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cbfs: Allow mcache to be found after the first lookup 

This patch addresses the same problem as CB:48429, but hopefully this
time correctly. Since the mcache is not guaranteed to be available on
the first CBFS lookup for some special cases, we can no longer treat it
as a one-time fire-and-forget initialization. Instead, we test
cbd->mcache_size to check if the mcache has been initialized yet, and
keep trying on every lookup if we don't find it the first time.

Since the mcache is a hard requirement for TOCTOU safety, also make it
more clear in Kconfig that configurations known to do CBFS accesses
before CBMEM init are incompatbile with that, and make sure we die()
rather than do something unsafe if there's a case that Kconfig didn't
catch.

Signed-off-by: Julius Werner <jwerner@chromium.org>
Change-Id: I4e01e9a9905f7dcba14eaf05168495201ed5de60
Reviewed-on: https://review.coreboot.org/c/coreboot/+/48482
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Christian Walter <christian.walter@9elements.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
This commit is contained in:
Julius Werner 2020-12-08 14:21:43 -08:00
parent d2777b8485
commit 34cf073220
2 changed files with 12 additions and 3 deletions
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1
src/lib/Kconfig.cbfs_verification
View File

@ -19,6 +19,7 @@ config TOCTOU_SAFETY
depends on CBFS_VERIFICATION
depends on !NO_FMAP_CACHE
depends on !NO_CBFS_MCACHE
depends on !USE_OPTION_TABLE && !FSP_CAR # Known to access CBFS before CBMEM init
help
Work in progress. Not actually TOCTOU safe yet. Do not use.

14
src/lib/cbfs.c
View File

@ -27,7 +27,7 @@ cb_err_t cbfs_boot_lookup(const char *name, bool force_ro,
size_t data_offset;
cb_err_t err = CB_CBFS_CACHE_FULL;
if (!CONFIG(NO_CBFS_MCACHE) && !ENV_SMM)
if (!CONFIG(NO_CBFS_MCACHE) && !ENV_SMM && cbd->mcache_size)
err = cbfs_mcache_lookup(cbd->mcache, cbd->mcache_size,
name, mdata, &data_offset);
if (err == CB_CBFS_CACHE_FULL) {
@ -35,6 +35,8 @@ cb_err_t cbfs_boot_lookup(const char *name, bool force_ro,
if (CONFIG(TOCTOU_SAFETY)) {
if (ENV_SMM) /* Cannot provide TOCTOU safety for SMM */
dead_code();
if (!cbd->mcache_size)
die("Cannot access CBFS TOCTOU-safely in " ENV_STRING " before CBMEM init!\n");
/* We can only reach this for the RW CBFS -- an mcache
overflow in the RO CBFS would have been caught when
building the mcache in cbfs_get_boot_device().
@ -408,6 +410,9 @@ void cbfs_boot_device_find_mcache(struct cbfs_boot_device *cbd, uint32_t id)
if (CONFIG(NO_CBFS_MCACHE) || ENV_SMM)
return;
if (cbd->mcache_size)
return;
const struct cbmem_entry *entry;
if (cbmem_possibly_online() &&
(entry = cbmem_entry_find(id))) {
@ -465,14 +470,17 @@ const struct cbfs_boot_device *cbfs_get_boot_device(bool force_ro)
return rw;
}
/* In rare cases post-RAM stages may run this before cbmem_initialize(),
so we can't lock in the result of find_mcache() on the first try and
should keep trying every time until an mcache is found. */
cbfs_boot_device_find_mcache(&ro, CBMEM_ID_CBFS_RO_MCACHE);
if (region_device_sz(&ro.rdev))
return &ro;
if (fmap_locate_area_as_rdev("COREBOOT", &ro.rdev))
die("Cannot locate primary CBFS");
cbfs_boot_device_find_mcache(&ro, CBMEM_ID_CBFS_RO_MCACHE);
if (ENV_INITIAL_STAGE) {
cb_err_t err = cbfs_init_boot_device(&ro, metadata_hash_get());
if (err == CB_CBFS_HASH_MISMATCH)