From 4f0496d8ffa3ed5956a2ddee5d84f0246977799d Mon Sep 17 00:00:00 2001 From: Mimi Zohar Date: Fri, 13 Jul 2018 14:06:03 -0400 Subject: [PATCH] ima: based on policy warn about loading firmware (pre-allocated buffer) Some systems are memory constrained but they need to load very large firmwares. The firmware subsystem allows drivers to request this firmware be loaded from the filesystem, but this requires that the entire firmware be loaded into kernel memory first before it's provided to the driver. This can lead to a situation where we map the firmware twice, once to load the firmware into kernel memory and once to copy the firmware into the final resting place. To resolve this problem, commit a098ecd2fa7d ("firmware: support loading into a pre-allocated buffer") introduced request_firmware_into_buf() API that allows drivers to request firmware be loaded directly into a pre-allocated buffer. Do devices using pre-allocated memory run the risk of the firmware being accessible to the device prior to the completion of IMA's signature verification any more than when using two buffers? (Refer to mailing list discussion[1]). Only on systems with an IOMMU can the access be prevented. As long as the signature verification completes prior to the DMA map is performed, the device can not access the buffer. This implies that the same buffer can not be re-used. Can we ensure the buffer has not been DMA mapped before using the pre-allocated buffer? [1] https://lkml.org/lkml/2018/7/10/56 Signed-off-by: Mimi Zohar Cc: Luis R. Rodriguez Cc: Stephen Boyd Cc: Bjorn Andersson Cc: Ard Biesheuvel Reviewed-by: Kees Cook Signed-off-by: James Morris --- security/integrity/ima/ima_main.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c index ef349a761609..dce0a8a217bb 100644 --- a/security/integrity/ima/ima_main.c +++ b/security/integrity/ima/ima_main.c @@ -429,6 +429,14 @@ void ima_post_path_mknod(struct dentry *dentry) */ int ima_read_file(struct file *file, enum kernel_read_file_id read_id) { + /* + * READING_FIRMWARE_PREALLOC_BUFFER + * + * Do devices using pre-allocated memory run the risk of the + * firmware being accessible to the device prior to the completion + * of IMA's signature verification any more than when using two + * buffers? + */ return 0; }