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

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Date:   Sat, 16 Jan 2021 14:54:52 -0600
From:   Timur Tabi <timur@...nel.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Roman Fietze <roman.fietze@...na.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] lib/hexdump: introduce DUMP_PREFIX_UNHASHED for unhashed addresses

On Fri, Jan 15, 2021 at 3:24 AM Petr Mladek <pmladek@...e.com> wrote:

> By other words, every print_hex_dump() used need to be reviewed in
> which context might be called.

I did a rough analysis of all current usage of DUMP_PREFIX_ADDRESS in
the kernel, compared to the introduction of %px and hashed addresses,
using git-blame to find the most recent commit that modifies a line
that contains _ADDRESS.  Of 150 cases, 110 of them are newer than %px,
so I'm assuming that these developers chose _ADDRESS instead of
_OFFSET knowing that the addresses are hashed.

> > If you want, I can include a patch that changes a few callers of
> > print_hex_dump() to use DUMP_PREFIX_UNHASHED, based on what I think would be
> > useful.
>
> It would be nice.

I have a v2 that I'm about to post, and I included a patch that
modifies check_poison_mem() in mm/page_poison.c.  I chose this file
because I figured actual addresses would probably be necessary for
tracking memory-related errors.  Also, that call to print_hex_dump()
was added back in 2009, so it predates the introduction of %px.