coreboot-kgpe-d16/util/cbfstool/platform_fixups.c

122 lines
4.3 KiB
C
Raw Normal View History

cbfstool: Add support for platform "fixups" when modifying bootblock To support the new CONFIG_CBFS_VERIFICATION feature, cbfstool needs to update the metadata hash embedded in the bootblock code every time it adds or removes a CBFS file. This can lead to problems on certain platforms where the bootblock needs to be specially wrapped in some platform-specific data structure so that the platform's masked ROM can recognize it. If that data structure contains any form of hash or signature of the bootblock code that is checked on every boot, it will no longer match if cbfstool modifies it after the fact. In general, we should always try to disable these kinds of features where possible (they're not super useful anyway). But for platforms where the hardware simply doesn't allow that, this patch introduces the concept of "platform fixups" to cbfstool. Whenever cbfstool finds a metadata hash anchor in a CBFS image, it will run all built-in "fixup probe" functions on that bootblock to check if it can recognize it as the wrapper format for a platform known to have such an issue. If so, it will register a corresponding fixup function that will run whenever it tries to write back modified data to that bootblock. The function can then modify any platform-specific headers as necessary. As first supported platform, this patch adds a fixup for Qualcomm platforms (specifically the header format used by sc7180), which recalculates the bootblock body hash originally added by util/qualcomm/createxbl.py. (Note that this feature is not intended to support platform-specific signature schemes like BootGuard directly in cbfstool. For anything that requires an actual secret key, it should be okay if the user needs to run a platform-specific signing tool on the final CBFS image before flashing. This feature is intended for the normal unsigned case (which on some platforms may be implemented as signing with a well-known key) so that on a board that is not "locked down" in any way the normal use case of manipulating an image with cbfstool and then directly flashing the output file stays working with CONFIG_CBFS_VERIFICATION.) Signed-off-by: Julius Werner <jwerner@chromium.org> Change-Id: I02a83a40f1d0009e6f9561ae5d2d9f37a510549a Reviewed-on: https://review.coreboot.org/c/coreboot/+/41122 Reviewed-by: Angel Pons <th3fanbus@gmail.com> Reviewed-by: Aaron Durbin <adurbin@chromium.org> Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
2020-03-20 05:09:35 +01:00
/* SPDX-License-Identifier: GPL-2.0-only */
#include "cbfs.h"
#include "cbfs_sections.h"
#include "elfparsing.h"
/*
* NOTE: This currently only implements support for MBN version 6 (as used by sc7180). Support
* for other MBN versions could probably be added but may require more parsing to tell them
* apart, and minor modifications (e.g. different hash algorithm). Add later as needed.
*/
static void *qualcomm_find_hash(struct buffer *in, size_t bb_offset, struct vb2_hash *real_hash)
{
struct buffer elf;
buffer_clone(&elf, in);
/* When buffer_size(&elf) becomes this small, we know we've searched through 32KiB (or
the whole bootblock) without finding anything, so we know we can stop looking. */
size_t search_end_size = MIN(0, buffer_size(in) - 32 * KiB);
/* To identify a Qualcomm image, first we find the GPT header... */
while (buffer_size(&elf) > search_end_size &&
!buffer_check_magic(&elf, "EFI PART", 8))
buffer_seek(&elf, 512);
/* ...then shortly afterwards there's an ELF header... */
while (buffer_size(&elf) > search_end_size &&
!buffer_check_magic(&elf, ELFMAG, 4))
buffer_seek(&elf, 512);
if (buffer_size(&elf) <= search_end_size)
return NULL; /* Doesn't seem to be a Qualcomm image. */
struct parsed_elf pelf;
if (parse_elf(&elf, &pelf, ELF_PARSE_PHDR))
return NULL; /* Not an ELF -- guess not a Qualcomm MBN after all? */
/* Qualcomm stores an array of SHA-384 hashes in a special ELF segment. One special one
to start with, and then one for each segment in order. */
void *bb_hash = NULL;
void *hashtable = NULL;
int i;
int bb_segment = -1;
for (i = 0; i < pelf.ehdr.e_phnum; i++) {
Elf64_Phdr *ph = &pelf.phdr[i];
if ((ph->p_flags & PF_QC_SG_MASK) == PF_QC_SG_HASH) {
if ((int)ph->p_filesz !=
(pelf.ehdr.e_phnum + 1) * VB2_SHA384_DIGEST_SIZE) {
ERROR("fixups: Qualcomm hash segment has wrong size!\n");
goto destroy_elf;
} /* Found the table with the hashes -- store its address. */
hashtable = buffer_get(&elf) + ph->p_offset;
} else if (bb_segment < 0 && ph->p_offset + ph->p_filesz < buffer_size(&elf) &&
buffer_offset(&elf) + ph->p_offset <= bb_offset &&
buffer_offset(&elf) + ph->p_offset + ph->p_filesz > bb_offset) {
bb_segment = i; /* Found the bootblock segment -- store its index. */
}
}
if (!hashtable) /* ELF but no special QC hash segment -- guess not QC after all? */
goto destroy_elf;
if (bb_segment < 0) { /* Can assume it's QC if we found the special segment. */
ERROR("fixups: Cannot find bootblock code in Qualcomm MBN!\n");
goto destroy_elf;
}
/* Pass out the actual hash of the current bootblock segment in |real_hash|. */
if (vb2_hash_calculate(buffer_get(&elf) + pelf.phdr[bb_segment].p_offset,
pelf.phdr[bb_segment].p_filesz, VB2_HASH_SHA384, real_hash)) {
ERROR("fixups: vboot digest error\n");
goto destroy_elf;
} /* Return pointer to where the bootblock hash needs to go in Qualcomm's table. */
bb_hash = hashtable + (bb_segment + 1) * VB2_SHA384_DIGEST_SIZE;
destroy_elf:
parsed_elf_destroy(&pelf);
return bb_hash;
}
static bool qualcomm_probe(struct buffer *buffer, size_t offset)
{
struct vb2_hash real_hash;
void *table_hash = qualcomm_find_hash(buffer, offset, &real_hash);
if (!table_hash)
return false;
if (memcmp(real_hash.raw, table_hash, VB2_SHA384_DIGEST_SIZE)) {
ERROR("fixups: Identified Qualcomm MBN, but existing hash doesn't match!\n");
return false;
}
return true;
}
static int qualcomm_fixup(struct buffer *buffer, size_t offset)
{
struct vb2_hash real_hash;
void *table_hash = qualcomm_find_hash(buffer, offset, &real_hash);
if (!table_hash) {
ERROR("fixups: Cannot find Qualcomm MBN headers anymore!\n");
return -1;
}
memcpy(table_hash, real_hash.raw, VB2_SHA384_DIGEST_SIZE);
INFO("fixups: Updated Qualcomm MBN header bootblock hash.\n");
return 0;
}
platform_fixup_func platform_fixups_probe(struct buffer *buffer, size_t offset,
const char *region_name)
{
if (!strcmp(region_name, SECTION_NAME_BOOTBLOCK)) {
if (qualcomm_probe(buffer, offset))
return qualcomm_fixup;
} else if (!strcmp(region_name, SECTION_NAME_PRIMARY_CBFS)) {
/* TODO: add fixups for primary CBFS bootblock platforms, if needed */
} else {
ERROR("%s called for unexpected FMAP region %s!\n", __func__, region_name);
}
return NULL;
}