linux-kernel - Re: [PATCH] crypto: gcm

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Message-ID: <VI1PR0402MB3485D7664F87D8C38FA8FD5C98190@VI1PR0402MB3485.eurprd04.prod.outlook.com>
Date:   Fri, 31 May 2019 05:22:50 +0000
From:   Horia Geanta <horia.geanta@....com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
CC:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Eric Biggers <ebiggers@...nel.org>,
        Iuliana Prodan <iuliana.prodan@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH] crypto: gcm - fix cacheline sharing

On 5/30/2019 4:26 PM, Herbert Xu wrote:
> On Thu, May 30, 2019 at 01:18:34PM +0000, Horia Geanta wrote:
>>
>> I guess there are only two options:
>> -either cache line sharing is avoided OR
>> -users need to be *aware* they are sharing the cache line and some rules /
>> assumptions are in place on how to safely work on the data
> 
> No there is a third option and it's very simple:
> 
I see this as the 2nd option.

> You must only access the virtual addresses given to you before DMA
> mapping or after DMA unmapping.
> 
Unless it's clearly defined *which* virtual addresses mustn't be accessed,
things won't work properly.
In theory, any two objects could share a cache line. We can't just stop all
memory accesses from CPU while a peripheral is busy.

Thanks,
Horia