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

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Date:   Wed, 24 Jan 2018 02:19:27 -0800
From:   Laura Abbott <labbott@...hat.com>
To:     Liam Mark <lmark@...eaurora.org>,
        Sumit Semwal <sumit.semwal@...aro.org>
Cc:     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 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,
Laura

>   	table = kmalloc(sizeof(*table), GFP_KERNEL);
>   	if (!table)
>   		goto err;
>