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Message-ID: <ZmmUAUl_zuXnA_0O@optiplex-fbsd>
Date: Wed, 12 Jun 2024 08:26:41 -0400
From: Rafael Aquini <aquini@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
Heiko Carstens <hca@...ux.ibm.com>, Petr Mladek <pmladek@...e.com>,
Mike Rapoport <rppt@...nel.org>, Paul McKenney <paulmck@...nel.org>,
Samuel Holland <samuel.holland@...ive.com>
Subject: Re: [PATCH v2] mm: mmap: allow for the maximum number of bits for
randomizing mmap_base by default
On Tue, Jun 11, 2024 at 07:43:12PM -0700, Andrew Morton wrote:
> On Tue, 11 Jun 2024 21:35:24 -0400 Rafael Aquini <aquini@...hat.com> wrote:
>
> > > Shouldn't we make this the default (at least for 32-bit) so the
> > > regressed kernels are fixed simply by applying this patch?
> > >
> >
> > That is a fair take, indeed. I guess we could do something like
> >
> > config FORCE_MAX_MMAP_RND_BITS
> > bool "Force maximum number of bits to use for ASLR of mmap base address"
> > - default n
> > + default y if !64BIT
>
> "something like" != "exhaustively tested" ;)
>
> I'll toss that in there, but please do let me know when it is suitable
> for an upstream merge.
>
The follow-up patch does work as intended:
[raquini@...iplex-lnx linux]$ make ARCH=i386 defconfig
*** Default configuration is based on 'i386_defconfig'
#
# configuration written to .config
#
[raquini@...iplex-lnx linux]$ grep MMAP_RND_BITS .config
CONFIG_ARCH_MMAP_RND_BITS_MIN=8
CONFIG_ARCH_MMAP_RND_BITS_MAX=16
CONFIG_HAVE_ARCH_MMAP_RND_BITS=y
# CONFIG_FORCE_MAX_MMAP_RND_BITS is not set
CONFIG_ARCH_MMAP_RND_BITS=8
[raquini@...iplex-lnx linux]$ patch -Np1 < patch.diff
patching file arch/Kconfig
[raquini@...iplex-lnx linux]$ make ARCH=i386 defconfig
*** Default configuration is based on 'i386_defconfig'
#
# configuration written to .config
#
[raquini@...iplex-lnx linux]$ grep MMAP_RND_BITS .config
CONFIG_ARCH_MMAP_RND_BITS_MIN=8
CONFIG_ARCH_MMAP_RND_BITS_MAX=16
CONFIG_HAVE_ARCH_MMAP_RND_BITS=y
CONFIG_FORCE_MAX_MMAP_RND_BITS=y
CONFIG_ARCH_MMAP_RND_BITS=16
> I also added cc:stable.
>
Thank you, Andrew.
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