[RFC PATCH 6/6] ima: prevent loading firmware into a pre-allocated buffer

[Mimi Zohar <zohar@linux.vnet.ibm.com>]

Question: can the device access the pre-allocated buffer at any time?

By allowing devices to request firmware be loaded directly into a
pre-allocated buffer, will this allow the device access to the firmware
before the kernel has verified the firmware signature?

Is it dependent on the type of buffer allocated (eg. DMA)?  For example,
qcom_mdt_load() -> qcom_scm_pas_init_image() -> dma_alloc_coherent().

With an IMA policy requiring signed firmware, this patch would prevent
loading firmware into a pre-allocated buffer.

Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Cc: Luis R. Rodriguez <mcgrof@suse.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Serge E. Hallyn <serge@hallyn.com>
Cc: Stephen Boyd <stephen.boyd@linaro.org>
---
 security/integrity/ima/ima_main.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index eb9c273ab81d..3098131f77c4 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -454,6 +454,15 @@ int ima_read_file(struct file *file, enum kernel_read_file_id read_id)
 		return 0;
 	}
 
+	if (read_id == READING_FIRMWARE_PREALLOC_BUFFER) {
+		if ((ima_appraise & IMA_APPRAISE_FIRMWARE) &&
+		    (ima_appraise & IMA_APPRAISE_ENFORCE)) {
+			pr_err("Prevent device from accessing firmware prior to verifying the firmware signature.\n");
+			return -EACCES;
+		}
+		return 0;
+	}
+
 	if (read_id == READING_FIRMWARE_FALLBACK) {
 		if ((ima_appraise & IMA_APPRAISE_FIRMWARE) &&
 		    (ima_appraise & IMA_APPRAISE_ENFORCE)) {
-- 
2.7.5