From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pasi =?iso-8859-1?Q?K=E4rkk=E4inen?= Subject: Re: [PATCH] drm/nouveau: avoid null deref on bad arguments to nouveau_vma_getmap Date: Wed, 25 Sep 2013 17:41:52 +0300 Message-ID: <20130925144152.GK2924@reaktio.net> References: <1377130214-17522-1-git-send-email-imirkin@alum.mit.edu> <5215B9E8.5080108@canonical.com> <5226DA41.5060203@canonical.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: Content-Disposition: inline In-Reply-To: <5226DA41.5060203@canonical.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dri-devel-bounces+sf-dri-devel=m.gmane.org@lists.freedesktop.org Errors-To: dri-devel-bounces+sf-dri-devel=m.gmane.org@lists.freedesktop.org To: Maarten Lankhorst Cc: "nouveau@lists.freedesktop.org" , "dri-devel@lists.freedesktop.org" , Ben Skeggs List-Id: nouveau.vger.kernel.org Hello, On Wed, Sep 04, 2013 at 08:59:13AM +0200, Maarten Lankhorst wrote: > Op 04-09-13 05:41, Ben Skeggs schreef: > > On Thu, Aug 22, 2013 at 5:12 PM, Maarten Lankhorst > > 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 n= ot > >>> 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=3D64774 > >>> > >>> Reported-by: Pasi K=E4rkk=E4inen > >>> Tested-by: Pasi K=E4rkk=E4inen > >>> Signed-off-by: Ilia Mirkin > >>> Cc: # 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 sur= e :) > >> Not it really isn't appropriate.. > >> > >> You'd have to call call nouveau_vm_map_sg_table instead, the only plac= e 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/d= rm/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_devic= e *dev, > >> { > >> struct nouveau_framebuffer *nouveau_fb; > >> struct drm_gem_object *gem; > >> + struct nouveau_bo *nvbo; > >> int ret =3D -ENOMEM; > >> > >> gem =3D drm_gem_object_lookup(dev, file_priv, mode_cmd->handle= s[0]); > >> if (!gem) > >> return ERR_PTR(-ENOENT); > >> > >> + nvbo =3D nouveau_gem_object(gem); > >> + if (!(nvbo->valid_domains & NOUVEAU_GEM_DOMAIN_VRAM)) { > >> + nv_warn(nouveau_drm(dev), "Trying to create a fb in vr= am with" > >> + " valid_domains=3D%08x\n", nvbo->valid_domains= ); > >> + ret =3D -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 othe= r places that attempt to move buffers to VRAM though, so it's probably harm= less. > Ben/Maarten: Are you guys planning to take a look at this and submit anothe= r patch, or.. ? = I tested the two earlier patches from this thread, and they both fixed the = problem (hard kernel crash). I'm hoping this bug could be finally solved in the kernel.. Thanks, -- Pasi