Re: [PATCH v2] drm/fbdev-generic: prohibit potential out-of-bounds access
From: Sui Jingfeng
Date: Fri Apr 28 2023 - 04:09:08 EST
Hi,
On 2023/4/27 17:34, Daniel Vetter wrote:
On Thu, Apr 20, 2023 at 02:47:24AM +0800, Sui Jingfeng wrote:
Hi,
On 2023/4/17 15:29, Thomas Zimmermann wrote:
Hi
Am 14.04.23 um 12:58 schrieb Sui Jingfeng:
Hi,
On 2023/4/14 03:16, Thomas Zimmermann wrote:
Hi,
thanks for the patch. This is effectively a revert of commit
8fbc9af55de0 ("drm/fbdev-generic: Set screen size to size of GEM
buffer"). Please add a Fixes tag.
Am 13.04.23 um 20:06 schrieb Sui Jingfeng:
From: Sui Jingfeng <suijingfeng@xxxxxxxxxxx>
The crazy fbdev test of IGT may write after EOF, which lead
to out-of-bound
Please drop 'crazy'. :)
This is OK.
By using the world 'crazy',
I meant that the test is very good and maybe it is written by
professional peoples
with the guidance by experienced engineer. So that even the corner
get tested.
access for the drm drivers using fbdev-generic. For example,
run fbdev test
on a x86-64+ast2400 platform with 1680x1050 resolution will
cause the linux
kernel hang with following call trace:
Oops: 0000 [#1] PREEMPT SMP PTI
[IGT] fbdev: starting subtest eof
Workqueue: events drm_fb_helper_damage_work [drm_kms_helper]
[IGT] fbdev: starting subtest nullptr
RIP: 0010:memcpy_erms+0xa/0x20
RSP: 0018:ffffa17d40167d98 EFLAGS: 00010246
RAX: ffffa17d4eb7fa80 RBX: ffffa17d40e0aa80 RCX: 00000000000014c0
RDX: 0000000000001a40 RSI: ffffa17d40e0b000 RDI: ffffa17d4eb80000
RBP: ffffa17d40167e20 R08: 0000000000000000 R09: ffff89522ecff8c0
R10: ffffa17d4e4c5000 R11: 0000000000000000 R12: ffffa17d4eb7fa80
R13: 0000000000001a40 R14: 000000000000041a R15: ffffa17d40167e30
FS: 0000000000000000(0000) GS:ffff895257380000(0000)
knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffa17d40e0b000 CR3: 00000001eaeca006 CR4: 00000000001706e0
Call Trace:
<TASK>
? drm_fbdev_generic_helper_fb_dirty+0x207/0x330 [drm_kms_helper]
drm_fb_helper_damage_work+0x8f/0x170 [drm_kms_helper]
process_one_work+0x21f/0x430
worker_thread+0x4e/0x3c0
? __pfx_worker_thread+0x10/0x10
kthread+0xf4/0x120
? __pfx_kthread+0x10/0x10
ret_from_fork+0x2c/0x50
</TASK>
CR2: ffffa17d40e0b000
---[ end trace 0000000000000000 ]---
The indirect reason is drm_fb_helper_memory_range_to_clip()
generate damage
rectangles which partially or completely go out of the
active display area.
The second of argument 'off' is passing from the user-space,
this will lead
to the out-of-bound if it is large than (fb_height + 1) *
fb_pitches; while
DIV_ROUND_UP() may also controbute to error by 1.
This patch will add code to restrict the damage rect
computed go beyond of
the last line of the framebuffer.
