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Subject[PATCH v2] drm/nouveau/secboot: remove VLA usage
In preparation to enabling -Wvla, remove VLA. In this particular
case directly use macro NVKM_MSGQUEUE_CMDLINE_SIZE instead of local
variable cmdline_size. Also, remove cmdline_size as it is not
actually useful anymore.

The use of stack Variable Length Arrays needs to be avoided, as they
can be a vector for stack exhaustion, which can be both a runtime bug
or a security flaw. Also, in general, as code evolves it is easy to
lose track of how big a VLA can get. Thus, we can end up having runtime
failures that are hard to debug.

Also, fixed as part of the directive to remove all VLAs from
the kernel: https://lkml.org/lkml/2018/3/7/621

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
Changes in v2:
- Use sizeof(buf) instead of NVKM_MSGQUEUE_CMDLINE_SIZE. This change
is based on the feedback provided by David Laight. Thanks David.

drivers/gpu/drm/nouveau/nvkm/subdev/secboot/ls_ucode_msgqueue.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/secboot/ls_ucode_msgqueue.c b/drivers/gpu/drm/nouveau/nvkm/subdev/secboot/ls_ucode_msgqueue.c
index 6f10b09..1e1f1c6 100644
--- a/drivers/gpu/drm/nouveau/nvkm/subdev/secboot/ls_ucode_msgqueue.c
+++ b/drivers/gpu/drm/nouveau/nvkm/subdev/secboot/ls_ucode_msgqueue.c
@@ -80,12 +80,11 @@ acr_ls_msgqueue_post_run(struct nvkm_msgqueue *queue,
struct nvkm_falcon *falcon, u32 addr_args)
{
struct nvkm_device *device = falcon->owner->device;
- u32 cmdline_size = NVKM_MSGQUEUE_CMDLINE_SIZE;
- u8 buf[cmdline_size];
+ u8 buf[NVKM_MSGQUEUE_CMDLINE_SIZE];

- memset(buf, 0, cmdline_size);
+ memset(buf, 0, sizeof(buf));
nvkm_msgqueue_write_cmdline(queue, buf);
- nvkm_falcon_load_dmem(falcon, buf, addr_args, cmdline_size, 0);
+ nvkm_falcon_load_dmem(falcon, buf, addr_args, sizeof(buf), 0);
/* rearm the queue so it will wait for the init message */
nvkm_msgqueue_reinit(queue);

--
2.7.4
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