linux-kernel - Re: [PATCH v2] drm/radeon/radeon_display: Decrease the size of allocated memory

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Message-ID: <CADnq5_OsJ+VxY9z_iqOscvWAoRqK2hZ0thUOHtBzhfo3De4EoA@mail.gmail.com>
Date: Mon, 8 Apr 2024 16:05:43 -0400
From: Alex Deucher <alexdeucher@...il.com>
To: Christian König <christian.koenig@....com>
Cc: Erick Archer <erick.archer@...look.com>, Alex Deucher <alexander.deucher@....com>, 
	"Pan, Xinhui" <Xinhui.Pan@....com>, David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
	"Gustavo A. R. Silva" <gustavoars@...nel.org>, Kees Cook <keescook@...omium.org>, 
	amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org, 
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] drm/radeon/radeon_display: Decrease the size of
 allocated memory

On Mon, Apr 1, 2024 at 8:35 AM Christian König <christian.koenig@....com> wrote:
>
> Am 30.03.24 um 17:34 schrieb Erick Archer:
> > This is an effort to get rid of all multiplications from allocation
> > functions in order to prevent integer overflows [1] [2].
> >
> > In this case, the memory allocated to store RADEONFB_CONN_LIMIT pointers
> > to "drm_connector" structures can be avoided. This is because this
> > memory area is never accessed.
> >
> > Also, in the kzalloc function, it is preferred to use sizeof(*pointer)
> > instead of sizeof(type) due to the type of the variable can change and
> > one needs not change the former (unlike the latter).
> >
> > At the same time take advantage to remove the "#if 0" block, the code
> > where the removed memory area was accessed, and the RADEONFB_CONN_LIMIT
> > constant due to now is never used.
> >
> > Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments [1]
> > Link: https://github.com/KSPP/linux/issues/160 [2]
> > Signed-off-by: Erick Archer <erick.archer@...look.com>
>
> Well in general we don't do any new feature development any more for the
> radeon driver.
>
> But this cleanup looks so straight forward that the risk of breaking
> something is probably very low.
>
> Acked-by from my side, but Alex should probably take a look as well.

I can't remember why that was done that way.  Maybe some leftover from
the early KMS days before we finalized the fbdev interactions?
Anyway, patch applied.  Thanks.

Alex

>
> Regards,
> Christian.
>
> > ---
> > Changes in v2:
> > - Rebase against linux-next.
> >
> > Previous versions:
> > v1 -> https://lore.kernel.org/linux-hardening/20240222180431.7451-1-erick.archer@gmx.com/
> >
> > Hi everyone,
> >
> > Any comments would be greatly appreciated. The first version was
> > not commented.
> >
> > Thanks,
> > Erick
> > ---
> >   drivers/gpu/drm/radeon/radeon.h         | 1 -
> >   drivers/gpu/drm/radeon/radeon_display.c | 8 +-------
> >   2 files changed, 1 insertion(+), 8 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/radeon/radeon.h b/drivers/gpu/drm/radeon/radeon.h
> > index 3e5ff17e3caf..0999c8eaae94 100644
> > --- a/drivers/gpu/drm/radeon/radeon.h
> > +++ b/drivers/gpu/drm/radeon/radeon.h
> > @@ -132,7 +132,6 @@ extern int radeon_cik_support;
> >   /* RADEON_IB_POOL_SIZE must be a power of 2 */
> >   #define RADEON_IB_POOL_SIZE                 16
> >   #define RADEON_DEBUGFS_MAX_COMPONENTS               32
> > -#define RADEONFB_CONN_LIMIT                  4
> >   #define RADEON_BIOS_NUM_SCRATCH                     8
> >
> >   /* internal ring indices */
> > diff --git a/drivers/gpu/drm/radeon/radeon_display.c b/drivers/gpu/drm/radeon/radeon_display.c
> > index efd18c8d84c8..5f1d24d3120c 100644
> > --- a/drivers/gpu/drm/radeon/radeon_display.c
> > +++ b/drivers/gpu/drm/radeon/radeon_display.c
> > @@ -683,7 +683,7 @@ static void radeon_crtc_init(struct drm_device *dev, int index)
> >       struct radeon_device *rdev = dev->dev_private;
> >       struct radeon_crtc *radeon_crtc;
> >
> > -     radeon_crtc = kzalloc(sizeof(struct radeon_crtc) + (RADEONFB_CONN_LIMIT * sizeof(struct drm_connector *)), GFP_KERNEL);
> > +     radeon_crtc = kzalloc(sizeof(*radeon_crtc), GFP_KERNEL);
> >       if (radeon_crtc == NULL)
> >               return;
> >
> > @@ -709,12 +709,6 @@ static void radeon_crtc_init(struct drm_device *dev, int index)
> >       dev->mode_config.cursor_width = radeon_crtc->max_cursor_width;
> >       dev->mode_config.cursor_height = radeon_crtc->max_cursor_height;
> >
> > -#if 0
> > -     radeon_crtc->mode_set.crtc = &radeon_crtc->base;
> > -     radeon_crtc->mode_set.connectors = (struct drm_connector **)(radeon_crtc + 1);
> > -     radeon_crtc->mode_set.num_connectors = 0;
> > -#endif
> > -
> >       if (rdev->is_atom_bios && (ASIC_IS_AVIVO(rdev) || radeon_r4xx_atom))
> >               radeon_atombios_init_crtc(dev, radeon_crtc);
> >       else
>