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Date: Wed, 7 Mar 2018 15:18:16 +0200
From: Igor Stoppa <igor.stoppa@...wei.com>
To: J Freyensee <why2jjj.linux@...il.com>, <david@...morbit.com>,
<willy@...radead.org>, <keescook@...omium.org>, <mhocko@...nel.org>
CC: <labbott@...hat.com>, <linux-security-module@...r.kernel.org>,
<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
<kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH 6/7] lkdtm: crash on overwriting protected pmalloc var
On 06/03/18 19:20, J Freyensee wrote:
> On 2/28/18 12:06 PM, Igor Stoppa wrote:
[...]
>> void __init lkdtm_perms_init(void);
>> void lkdtm_WRITE_RO(void);
>> void lkdtm_WRITE_RO_AFTER_INIT(void);
>> +void lkdtm_WRITE_RO_PMALLOC(void);
>
> Does this need some sort of #ifdef too?
Not strictly. It's just a function declaration.
As long as it is not used, the linker will not complain.
The #ifdef placed around the use and definition is sufficient, from a
correctness perspective.
But it's a different question if there is any standard in linux about
hiding also the declaration.
I am not very fond of #ifdefs, so when I can I try to avoid them.
>> + pr_info("attempting bad pmalloc write at %p\n", i);
>> + *i = 0;
>
> OK, now I'm on the right version of this patch series, same comment
> applies. I don't get the local *i assignment at the end of the
> function, but seems harmless.
Because that's the whole point of the function: prove that pmalloc
protection works (see the message in the pr_info one line above).
The function is supposed to do:
* create a pool
* allocate memory from it
* protect it
* try to alter it (and crash)
*i = 0; performs the last step
--
igor
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