linux-kernel - Re: [PATCH v2] staging: android: ion: Zero CMA allocated memory

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Message-ID: <alpine.DEB.2.02.1801241638130.13091@lmark-linux.qualcomm.com>
Date:   Wed, 24 Jan 2018 16:40:27 -0800 (PST)
From:   Liam Mark <lmark@...eaurora.org>
To:     Laura Abbott <labbott@...hat.com>
cc:     Sumit Semwal <sumit.semwal@...aro.org>,
        linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH v2] staging: android: ion: Zero CMA allocated memory

On Wed, 24 Jan 2018, Laura Abbott wrote:

> On 01/22/2018 09:46 AM, Liam Mark wrote:
> > Since commit 204f672255c2 ("staging: android: ion: Use CMA APIs directly")
> > the CMA API is now used directly and therefore the allocated memory is no
> > longer automatically zeroed.
> > 
> > Explicitly zero CMA allocated memory to ensure that no data is exposed to
> > userspace.
> > 
> > Fixes: 204f672255c2 ("staging: android: ion: Use CMA APIs directly")
> > Signed-off-by: Liam Mark <lmark@...eaurora.org>
> > ---
> > Changes in v2:
> >    - Clean up the commit message.
> >    - Add 'Fixes:'
> > 
> >   drivers/staging/android/ion/ion_cma_heap.c | 2 ++
> >   1 file changed, 2 insertions(+)
> > 
> > diff --git a/drivers/staging/android/ion/ion_cma_heap.c
> > b/drivers/staging/android/ion/ion_cma_heap.c
> > index 86196ffd2faf..91a98785607a 100644
> > --- a/drivers/staging/android/ion/ion_cma_heap.c
> > +++ b/drivers/staging/android/ion/ion_cma_heap.c
> > @@ -51,6 +51,8 @@ static int ion_cma_allocate(struct ion_heap *heap, struct
> > ion_buffer *buffer,
> >   	if (!pages)
> >   		return -ENOMEM;
> > 
> > +	memset(page_address(pages), 0, size);
> > +
> 
> This won't work for highmem pages. You need to zero by page via
> kmap_atomic in that case. You can use PageHighMem to separate the
> paths.

Thanks for catching that, I will update the patch.

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