cr50: Make sure TPM wipe only clears TPM data.

Previously, wiping the TPM would wipe all of NvMem, however, it really
should only clear the TPM's NvMem space.  This commit adds a function to
clear a given NvMem user's space and makes the TPM only clear its space.

BUG=chrome-os-partner:61597
BRANCH=None
TEST=Add code for using nvmem vars, create a test variable, add a user
to snappy, unlock the console, verify that the user is no longer present
on the system and the test nvmem var still exists.
TEST=make -j buildall

Change-Id: Ic98baa5166a1ef9ae76e910b1b9ab100300e947f
Signed-off-by: Aseda Aboagye <aaboagye@google.com>
Reviewed-on: https://chromium-review.googlesource.com/445803
Commit-Ready: Aseda Aboagye <aaboagye@chromium.org>
Tested-by: Aseda Aboagye <aaboagye@chromium.org>
Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>

2 files changed, 19 insertions, 12 deletions

diff --git a/common/nvmem.c b/common/nvmem.c
index 7ffde9d977..cb4abc3287 100644
--- a/common/nvmem.c
+++ b/common/nvmem.c
@@ -358,34 +358,41 @@ static int nvmem_get_partition_off(int user, uint32_t offset,
 	return EC_SUCCESS;
 }
 
-int nvmem_setup(void)
+int nvmem_erase_user_data(enum nvmem_users user)
 {
 	int part;
 	int ret;
+	uint32_t user_offset, user_size;
 
-	CPRINTS("Configuring NVMEM Flash Partition");
+	if (user >= NVMEM_NUM_USERS)
+		return EC_ERROR_INVAL;
 
-	part = nvmem_act_partition;
-	nvmem_act_partition = 0;
+	CPRINTS("Erasing NVMEM Flash Partition user: %d", user);
 
 	ret = EC_SUCCESS;
 
+	/* Find offset within cache. */
+	user_offset = nvmem_user_start_offset[user];
+	user_size = nvmem_user_sizes[user];
+
 	for (part = 0; part < NVMEM_NUM_PARTITIONS; part++) {
 		int rv;
 
-		memset(nvmem_cache, 0xff, NVMEM_PARTITION_SIZE);
+		/* Lock the cache buffer. */
+		nvmem_lock_cache();
+		/* Erase the user's data. */
+		memset(nvmem_cache + user_offset, 0xFF, user_size);
+
 		/*
 		 * Make sure the contents change between runs of
-		 * nvmem_save() so that both flash partitions are
+		 * nvmem_save() so that all flash partitions are
 		 * written with empty contents and different
 		 * generation numbers.
 		 */
 		((struct nvmem_partition *)nvmem_cache)->tag.generation = part;
-		/* Lock the cache buffer (unlocked by nvmem_save() */
-		nvmem_lock_cache();
-		rv = nvmem_save();
 
-		/* Even if one partition saving failed, let's keep going. */
+		/* Make a best effort to clear each partition. */
+		rv = nvmem_save();
 		if (rv != EC_SUCCESS)
 			ret = rv;
 	}
diff --git a/common/tpm_registers.c b/common/tpm_registers.c
index c2728522ae..cac79c725d 100644
--- a/common/tpm_registers.c
+++ b/common/tpm_registers.c
@@ -727,8 +727,8 @@ static void tpm_reset_now(int wipe_first)
 		cprints(CC_TASK, "%s: force EC off", __func__);
 		assert_ec_rst();
 
-		/* Now wipe nvmem */
-		wipe_result = nvmem_setup();
+		/* Now wipe the TPM's nvmem */
+		wipe_result = nvmem_erase_user_data(NVMEM_TPM);
 	} else {
 		wipe_result = EC_SUCCESS;
 	}