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

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Message-ID: <20150120165127.GG30656@x1>
Date:	Tue, 20 Jan 2015 16:51:27 +0000
From:	Lee Jones <lee.jones@...aro.org>
To:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
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

On Tue, 20 Jan 2015, Javier Martinez Canillas wrote:

> 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?

Yes: Acked-by: Lee Jones <lee.jones@...aro.org>

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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