linux-kernel - Re: [PATCH 3/5] drm/mediatek: Add initialization for mtk_gem

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Date:   Tue, 13 Jun 2023 07:20:19 +0000
From:   Jason-JH Lin (林睿祥) 
        <Jason-JH.Lin@...iatek.com>
To:     CK Hu (胡俊光) <ck.hu@...iatek.com>,
        "chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        Singo Chang (張興國) 
        <Singo.Chang@...iatek.com>,
        Jason-ch Chen (陳建豪) 
        <Jason-ch.Chen@...iatek.com>,
        Shawn Sung (宋孝謙) 
        <Shawn.Sung@...iatek.com>,
        Nancy Lin (林欣螢) <Nancy.Lin@...iatek.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Project_Global_Chrome_Upstream_Group 
        <Project_Global_Chrome_Upstream_Group@...iatek.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        Rex-BC Chen (陳柏辰) 
        <Rex-BC.Chen@...iatek.com>
Subject: Re: [PATCH 3/5] drm/mediatek: Add initialization for mtk_gem_obj

Hi CK,

Thanks for the reviews.

On Mon, 2023-06-12 at 08:27 +0000, CK Hu (胡俊光) wrote:
> Hi, Jason:
> 
> On Fri, 2023-04-07 at 14:46 +0800, Jason-JH.Lin wrote:
> > Calling mtk_gem_obj = kzalloc() which returns uninitialized memory,
> > because mtk_gem_obj is uninitialized.
> > 
> > It may cause using uninitialized value mtk_gem_obj->base.resv
> > when calling drm_gem_object_init().
> > 
> > So add initialization for mtk_gem_obj.
> 
> So weird, nacked by me.
> 
> Regards,
> CK
> 
I've checked the coverity issue:
1. alloc_fn: Calling kzalloc which returns uninitialized memory. 
2. assign: Assigning: mtk_gem_obj = kzalloc(424UL, 3264U), which points
to uninitialized data.
   mtk_gem_obj = kzalloc(sizeof(*mtk_gem_obj), GFP_KERNEL);

/include/linux/slab.h
733: static inline void *kzalloc(size_t size, gfp_t flags)
734: {
1. uninit_buffer: Call to kmalloc(size, flags | 0x100U) returns an
uninitialized buffer. [Note: The source code implementation of the
function has been overridden by a builtin model.]
2. return: Returning kmalloc(size, flags | 0x100U).


I think it may be a misjudgment to kzalloc returning an uninitialized
memory, so I'll drop this path.

Regards,
Jason-JH.Lin

> > 
> > Signed-off-by: Jason-JH.Lin <jason-jh.lin@...iatek.com>
> > Fixes: 119f5173628a ("drm/mediatek: Add DRM Driver for Mediatek SoC
> > MT8173.")
> > ---
> >  drivers/gpu/drm/mediatek/mtk_drm_gem.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> > b/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> > index a25b28d3ee90..9b8f72ed12e4 100644
> > --- a/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> > +++ b/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> > @@ -33,7 +33,7 @@ static const struct drm_gem_object_funcs
> > mtk_drm_gem_object_funcs = {
> >  static struct mtk_drm_gem_obj *mtk_drm_gem_init(struct drm_device
> > *dev,
> >  						unsigned long size)
> >  {
> > -	struct mtk_drm_gem_obj *mtk_gem_obj;
> > +	struct mtk_drm_gem_obj *mtk_gem_obj = NULL;
> >  	int ret;
> >  
> >  	size = round_up(size, PAGE_SIZE);