All of lore.kernel.org
 help / color / mirror / Atom feed
From: Alexandre ghiti <alex@ghiti.fr>
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Michael Ellerman <mpe@ellerman.id.au>
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	linux-mm@kvack.org
Subject: Re: [PATCH 6/8] mm: Allow arch specific arch_randomize_brk() with CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
Date: Mon, 22 Nov 2021 13:57:56 +0100	[thread overview]
Message-ID: <eb070ba0-2131-cc4e-4742-ec20c13d72ef@ghiti.fr> (raw)
In-Reply-To: <2dd4a22e-f1a5-683c-2d17-ce726f03f4c5@csgroup.eu>

On 11/22/21 12:47, Christophe Leroy wrote:
>
>
> Le 22/11/2021 à 12:22, Alex Ghiti a écrit :
>> Hi Christophe,
>>
>> Le 22/11/2021 à 09:48, Christophe Leroy a écrit :
>>> Commit e7142bf5d231 ("arm64, mm: make randomization selected by
>>> generic topdown mmap layout") introduced a default version of
>>> arch_randomize_brk() provided when
>>> CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT is selected.
>>>
>>> powerpc could select CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
>>> but needs to provide its own arch_randomize_brk().
>>>
>>> In order to allow that, don't make
>>> CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT select
>>> CONFIG_ARCH_HAS_ELF_RANDOMIZE. Instead, ensure that
>>> selecting CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT and
>>> selecting CONFIG_ARCH_HAS_ELF_RANDOMIZE has the same effect.
>>
>> This feels weird to me since if CONFIG_ARCH_HAS_ELF_RANDOMIZE is used 
>> somewhere else at some point, it is not natural to add 
>> CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT: can't we use a __weak 
>> function or a new CONFIG_ARCH_HAS_RANDOMIZE_BRK?
>
>
> Yes I also found things a bit weird.
>
> CONFIG_ARCH_HAS_RANDOMIZE_BRK could be an idea but how different would 
> it be from CONFIG_ARCH_HAS_ELF_RANDOMIZE ? In fact I find it weird 
> that CONFIG_ARCH_HAS_ELF_RANDOMIZE is selected by 
> CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT and not by the arch itself.


IIRC, this was a request from Kees Cook who wanted to enforce this 
security measure.


>
> On the other hand CONFIG_ARCH_HAS_ELF_RANDOMIZE also handles 
> arch_mmap_rnd() and here we are talking about arch_randomize_brk() only.
>
> In the begining I was thinking about adding a 
> CONFIG_ARCH_WANT_DEFAULT_RANDOMIZE_BRK, but it was meaning adding it 
> to the few other arches selecting 
> CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT.
>
> So I think I will go for the __weak function option.


Ok, thanks.

Alex


>
> Thanks
> Christophe

WARNING: multiple messages have this Message-ID (diff)
From: Alexandre ghiti <alex@ghiti.fr>
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Michael Ellerman <mpe@ellerman.id.au>
Cc: linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 6/8] mm: Allow arch specific arch_randomize_brk() with CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
Date: Mon, 22 Nov 2021 13:57:56 +0100	[thread overview]
Message-ID: <eb070ba0-2131-cc4e-4742-ec20c13d72ef@ghiti.fr> (raw)
In-Reply-To: <2dd4a22e-f1a5-683c-2d17-ce726f03f4c5@csgroup.eu>

On 11/22/21 12:47, Christophe Leroy wrote:
>
>
> Le 22/11/2021 à 12:22, Alex Ghiti a écrit :
>> Hi Christophe,
>>
>> Le 22/11/2021 à 09:48, Christophe Leroy a écrit :
>>> Commit e7142bf5d231 ("arm64, mm: make randomization selected by
>>> generic topdown mmap layout") introduced a default version of
>>> arch_randomize_brk() provided when
>>> CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT is selected.
>>>
>>> powerpc could select CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
>>> but needs to provide its own arch_randomize_brk().
>>>
>>> In order to allow that, don't make
>>> CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT select
>>> CONFIG_ARCH_HAS_ELF_RANDOMIZE. Instead, ensure that
>>> selecting CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT and
>>> selecting CONFIG_ARCH_HAS_ELF_RANDOMIZE has the same effect.
>>
>> This feels weird to me since if CONFIG_ARCH_HAS_ELF_RANDOMIZE is used 
>> somewhere else at some point, it is not natural to add 
>> CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT: can't we use a __weak 
>> function or a new CONFIG_ARCH_HAS_RANDOMIZE_BRK?
>
>
> Yes I also found things a bit weird.
>
> CONFIG_ARCH_HAS_RANDOMIZE_BRK could be an idea but how different would 
> it be from CONFIG_ARCH_HAS_ELF_RANDOMIZE ? In fact I find it weird 
> that CONFIG_ARCH_HAS_ELF_RANDOMIZE is selected by 
> CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT and not by the arch itself.


