linux-kernel - Re: [2/6] uaccess: add probe_kernel

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Message-Id: <20080211084627.d67b4347.randy.dunlap@oracle.com>
Date:	Mon, 11 Feb 2008 08:46:27 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jan Kiszka <jan.kiszka@....de>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@....com.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Wessel <jason.wessel@...driver.com>
Subject: Re: [2/6] uaccess: add probe_kernel_write()

On Sun, 10 Feb 2008 21:05:40 +0100 Ingo Molnar wrote:

> Subject: uaccess: add probe_kernel_write()
> From: Ingo Molnar <mingo@...e.hu>
> 
> add probe_kernel_read() and probe_kernel_write().
> 
> Uninlined and restricted to kernel range memory only, as suggested
> by Linus.
> 
> Signed-off-by: Ingo Molnar <mingo@...e.hu>
> ---
>  include/linux/uaccess.h |   22 ++++++++++++++++++++++
>  mm/Makefile             |    2 +-
>  mm/maccess.c            |   46 ++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 69 insertions(+), 1 deletion(-)
> 
> Index: linux-kgdb.q/include/linux/uaccess.h
> ===================================================================
> --- linux-kgdb.q.orig/include/linux/uaccess.h
> +++ linux-kgdb.q/include/linux/uaccess.h
> @@ -84,4 +84,26 @@ static inline unsigned long __copy_from_
>  		ret;					\
>  	})
>  
> +/*
> + * probe_kernel_read(): safely attempt to read from a location

Please insert a hyphen/dash/'-' between function name and its
short description on the line above and on other similar lines.

Documentation/kernel-doc-nano-HOWTO.txt .

> + * @dst: pointer to the buffer that shall take the data
> + * @src: address to read from
> + * @size: size of the data chunk
> + *
> + * Safely read from address @src to the buffer at @dst.  If a kernel fault
> + * happens, handle that and return -EFAULT.
> + */
> +extern long probe_kernel_read(void *dst, void *src, size_t size);
> +
> +/*
> + * probe_kernel_write(): safely attempt to write to a location
> + * @dst: address to write to
> + * @src: pointer to the data that shall be written
> + * @size: size of the data chunk
> + *
> + * Safely write to address @dst from the buffer at @src.  If a kernel fault
> + * happens, handle that and return -EFAULT.
> + */
> +extern long probe_kernel_write(void *dst, void *src, size_t size);
> +
>  #endif		/* __LINUX_UACCESS_H__ */

> Index: linux-kgdb.q/mm/maccess.c
> ===================================================================
> --- /dev/null
> +++ linux-kgdb.q/mm/maccess.c
> @@ -0,0 +1,46 @@
> +/*
> + * Access kernel memory without faulting.
> + */
> +#include <linux/uaccess.h>
> +#include <linux/mm.h>
> +
> +/**
> + * probe_kernel_read(): safely attempt to read from a location
> + * @dst: pointer to the buffer that shall take the data
> + * @src: address to read from
> + * @size: size of the data chunk
> + *
> + * Safely read from address @src to the buffer at @dst.  If a kernel fault
> + * happens, handle that and return -EFAULT.
> + */
> +long probe_kernel_read(void *dst, void *src, size_t size)
> +{
> +	long ret;
> +
> +	pagefault_disable();
> +	ret = __copy_from_user_inatomic(dst,
> +			(__force const void __user *)src, size);
> +	pagefault_enable();
> +
> +	return ret ? -EFAULT : 0;
> +}
> +
> +/**
> + * probe_kernel_write(): safely attempt to write to a location
> + * @dst: address to write to
> + * @src: pointer to the data that shall be written
> + * @size: size of the data chunk
> + *
> + * Safely write to address @dst from the buffer at @src.  If a kernel fault
> + * happens, handle that and return -EFAULT.
> + */
> +long probe_kernel_write(void *dst, void *src, size_t size)
> +{
> +	long ret;
> +
> +	pagefault_disable();
> +	ret = __copy_to_user_inatomic((__force void __user *)dst, src, size);
> +	pagefault_enable();
> +
> +	return ret ? -EFAULT : 0;
> +}

---
~Randy
--
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