linux-kernel - Re: [PATCH RESEND v2 2/7] mfd: cros_ec: Add char dev and virtual dev pointers

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Message-ID: <54BE8615.7070708@collabora.co.uk>
Date:	Tue, 20 Jan 2015 17:45:09 +0100
From:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
To:	Lee Jones <lee.jones@...aro.org>
CC:	Olof Johansson <olof@...om.net>,
	Doug Anderson <dianders@...omium.org>,
	Bill Richardson <wfrichar@...omium.org>,
	Simon Glass <sjg@...gle.com>,
	Gwendal Grignou <gwendal@...gle.com>,
	Jonathan Corbet <corbet@....net>,
	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND v2 2/7] mfd: cros_ec: Add char dev and virtual
 dev pointers

Hello Lee,

On 01/20/2015 05:36 PM, Lee Jones wrote:
>> > 
>> > Is this safe?  Are you sure it's okay to provide an interface from
>> > userspace to read (kernel?) memory?
>> >
>> 
>> This interface is not to read any kernel memory but only the memory mapped
>> I/O region for the Low Pin Count (LPC) bus. So user-space only can choose
>> and offset and a number of bytes using the CROS_EC_DEV_IOCRDMEM ioctl cmd
>> which uses the following structure as argument:
>> 
>> /*
>>  * @offset: within EC_LPC_ADDR_MEMMAP region
>>  * @bytes: number of bytes to read. zero means "read a string" (including '\0')
>>  *         (at most only EC_MEMMAP_SIZE bytes can be read)
>>  * @buffer: where to store the result
>>  * ioctl returns the number of bytes read, negative on error
>>  */
>> struct cros_ec_readmem {
>>         uint32_t offset;
>>         uint32_t bytes;
>>         uint8_t buffer[EC_MEMMAP_SIZE];
>> };
>> 
>> The cros_ec_lpc_readmem() handler that the function pointer is set only
>> reads bytes from EC_LPC_ADDR_MEMMAP + offset if offset < EC_MEMMAP_SIZE
>> and the data is copied to the user-space buffer from the structure passed
>> as argument with copy_to_user().
>> 
>> So in that sense is similar to the spidev or i2c-dev interfaces that are
>> used to access these buses from user-space.
> 
> Very well.  The purpose of my question was to be provocative and to
> make you think about the interface.  As long as you're sure it can't
> be abused, then I'm happy.
> 

Ok, thanks a lot. Does it mean I've your Acked-by for this patch too?

Best regards,
Javier
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