IIRC, this was a request from Kees Cook who wanted to enforce this 
security measure.


>
> On the other hand CONFIG_ARCH_HAS_ELF_RANDOMIZE also handles 
> arch_mmap_rnd() and here we are talking about arch_randomize_brk() only.
>
> In the begining I was thinking about adding a 
> CONFIG_ARCH_WANT_DEFAULT_RANDOMIZE_BRK, but it was meaning adding it 
> to the few other arches selecting 
> CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT.
>
> So I think I will go for the __weak function option.


Ok, thanks.

Alex


>
> Thanks
> Christophe

  reply	other threads:[~2021-11-22 12:58 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-22  8:48 [PATCH 0/8] Convert powerpc to default topdown mmap layout Christophe Leroy
2021-11-22  8:48 ` Christophe Leroy
2021-11-22  8:48 ` [PATCH 1/8] powerpc/mm: Make slice specific to book3s/64 Christophe Leroy
2021-11-22  8:48   ` Christophe Leroy
2021-11-22 14:48   ` kernel test robot
2021-11-22 14:48     ` kernel test robot
2021-11-22 14:48     ` kernel test robot
2021-11-24 12:10     ` Christophe Leroy
2021-11-24 12:10       ` Christophe Leroy
2021-11-24 12:10       ` Christophe Leroy
2021-11-24 13:49       ` Christophe Leroy
2021-11-24 13:49         ` Christophe Leroy
2021-11-26  5:15         ` [kbuild-all] " Chen, Rong A
2021-11-26  5:15           ` Chen, Rong A
2021-11-22 21:10   ` kernel test robot
2021-11-22 21:10     ` kernel test robot
2021-11-22 21:10     ` kernel test robot
2021-11-24 12:10     ` Christophe Leroy
2021-11-24 12:10       ` Christophe Leroy
2021-11-24 12:10       ` Christophe Leroy
2021-11-22  8:48 ` [PATCH 2/8] powerpc/mm: Remove CONFIG_PPC_MM_SLICES Christophe Leroy
2021-11-22  8:48   ` Christophe Leroy
2021-11-22  8:48 ` [PATCH 3/8] powerpc/mm: Remove asm/slice.h Christophe Leroy
2021-11-22  8:48   ` Christophe Leroy
2021-11-22  8:48 ` [PATCH 4/8] powerpc/mm: Move vma_mmu_pagesize() and hugetlb_get_unmapped_area() to slice.c Christophe Leroy
2021-11-22  8:48   ` Christophe Leroy
2021-11-22  8:48 ` [PATCH 5/8] powerpc/mm: Call radix__arch_get_unmapped_area() from arch_get_unmapped_area() Christophe Leroy
2021-11-22  8:48   ` Christophe Leroy
2021-11-22  8:48 ` [PATCH 6/8] mm: Allow arch specific arch_randomize_brk() with CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT Christophe Leroy
2021-11-22  8:48   ` Christophe Leroy
2021-11-22 11:22   ` Alex Ghiti
2021-11-22 11:22     ` Alex Ghiti
2021-11-22 11:47     ` Christophe Leroy
2021-11-22 11:47       ` Christophe Leroy
2021-11-22 12:57       ` Alexandre ghiti [this message]
2021-11-22 12:57         ` Alexandre ghiti
2021-11-23  0:22   ` kernel test robot
2021-11-23  0:22     ` kernel test robot
2021-11-23  0:22     ` kernel test robot
2021-11-22  8:48 ` [PATCH 7/8] powerpc/mm: Convert to default topdown mmap layout Christophe Leroy
2021-11-22  8:48   ` Christophe Leroy
2021-11-22  8:48 ` [PATCH 8/8] powerpc/mm: Properly randomise mmap with slices Christophe Leroy
2021-11-22  8:48   ` Christophe Leroy
2021-11-24 13:21 ` [PATCH 0/8] Convert powerpc to default topdown mmap layout Nicholas Piggin
2021-11-24 13:21   ` Nicholas Piggin
2021-11-24 13:40   ` Christophe Leroy
2021-11-24 13:40     ` Christophe Leroy
2021-11-24 18:00     ` Christophe Leroy

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=eb070ba0-2131-cc4e-4742-ec20c13d72ef@ghiti.fr \
    --to=alex@ghiti.fr \
    --cc=benh@kernel.crashing.org \
    --cc=christophe.leroy@csgroup.eu \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=linuxppc-dev@lists.ozlabs.org \
    --cc=mpe@ellerman.id.au \
    --cc=paulus@samba.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.