Re: [PATCH 2/2] nouveau/dmem: Fix memory leak in `migrate_to_ram` upon copy error

[Yonatan Maman]

On 30/09/2024 14:20, Danilo Krummrich wrote:
> External email: Use caution opening links or attachments
>
>
> On Mon, Sep 23, 2024 at 01:54:58PM +0000, Yonatan Maman wrote:
> > A copy push command might fail, causing `migrate_to_ram` to return a
> > dirty HIGH_USER page to the user.
> >
> > This exposes a security vulnerability in the nouveau driver. To prevent
> > memory leaks in `migrate_to_ram` upon a copy error, allocate a zero
> > page for the destination page.
>
> So, you refer to the case where this function fails in nouveau_dmem_copy_one()?
>
> If so, can you please explain why adding __GFP_ZERO to alloc_page_vma() helps
> with that?

The nouveau_dmem_copy_one function ensures that the copy push command is 
sent to the device firmware but does not track whether it was executed 
successfully.

In the case of a copy error (e.g., firmware or hardware error), the 
command will be sent in the firmware channel, and nouveau_dmem_copy_one 
might succeed, as well as the migrate_to_ram function. Thus, a dirty 
page could be returned to the user.

It’s important to note that we attempted to use nouveau_fence_wait 
status to handle migration errors, but it does not catch all error types.

To avoid this vulnerability, we allocate a zero page. So that, in case 
of an error, a non-dirty (zero) page will be returned to the user.

> > Signed-off-by: Yonatan Maman <Ymaman@xxxxxxxxxx>
> > Signed-off-by: Gal Shalom <GalShalom@xxxxxxxxxx>
>
> Since this is a bug, please also add a 'Fixes' tag, CC stable and add a
> 'Co-developed-by' tag if appropriate.

sure, thanks, I will add, and push it as V2 patch-series.
> > ---
> >   drivers/gpu/drm/nouveau/nouveau_dmem.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> > index 6fb65b01d778..097bd3af0719 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> > @@ -193,7 +193,7 @@ static vm_fault_t nouveau_dmem_migrate_to_ram(struct vm_fault *vmf)
> >        if (!spage || !(src & MIGRATE_PFN_MIGRATE))
> >                goto done;
> >
> > -     dpage = alloc_page_vma(GFP_HIGHUSER, vmf->vma, vmf->address);
> > +     dpage = alloc_page_vma(GFP_HIGHUSER | __GFP_ZERO, vmf->vma, vmf->address);
> >        if (!dpage)
> >                goto done;
> >
> > --
> > 2.34.1