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From: "Gustavo A. R. Silva" <>
To: David Laight <David.Laight@ACULAB.COM>,
	Ben Skeggs <>, David Airlie <>
	"Gustavo A. R. Silva" <>
Subject: [PATCH v2] drm/nouveau/secboot: remove VLA usage
Date: Tue, 13 Mar 2018 11:24:11 -0500	[thread overview]
Message-ID: <20180313162411.GA1983@embeddedgus> (raw)

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:

Signed-off-by: Gustavo A. R. Silva <>
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];
-	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 */

             reply	other threads:[~2018-03-13 16:24 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-13 16:24 Gustavo A. R. Silva [this message]
2018-03-14 11:08 ` Thierry Reding
2018-03-16  2:05   ` Ben Skeggs
2018-04-26 23:25     ` Kees Cook
2018-05-23 22:48       ` Kees Cook
2018-05-24  0:36         ` Ben Skeggs
2018-05-24  0:47           ` Kees Cook

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