linux-kernel - Re: [PATCH] lib/hexdump: introduce DUMP_PREFIX

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Message-ID: <X/wkMMiPPBAJb9+A@alley>
Date:   Mon, 11 Jan 2021 11:10:56 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Timur Tabi <timur@...i.org>
Cc:     torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Roman Fietze <roman.fietze@...na.com>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] lib/hexdump: introduce DUMP_PREFIX_UNHASHED for unhashed
 addresses

Adding Kees into CC because it is security related.
Adding Andrew into CC because he usually takes patches for hexdump.

On Wed 2021-01-06 15:35:47, Timur Tabi wrote:
> Hashed addresses are useless in hexdumps unless you're comparing
> with other hashed addresses, which is unlikely.  However, there's
> no need to break existing code, so introduce a new prefix type
> that prints unhashed addresses.
> 
> Signed-off-by: Timur Tabi <timur@...i.org>
> Cc: Roman Fietze <roman.fietze@...na.com>

I agree that there should be way to print the real address.

And it is sane to add a new mode so that the current
users stay hashed.

Reviewed-by: Petr Mladek <pmladek@...e.com>

> ---
>  include/linux/printk.h | 3 ++-
>  lib/hexdump.c          | 9 +++++++--
>  2 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/printk.h b/include/linux/printk.h
> index fe7eb2351610..5d833bad785c 100644
> --- a/include/linux/printk.h
> +++ b/include/linux/printk.h
> @@ -567,7 +567,8 @@ extern const struct file_operations kmsg_fops;
>  enum {
>  	DUMP_PREFIX_NONE,
>  	DUMP_PREFIX_ADDRESS,
> -	DUMP_PREFIX_OFFSET
> +	DUMP_PREFIX_OFFSET,
> +	DUMP_PREFIX_UNHASHED,
>  };
>  extern int hex_dump_to_buffer(const void *buf, size_t len, int rowsize,
>  			      int groupsize, char *linebuf, size_t linebuflen,
> diff --git a/lib/hexdump.c b/lib/hexdump.c
> index 9301578f98e8..b5acfc4168a8 100644
> --- a/lib/hexdump.c
> +++ b/lib/hexdump.c
> @@ -211,8 +211,9 @@ EXPORT_SYMBOL(hex_dump_to_buffer);
>   * @level: kernel log level (e.g. KERN_DEBUG)
>   * @prefix_str: string to prefix each line with;
>   *  caller supplies trailing spaces for alignment if desired
> - * @prefix_type: controls whether prefix of an offset, address, or none
> - *  is printed (%DUMP_PREFIX_OFFSET, %DUMP_PREFIX_ADDRESS, %DUMP_PREFIX_NONE)
> + * @prefix_type: controls whether prefix of an offset, hashed address,
> + *  unhashed address, or none is printed (%DUMP_PREFIX_OFFSET,
> + *  %DUMP_PREFIX_ADDRESS, %DUMP_PREFIX_UNHASHED, %DUMP_PREFIX_NONE)
>   * @rowsize: number of bytes to print per line; must be 16 or 32
>   * @groupsize: number of bytes to print at a time (1, 2, 4, 8; default = 1)
>   * @buf: data blob to dump
> @@ -256,6 +257,10 @@ void print_hex_dump(const char *level, const char *prefix_str, int prefix_type,
>  				   linebuf, sizeof(linebuf), ascii);
>  
>  		switch (prefix_type) {
> +		case DUMP_PREFIX_UNHASHED:
> +			printk("%s%s%px: %s\n",
> +			       level, prefix_str, ptr + i, linebuf);
> +			break;
>  		case DUMP_PREFIX_ADDRESS:
>  			printk("%s%s%p: %s\n",
>  			       level, prefix_str, ptr + i, linebuf);
> -- 
> 2.25.1