2018-09-01 12:22:11

by Jia-Ju Bai

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Subject: [PATCH] gpu: drm: drm_mm: Fix a sleep-in-atomic-context bug in show_leaks()

The driver may sleep with holding a spinlock.

The function call paths (from bottom to top) in Linux-4.16 are:

[FUNC] kmalloc(GFP_KERNEL)
drivers/gpu/drm/drm_mm.c, 130:
kmalloc in show_leaks
drivers/gpu/drm/drm_mm.c, 913:
show_leaks in drm_mm_takedown
drivers/gpu/drm/drm_vma_manager.c, 107:
drm_mm_takedown in drm_vma_offset_manager_destroy
drivers/gpu/drm/drm_vma_manager.c, 106:
_raw_write_lock in drm_vma_offset_manager_destroy

[FUNC] kmalloc(GFP_KERNEL)
drivers/gpu/drm/drm_mm.c, 130:
kmalloc in show_leaks
drivers/gpu/drm/drm_mm.c, 913:
show_leaks in drm_mm_takedown
drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c, 71:
drm_mm_takedown in amdgpu_vram_mgr_fini
drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c, 70:
spin_lock in amdgpu_vram_mgr_fini

[FUNC] kmalloc(GFP_KERNEL)
drivers/gpu/drm/drm_mm.c, 130:
kmalloc in show_leaks
drivers/gpu/drm/drm_mm.c, 913:
show_leaks in drm_mm_takedown
drivers/gpu/drm/ttm/ttm_bo_manager.c, 128:
drm_mm_takedown in ttm_bo_man_takedown
drivers/gpu/drm/ttm/ttm_bo_manager.c, 126:
spin_lock in ttm_bo_man_takedown

To fix this bug, GFP_KERNEL is replaced with GFP_ATOMIC.

This bug is found by my static analysis tool DSAC.

Signed-off-by: Jia-Ju Bai <[email protected]>
---
drivers/gpu/drm/drm_mm.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
index 3166026a1874..2486121a78d4 100644
--- a/drivers/gpu/drm/drm_mm.c
+++ b/drivers/gpu/drm/drm_mm.c
@@ -127,7 +127,7 @@ static void show_leaks(struct drm_mm *mm)
unsigned long entries[STACKDEPTH];
char *buf;

- buf = kmalloc(BUFSZ, GFP_KERNEL);
+ buf = kmalloc(BUFSZ, GFP_ATOMIC);
if (!buf)
return;

--
2.17.0



2018-09-01 12:34:17

by Chris Wilson

[permalink] [raw]
Subject: Re: [PATCH] gpu: drm: drm_mm: Fix a sleep-in-atomic-context bug in show_leaks()

Quoting Jia-Ju Bai (2018-09-01 13:20:41)
> The driver may sleep with holding a spinlock.
>
> The function call paths (from bottom to top) in Linux-4.16 are:
>
> [FUNC] kmalloc(GFP_KERNEL)
> drivers/gpu/drm/drm_mm.c, 130:
> kmalloc in show_leaks
> drivers/gpu/drm/drm_mm.c, 913:
> show_leaks in drm_mm_takedown
> drivers/gpu/drm/drm_vma_manager.c, 107:
> drm_mm_takedown in drm_vma_offset_manager_destroy
> drivers/gpu/drm/drm_vma_manager.c, 106:
> _raw_write_lock in drm_vma_offset_manager_destroy
>
> [FUNC] kmalloc(GFP_KERNEL)
> drivers/gpu/drm/drm_mm.c, 130:
> kmalloc in show_leaks
> drivers/gpu/drm/drm_mm.c, 913:
> show_leaks in drm_mm_takedown
> drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c, 71:
> drm_mm_takedown in amdgpu_vram_mgr_fini
> drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c, 70:
> spin_lock in amdgpu_vram_mgr_fini
>
> [FUNC] kmalloc(GFP_KERNEL)
> drivers/gpu/drm/drm_mm.c, 130:
> kmalloc in show_leaks
> drivers/gpu/drm/drm_mm.c, 913:
> show_leaks in drm_mm_takedown
> drivers/gpu/drm/ttm/ttm_bo_manager.c, 128:
> drm_mm_takedown in ttm_bo_man_takedown
> drivers/gpu/drm/ttm/ttm_bo_manager.c, 126:
> spin_lock in ttm_bo_man_takedown
>
> To fix this bug, GFP_KERNEL is replaced with GFP_ATOMIC.

