +
> +      if (!(++pd_off % 512))
> +        {
> +          /* Break if we don't need any additional page entries */
> +          if (mle_off >= slparams->mle_size)
> +            break;
> +          pde++;
> +          *pde = MAKE_PT_MLE_ENTRY(pte);
> +        }
> +    } while (mle_off < slparams->mle_size);
> +}
>
> <snip>
>
> +grub_err_t
> +grub_txt_boot_prepare (struct grub_slaunch_params *slparams)
> +{
> +  grub_err_t err;
> +  struct grub_txt_mle_header *mle_header;
> +  struct grub_txt_acm_header *sinit_base;
> +
> +  sinit_base = grub_txt_sinit_select (grub_slaunch_module ());
> +
> +  if (sinit_base == NULL)
> +    return grub_errno;
> +
> +  err = init_txt_heap (slparams, sinit_base);
> +
> +  if (err != GRUB_ERR_NONE)
> +    return err;
> +
> +  /* Update the MLE header. */
> +  mle_header = (struct grub_txt_mle_header *)(grub_addr_t) (slparams->mle_start + slparams->mle_header_offset);
> +  mle_header->first_valid_page = 0;
> +  mle_header->mle_end = slparams->mle_size;
> +
> +  slparams->sinit_acm_base = (grub_uint32_t)(grub_addr_t) sinit_base;
> +  slparams->sinit_acm_size = sinit_base->size * 4;
> +
> +  grub_tpm_relinquish_lcl (0);
> +
> +  err = set_mtrrs_for_acmod (sinit_base);
> +  if (err)
> +    return grub_error (err, N_("secure launch failed to set MTRRs for ACM"));
> +
> +  err = grub_txt_prepare_cpu ();
> +  if ( err )
> +    return err;
> +
> +  if (!(grub_rdmsr (GRUB_MSR_X86_APICBASE) & GRUB_MSR_X86_APICBASE_BSP))
> +    return grub_error (GRUB_ERR_BAD_DEVICE, N_("secure launch must run on BSP"));
This test should be the first one, before messing with TPM and MTTRs.
> +
> +  return GRUB_ERR_NONE;
> +}
Best regards,

--
Krystian Hebel
Firmware Engineer
https://3mdeb.com | @3mdeb_com