[Intel-gfx] [PATCH 2/2] drm/i915: consolidate 2big error checking for object sizes

[Matthew Auld]

On Fri, 22 Jan 2021 at 17:43, Chris Wilson <chris at chris-wilson.co.uk> wrote:
>
> Quoting Matthew Auld (2021-01-22 17:35:46)
> > Throw it into a simple helper, and throw a warning if we encounter an
> > object which has been initialised with an object size that exceeds our
> > limit of INT_MAX pages.
> >
> > Suggested-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> > ---
> >  drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c  |  9 +------
> >  drivers/gpu/drm/i915/gem/i915_gem_object.c  |  2 ++
> >  drivers/gpu/drm/i915/gem/i915_gem_object.h  | 26 +++++++++++++++++++++
> >  drivers/gpu/drm/i915/gem/i915_gem_region.c  | 12 +---------
> >  drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 16 +------------
> >  5 files changed, 31 insertions(+), 34 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> > index dc11497f830b..5cc8a0b2387f 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> > @@ -244,14 +244,7 @@ struct drm_gem_object *i915_gem_prime_import(struct drm_device *dev,
> >                 }
> >         }
> >
> > -       /*
> > -        * XXX: There is a prevalence of the assumption that we fit the
> > -        * object's page count inside a 32bit _signed_ variable. Let's document
> > -        * this and catch if we ever need to fix it. In the meantime, if you do
> > -        * spot such a local variable, please consider fixing!
> > -        */
> > -
> > -       if (dma_buf->size >> PAGE_SHIFT > INT_MAX)
> > +       if (i915_gem_object_size_2big(dma_buf->size))
> >                 return ERR_PTR(-E2BIG);
> >
> >         /* need to attach */
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c
> > index 70f798405f7f..d3702ea8c6aa 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c
> > @@ -62,6 +62,8 @@ void i915_gem_object_init(struct drm_i915_gem_object *obj,
> >                           const struct drm_i915_gem_object_ops *ops,
> >                           struct lock_class_key *key)
> >  {
> > +       GEM_CHECK_SIZE_OVERFLOW(obj->base.size);
> > +
> >         __mutex_init(&obj->mm.lock, ops->name ?: "obj->mm.lock", key);
> >
> >         spin_lock_init(&obj->vma.lock);
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> > index d0ae834d787a..d9cef56533ca 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_object.h
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> > @@ -16,6 +16,32 @@
> >  #include "i915_gem_gtt.h"
> >  #include "i915_vma_types.h"
> >
> > +/*
> > + * XXX: There is a prevalence of the assumption that we fit the
> > + * object's page count inside a 32bit _signed_ variable. Let's document
> > + * this and catch if we ever need to fix it. In the meantime, if you do
> > + * spot such a local variable, please consider fixing!
> > + *
> > + * Aside from our own locals (for which we have no excuse!):
> > + * - sg_table embeds unsigned int for num_pages
> > + * - get_user_pages*() mixed ints with longs
> > + */
> > +#define GEM_CHECK_SIZE_OVERFLOW(sz) \
> > +       GEM_WARN_ON((sz) >> PAGE_SHIFT > INT_MAX)
> > +
> > +static inline bool i915_gem_object_size_2big(u64 size)
> > +{
> > +       struct drm_i915_gem_object *obj;
> > +
> > +       if (size >> PAGE_SHIFT > INT_MAX)
> > +               return true;
>
> Macro here^
>
> Make it easy to grep, everybody gets a warning as a reminder to fix it.
> And a prize to whoever does manage to trigger the warning.

But this code is user triggable, like with igt("create-massive")? What
am I missing?


>
> > +
> > +       if (overflows_type(size, obj->base.size))
> > +               return true;
> > +
> > +       return false;
> > +}
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