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

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Date: Mon, 1 Apr 2024 14:35:38 +0200
From: Christian König <christian.koenig@....com>
To: 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>
Cc: 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

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.

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