[PATCH] drm/nouveau: avoid null deref on bad arguments to nouveau_vma_getmap

[Maarten Lankhorst]

Op 04-09-13 05:41, Ben Skeggs schreef:
> On Thu, Aug 22, 2013 at 5:12 PM, Maarten Lankhorst
> <maarten.lankhorst at canonical.com> wrote:
>> Op 22-08-13 02:10, Ilia Mirkin schreef:
>>> The code expects non-VRAM mem nodes to have a pages list. If that's not
>>> set, it will do a null deref down the line. Warn on that condition and
>>> return an error.
>>>
>>> See https://bugs.freedesktop.org/show_bug.cgi?id=64774
>>>
>>> Reported-by: Pasi Kärkkäinen <pasik at iki.fi>
>>> Tested-by: Pasi Kärkkäinen <pasik at iki.fi>
>>> Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
>>> Cc: <stable at vger.kernel.org> # 3.8+
>>> ---
>>>
>>> I don't exactly understand what's going on, but this is just a
>>> straightforward way to avoid a null deref that you see happens in the
>>> bug. I haven't figured out the root cause of this, but it's getting
>>> well into the "I have no idea how TTM works" space. However this seems
>>> like a bit of defensive programming -- nouveau_vm_map_sg will pass
>>> node->pages as a list down, which will be dereferenced by
>>> nvc0_vm_map_sg. Perhaps the other arguments should make that
>>> dereferencing not happen, but it definitely was happening here, as you
>>> can see in the bug.
>>>
>>> Ben/Maarten, I'll let you judge whether this check is appropriate,
>>> since like I hope I was able to convey above, I'm just not really sure :)
>> Not it really isn't appropriate..
>>
>> You'd have to call call nouveau_vm_map_sg_table instead, the only place that doesn't handle that correctly
>> is where it's not expected to be called.
>>
>> Here, have a completely untested patch to fix things...
>>
>> diff --git a/drivers/gpu/drm/nouveau/nouveau_display.c b/drivers/gpu/drm/nouveau/nouveau_display.c
>> --- a/drivers/gpu/drm/nouveau/nouveau_display.c
>> +++ b/drivers/gpu/drm/nouveau/nouveau_display.c
>> @@ -138,17 +143,26 @@ nouveau_user_framebuffer_create(struct drm_device *dev,
>>  {
>>         struct nouveau_framebuffer *nouveau_fb;
>>         struct drm_gem_object *gem;
>> +       struct nouveau_bo *nvbo;
>>         int ret = -ENOMEM;
>>
>>         gem = drm_gem_object_lookup(dev, file_priv, mode_cmd->handles[0]);
>>         if (!gem)
>>                 return ERR_PTR(-ENOENT);
>>
>> +       nvbo = nouveau_gem_object(gem);
>> +       if (!(nvbo->valid_domains & NOUVEAU_GEM_DOMAIN_VRAM)) {
>> +               nv_warn(nouveau_drm(dev), "Trying to create a fb in vram with"
>> +                       " valid_domains=%08x\n", nvbo->valid_domains);
>> +               ret = -EINVAL;
>> +               goto err_unref;
>> +       }
>> +
> Definitely the right idea, we can't handle this case right now.
> However, we may someday want/need to be able to scan out of system
> memory, so this is the wrong place.
>
> I suspect the correct thing to do (which'll also handle the
> "defensive" part) is to bail in nouveau_bo_move() on attempts to move
> a DMA-BUF backed object into VRAM.
>
> Sound OK?
>
If it has a WARN_ON or something that would be ok, I didn't find any other places that attempt to move buffers to VRAM though, so it's probably harmless.

When looking into this bug I noticed that nouveau_bo_vma_add needs to have a check for nvbo->page_shift == vma->vm->vmm->spg_shift,
and only if the check is true it should map the page in TTM_PL_TT. Patch below.
Should probably also be cc'd to stable.

~Maarten

diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c b/drivers/gpu/drm/nouveau/nouveau_bo.c
index 89b992e..355a1b7 100644
--- a/drivers/gpu/drm/nouveau/nouveau_bo.c
+++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
@@ -1560,7 +1560,8 @@ nouveau_bo_vma_add(struct nouveau_bo *nvbo, struct nouveau_vm *vm,
 
 	if (nvbo->bo.mem.mem_type == TTM_PL_VRAM)
 		nouveau_vm_map(vma, nvbo->bo.mem.mm_node);
-	else if (nvbo->bo.mem.mem_type == TTM_PL_TT) {
+	else if (nvbo->bo.mem.mem_type == TTM_PL_TT &&
+		 nvbo->page_shift == vma->vm->vmm->spg_shift) {
 		if (node->sg)
 			nouveau_vm_map_sg_table(vma, 0, size, node);
 		else