Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH v2] staging: android: ion: Zero CMA allocated memory
To:     Liam Mark <lmark@codeaurora.org>,
        Sumit Semwal <sumit.semwal@linaro.org>
Cc:     linux-kernel@vger.kernel.org, devel@driverdev.osuosl.org,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        linaro-mm-sig@lists.linaro.org
References: <alpine.DEB.2.02.1801220940500.8950@lmark-linux.qualcomm.com>
From:   Laura Abbott <labbott@redhat.com>
Message-ID: <d347fc8a-02c6-d24e-dad5-3781c6330e0d@redhat.com>
Date:   Wed, 24 Jan 2018 02:19:27 -0800
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.5.2
MIME-Version: 1.0
In-Reply-To: <alpine.DEB.2.02.1801220940500.8950@lmark-linux.qualcomm.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@codeaurora.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;
>