[coreboot-gerrit] Change in coreboot[master]: cbfs: Allow mcache to be found after the first lookup

[Julius Werner (Code Review)]

Julius Werner has submitted this change. ( https://review.coreboot.org/c/coreboot/+/48482 )

Change subject: cbfs: Allow mcache to be found after the first lookup
......................................................................

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 
Change-Id: I4e01e9a9905f7dcba14eaf05168495201ed5de60
Reviewed-on: https://review.coreboot.org/c/coreboot/+/48482
Tested-by: build bot (Jenkins) 
Reviewed-by: Arthur Heymans 
Reviewed-by: Christian Walter 
Reviewed-by: Angel Pons 
---
M src/lib/Kconfig.cbfs_verification
M src/lib/cbfs.c
2 files changed, 12 insertions(+), 3 deletions(-)

Approvals:
  build bot (Jenkins): Verified
  Arthur Heymans: Looks good to me, approved
  Angel Pons: Looks good to me, but someone else must approve
  Christian Walter: Looks good to me, approved

diff --git a/src/lib/Kconfig.cbfs_verification b/src/lib/Kconfig.cbfs_verification
index 3499345..4e2ed8c 100644
--- a/src/lib/Kconfig.cbfs_verification
+++ b/src/lib/Kconfig.cbfs_verification
@@ -19,6 +19,7 @@
    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.

diff --git a/src/lib/cbfs.c b/src/lib/cbfs.c
index d275505..60dc15a 100644
--- a/src/lib/cbfs.c
+++ b/src/lib/cbfs.c
@@ -27,7 +27,7 @@

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 @@
    	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 @@
    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 @@
    		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)