The bug are above, since those spinlocks do not protect the data and
imply use-after-free.
-Chris

2018-09-03 07:54:06

by Daniel Vetter

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Subject: Re: [PATCH] gpu: drm: drm_mm: Fix a sleep-in-atomic-context bug in show_leaks()

On Sat, Sep 01, 2018 at 01:32:54PM +0100, Chris Wilson wrote:
> Quoting Jia-Ju Bai (2018-09-01 13:20:41)
> > The driver may sleep with holding a spinlock.
> >
> > The function call paths (from bottom to top) in Linux-4.16 are:
> >
> > [FUNC] kmalloc(GFP_KERNEL)
> > drivers/gpu/drm/drm_mm.c, 130:
> > kmalloc in show_leaks
> > drivers/gpu/drm/drm_mm.c, 913:
> > show_leaks in drm_mm_takedown
> > drivers/gpu/drm/drm_vma_manager.c, 107:
> > drm_mm_takedown in drm_vma_offset_manager_destroy
> > drivers/gpu/drm/drm_vma_manager.c, 106:
> > _raw_write_lock in drm_vma_offset_manager_destroy
> >
> > [FUNC] kmalloc(GFP_KERNEL)
> > drivers/gpu/drm/drm_mm.c, 130:
> > kmalloc in show_leaks
> > drivers/gpu/drm/drm_mm.c, 913:
> > show_leaks in drm_mm_takedown
> > drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c, 71:
> > drm_mm_takedown in amdgpu_vram_mgr_fini
> > drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c, 70:
> > spin_lock in amdgpu_vram_mgr_fini
> >
> > [FUNC] kmalloc(GFP_KERNEL)
> > drivers/gpu/drm/drm_mm.c, 130:
> > kmalloc in show_leaks
> > drivers/gpu/drm/drm_mm.c, 913:
> > show_leaks in drm_mm_takedown
> > drivers/gpu/drm/ttm/ttm_bo_manager.c, 128:
> > drm_mm_takedown in ttm_bo_man_takedown
> > drivers/gpu/drm/ttm/ttm_bo_manager.c, 126:
> > spin_lock in ttm_bo_man_takedown
> >
> > To fix this bug, GFP_KERNEL is replaced with GFP_ATOMIC.
>
> The bug are above, since those spinlocks do not protect the data and
> imply use-after-free.

Adding amdgpu, since that's where the bug seems to be.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

2018-09-03 12:07:17

by Christian König

[permalink] [raw]
Subject: Re: [PATCH] gpu: drm: drm_mm: Fix a sleep-in-atomic-context bug in show_leaks()

Am 03.09.2018 um 09:52 schrieb Daniel Vetter:
> On Sat, Sep 01, 2018 at 01:32:54PM +0100, Chris Wilson wrote:
>> Quoting Jia-Ju Bai (2018-09-01 13:20:41)
>>> The driver may sleep with holding a spinlock.
>>>
>>> The function call paths (from bottom to top) in Linux-4.16 are:
>>>
>>> [FUNC] kmalloc(GFP_KERNEL)
>>> drivers/gpu/drm/drm_mm.c, 130:
>>> kmalloc in show_leaks
>>> drivers/gpu/drm/drm_mm.c, 913:
>>> show_leaks in drm_mm_takedown
>>> drivers/gpu/drm/drm_vma_manager.c, 107:
>>> drm_mm_takedown in drm_vma_offset_manager_destroy
>>> drivers/gpu/drm/drm_vma_manager.c, 106:
>>> _raw_write_lock in drm_vma_offset_manager_destroy
>>>
>>> [FUNC] kmalloc(GFP_KERNEL)
>>> drivers/gpu/drm/drm_mm.c, 130:
>>> kmalloc in show_leaks
>>> drivers/gpu/drm/drm_mm.c, 913:
>>> show_leaks in drm_mm_takedown
>>> drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c, 71:
>>> drm_mm_takedown in amdgpu_vram_mgr_fini
>>> drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c, 70:
>>> spin_lock in amdgpu_vram_mgr_fini
>>>
>>> [FUNC] kmalloc(GFP_KERNEL)
>>> drivers/gpu/drm/drm_mm.c, 130:
>>> kmalloc in show_leaks
>>> drivers/gpu/drm/drm_mm.c, 913:
>>> show_leaks in drm_mm_takedown
>>> drivers/gpu/drm/ttm/ttm_bo_manager.c, 128:
>>> drm_mm_takedown in ttm_bo_man_takedown
>>> drivers/gpu/drm/ttm/ttm_bo_manager.c, 126:
>>> spin_lock in ttm_bo_man_takedown
>>>
>>> To fix this bug, GFP_KERNEL is replaced with GFP_ATOMIC.
>> The bug are above, since those spinlocks do not protect the data and
>> imply use-after-free.
> Adding amdgpu, since that's where the bug seems to be.

When we have use after free we might have concurrent uses as well.

I think taking the lock here is probably a good idea if you don't want
to accidentally access freed memory in show_leaks.

So Chris change sounds valid to me.

Christian.

> -Daniel