Signed-off-by: Sui Jingfeng <suijingfeng@xxxxxxxxxxx>
---
drivers/gpu/drm/drm_fb_helper.c | 16 ++++++++++++----
drivers/gpu/drm/drm_fbdev_generic.c | 2 +-
2 files changed, 13 insertions(+), 5 deletions(-)
diff --git a/drivers/gpu/drm/drm_fb_helper.c
b/drivers/gpu/drm/drm_fb_helper.c
index 64458982be40..6bb1b8b27d7a 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -641,19 +641,27 @@ static void
drm_fb_helper_damage(struct drm_fb_helper *helper, u32 x,
u32 y,
static void drm_fb_helper_memory_range_to_clip(struct
fb_info *info, off_t off, size_t len,
struct drm_rect *clip)
{
+ u32 line_length = info->fix.line_length;
+ u32 fb_height = info->var.yres;
off_t end = off + len;
u32 x1 = 0;
- u32 y1 = off / info->fix.line_length;
+ u32 y1 = off / line_length;
u32 x2 = info->var.xres;
- u32 y2 = DIV_ROUND_UP(end, info->fix.line_length);
+ u32 y2 = DIV_ROUND_UP(end, line_length);
+
+ /* Don't allow any of them beyond the bottom bound of
display area */
+ if (y1 > fb_height)
+ y1 = fb_height;
+ if (y2 > fb_height)
+ y2 = fb_height;
if ((y2 - y1) == 1) {
/*
* We've only written to a single scanline. Try to reduce
* the number of horizontal pixels that need an update.
*/
- off_t bit_off = (off % info->fix.line_length) * 8;
- off_t bit_end = (end % info->fix.line_length) * 8;
+ off_t bit_off = (off % line_length) * 8;
+ off_t bit_end = (end % line_length) * 8;
Please scratch all these changes. The current code should work
as intended. Only the generic fbdev emulation uses this code and
it should really be moved there at some point.
Are you meant that we should remove all these changes in
drivers/gpu/drm/drm_fb_helper.c ?
As Daniel mentioned, there's the discussion in the other thread. I don't
want to reopen it here. Just to summarize: I'm not convinced that this
should be DRM code because it can be shared with other fbdev drivers.
[...]
diff --git a/drivers/gpu/drm/drm_fbdev_generic.c
b/drivers/gpu/drm/drm_fbdev_generic.c
index 8e5148bf40bb..b057cfbba938 100644
--- a/drivers/gpu/drm/drm_fbdev_generic.c
+++ b/drivers/gpu/drm/drm_fbdev_generic.c
@@ -94,7 +94,7 @@ static int
drm_fbdev_generic_helper_fb_probe(struct drm_fb_helper
*fb_helper,
fb_helper->buffer = buffer;
fb_helper->fb = buffer->fb;
- screen_size = buffer->gem->size;
+ screen_size = sizes->surface_height * buffer->fb->pitches[0];
This has been bothering me over the weekend. And I think it's because
what we want the screen_size to be heigth * pitch, but the mmap'ed
memory is still at page granularity. Therefore...
[...]
screen_buffer = vzalloc(screen_size);
... this line should explicitly allocate multiples of pages. Something
like
/* allocate page-size multiples for mmap */
vzalloc(PAGE_ALIGN(screen_size))
I just thought about your instruction at here, thanks!
But it is already page size aligned if we don't tough it.
It is guaranteed by the GEM memory manger,
so a previous patch tested by me, is turn out to be a extremely correct?
We exposed a page size aligned buffer(even though it is larger than needed)
is actually for mmap ?
mmap() is always page aligned, because that's the smallest size the cpu
pagetables can map. So there's fundamentally always a bit of memory at the
end of the buffer which logically is not part of the framebuffer memory.
And somehow we need to handle that to make sure we don't overflow.
-Daniel
Yeah, buffer allocating should be page size aligned,
A single page share the same caching property.
fbdev test use the `smem_len` member of `fix_info` to know the true size
of the shadow screen buffer.
Exposing a large one actually allow the test writing to somewhere beyond
the logically visible area.
I need to learn more and testing more to verify if there are still
risks, I'll take a look.
Thanks for sharing the knowledge.
It has not been a bug so far because vzalloc() always returns full pages
IIRC. It's still worth fixing.
Best regards
Thomas
if (!screen_buffer) {
ret = -ENOMEM;