[PATCH] drm/nouveau/acr: Fix undefined behavior in nvkm_acr_hsfw_load_bl()

[Kangjie Lu]

On Fri, Jan 28, 2022 at 1:58 PM Karol Herbst <kherbst at redhat.com> wrote:
>
> On Fri, Jan 28, 2022 at 8:54 PM Alex Deucher <alexdeucher at gmail.com> wrote:
> >
> > On Fri, Jan 28, 2022 at 2:20 PM Lyude Paul <lyude at redhat.com> wrote:
> > >
> > > Sigh-thank you for catching this - I had totally forgot about the umn.edu ban.
> > > I pushed this already but I will go ahead and send a revert for this patch.
> > > Will cc you on it as well.
> >
> > This seems short-sighted.  If the patch is valid I see no reason to
> > not accept it.  I'm not trying to downplay the mess umn got into, but
> > as long as the patch is well scrutinized and fixes a valid issue, it
> > should be applied rather than leaving potential bugs in place.
> >
> > Alex
> >
>
> Even though knowing that malicious code can be introduced via
> perfectly fine looking patches, and sometimes one will never spot the
> problem, this patch isn't all that bad tbh.
>
> So should we reject patches out of "policies" or should we just be
> extra careful? But not addressing the concerns as Greg pointed out is
> also kind of a bad move, but also not knowing what the state of
> resolving this mess is anyway.


Seeing some discussion here, I feel I owe you some quick updates on
the state. We sent three testing patches in August 2020, which is a
serious mistake. We never did that again and will never do that again.
All other patches including recent ones were sent to fix real bugs,
not to introduce problems. Clearly, although most of the patches are
valid, some patches are still not good enough, but it is not about
malice. Fixing bugs in Linux isn't an easy task and takes so much
effort.

We did not ignore the concerns pointed out by Greg, and have seriously
taken some actions. For example, we explained how our static-analysis
tool found the bugs, and members in my research group have internally
cross-reviewed the found bugs. We sent these patches after contacting
Greg---I thought Greg allowed us to send patches, but also requested
us to work on the last process with our administration. Unfortunately,
the process has been slow during the pandemic, but I hope this can be
resolved soon. Of course, before this is resolved, we will not send
any more patches.




>
> >
> > >
> > > On Fri, 2022-01-28 at 11:18 +0100, Greg KH wrote:
> > > > On Tue, Jan 25, 2022 at 12:58:55AM +0800, Zhou Qingyang wrote:
> > > > > In nvkm_acr_hsfw_load_bl(), the return value of kmalloc() is directly
> > > > > passed to memcpy(), which could lead to undefined behavior on failure
> > > > > of kmalloc().
> > > > >
> > > > > Fix this bug by using kmemdup() instead of kmalloc()+memcpy().
> > > > >
> > > > > This bug was found by a static analyzer.
> > > > >
> > > > > Builds with 'make allyesconfig' show no new warnings,
> > > > > and our static analyzer no longer warns about this code.
> > > > >
> > > > > Fixes: 22dcda45a3d1 ("drm/nouveau/acr: implement new subdev to replace
> > > > > "secure boot"")
> > > > > Signed-off-by: Zhou Qingyang <zhou1615 at umn.edu>
> > > > > ---
> > > > > The analysis employs differential checking to identify inconsistent
> > > > > security operations (e.g., checks or kfrees) between two code paths
> > > > > and confirms that the inconsistent operations are not recovered in the
> > > > > current function or the callers, so they constitute bugs.
> > > > >
> > > > > Note that, as a bug found by static analysis, it can be a false
> > > > > positive or hard to trigger. Multiple researchers have cross-reviewed
> > > > > the bug.
> > > > >
> > > > >  drivers/gpu/drm/nouveau/nvkm/subdev/acr/hsfw.c | 9 +++++----
> > > > >  1 file changed, 5 insertions(+), 4 deletions(-)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/acr/hsfw.c
> > > > > b/drivers/gpu/drm/nouveau/nvkm/subdev/acr/hsfw.c
> > > > > index 667fa016496e..a6ea89a5d51a 100644
> > > > > --- a/drivers/gpu/drm/nouveau/nvkm/subdev/acr/hsfw.c
> > > > > +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/acr/hsfw.c
> > > > > @@ -142,11 +142,12 @@ nvkm_acr_hsfw_load_bl(struct nvkm_acr *acr, const
> > > > > char *name, int ver,
> > > > >
> > > > >         hsfw->imem_size = desc->code_size;
> > > > >         hsfw->imem_tag = desc->start_tag;
> > > > > -       hsfw->imem = kmalloc(desc->code_size, GFP_KERNEL);
> > > > > -       memcpy(hsfw->imem, data + desc->code_off, desc->code_size);
> > > > > -
> > > > > +       hsfw->imem = kmemdup(data + desc->code_off, desc->code_size,
> > > > > GFP_KERNEL);
> > > > >         nvkm_firmware_put(fw);
> > > > > -       return 0;
> > > > > +       if (!hsfw->imem)
> > > > > +               return -ENOMEM;
> > > > > +       else
> > > > > +               return 0;
> > > > >  }
> > > > >
> > > > >  int
> > > > > --
> > > > > 2.25.1
> > > > >
> > > >
> > > > As stated before, umn.edu is still not allowed to contribute to the
> > > > Linux kernel.  Please work with your administration to resolve this
> > > > issue.
> > > >
> > >
> > > --
> > > Cheers,
> > >  Lyude Paul (she/her)
> > >  Software Engineer at Red Hat
> > >
> >
>


--
Kangjie Lu
Assistant Professor
Department of Computer Science and Engineering
University of Minnesota
https://www-users.cs.umn.edu/~kjlu