[PATCH 70/82] remoteproc: Refactor intentional wrap-around test

[Kees Cook]

In an effort to separate intentional arithmetic wrap-around from
unexpected wrap-around, we need to refactor places that depend on this
kind of math. One of the most common code patterns of this is:

	VAR + value < VAR

Notably, this is considered "undefined behavior" for signed and pointer
types, which the kernel works around by using the -fno-strict-overflow
option in the build[1] (which used to just be -fwrapv). Regardless, we
want to get the kernel source to the position where we can meaningfully
instrument arithmetic wrap-around conditions and catch them when they
are unexpected, regardless of whether they are signed[2], unsigned[3],
or pointer[4] types.

Refactor open-coded wrap-around addition test to use add_would_overflow().
This paves the way to enabling the wrap-around sanitizers in the future.

Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1]
Link: https://github.com/KSPP/linux/issues/26 [2]
Link: https://github.com/KSPP/linux/issues/27 [3]
Link: https://github.com/KSPP/linux/issues/344 [4]
Cc: Bjorn Andersson <andersson@xxxxxxxxxx>
Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
Cc: linux-remoteproc@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 drivers/remoteproc/pru_rproc.c             | 2 +-
 drivers/remoteproc/remoteproc_elf_loader.c | 2 +-
 drivers/remoteproc/remoteproc_virtio.c     | 4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/remoteproc/pru_rproc.c b/drivers/remoteproc/pru_rproc.c
index 327f0c7ee3d6..834249ee3dd3 100644
--- a/drivers/remoteproc/pru_rproc.c
+++ b/drivers/remoteproc/pru_rproc.c
@@ -893,7 +893,7 @@ pru_rproc_find_interrupt_map(struct device *dev, const struct firmware *fw)
 			continue;
 
 		/* make sure we have the entire irq map */
-		if (offset + size > fw->size || offset + size < size) {
+		if (offset + size > fw->size || add_would_overflow(size, offset)) {
 			dev_err(dev, ".pru_irq_map section truncated\n");
 			return ERR_PTR(-EINVAL);
 		}
diff --git a/drivers/remoteproc/remoteproc_elf_loader.c b/drivers/remoteproc/remoteproc_elf_loader.c
index 94177e416047..b9231cf46d68 100644
--- a/drivers/remoteproc/remoteproc_elf_loader.c
+++ b/drivers/remoteproc/remoteproc_elf_loader.c
@@ -278,7 +278,7 @@ find_table(struct device *dev, const struct firmware *fw)
 		table = (struct resource_table *)(elf_data + offset);
 
 		/* make sure we have the entire table */
-		if (offset + size > fw_size || offset + size < size) {
+		if (offset + size > fw_size || add_would_overflow(size, offset)) {
 			dev_err(dev, "resource table truncated\n");
 			return NULL;
 		}
diff --git a/drivers/remoteproc/remoteproc_virtio.c b/drivers/remoteproc/remoteproc_virtio.c
index 83d76915a6ad..58742c666e35 100644
--- a/drivers/remoteproc/remoteproc_virtio.c
+++ b/drivers/remoteproc/remoteproc_virtio.c
@@ -298,7 +298,7 @@ static void rproc_virtio_get(struct virtio_device *vdev, unsigned int offset,
 	rsc = (void *)rvdev->rproc->table_ptr + rvdev->rsc_offset;
 	cfg = &rsc->vring[rsc->num_of_vrings];
 
-	if (offset + len > rsc->config_len || offset + len < len) {
+	if (offset + len > rsc->config_len || add_would_overflow(len, offset)) {
 		dev_err(&vdev->dev, "rproc_virtio_get: access out of bounds\n");
 		return;
 	}
@@ -316,7 +316,7 @@ static void rproc_virtio_set(struct virtio_device *vdev, unsigned int offset,
 	rsc = (void *)rvdev->rproc->table_ptr + rvdev->rsc_offset;
 	cfg = &rsc->vring[rsc->num_of_vrings];
 
-	if (offset + len > rsc->config_len || offset + len < len) {
+	if (offset + len > rsc->config_len || add_would_overflow(len, offset)) {
 		dev_err(&vdev->dev, "rproc_virtio_set: access out of bounds\n");
 		return;
 	}
-- 
2.34.1