From: Topi Miettinen <toiwoton@gmail.com>
To: linux-hardening@vger.kernel.org, akpm@linux-foundation.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc: Jann Horn <jannh@google.com>, Kees Cook <keescook@chromium.org>,
Matthew Wilcox <willy@infradead.org>,
Mike Rapoport <rppt@kernel.org>,
Linux API <linux-api@vger.kernel.org>
Subject: Re: [PATCH v9] mm: Optional full ASLR for mmap(), mremap(), vdso, stack and heap
Date: Wed, 13 Jan 2021 13:24:04 +0200 [thread overview]
Message-ID: <ee152267-744d-b619-4400-35e3ddbac16a@gmail.com> (raw)
In-Reply-To: <20210104155316.16259-1-toiwoton@gmail.com>
On 4.1.2021 17.53, Topi Miettinen wrote:
> Writing a new value of 3 to /proc/sys/kernel/randomize_va_space
> enables full randomization of memory mappings. With 2, the base of the
> VMA used for such mappings is random, but the mappings are created in
> predictable places within the VMA and in sequential order. With 3, new
> VMAs are created to fully randomize the mappings.
>
> Mappings created with mmap(NULL, ...) are randomized and mremap(...,
> MREMAP_MAYMOVE) will move the mappings even if not necessary. The
> locations of heap (memory allocated with brk()), stack and vdso are
> also randomized.
It seems that always moving the mappings in mremap() can expose bugs
where the callers don't actually expect the mappings to move, even
though MREMAP_MAYMOVE is specified (Debian libapt-pkg6.0):
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=980037
Perhaps this part should be a separate option to avoid tripping such
bugs when compatibility is more important than improved ASLR and
debugging. The option could be also used without randomize_va_space==3.
How about something like sysctl.kernel.mremap_always_move,
sysctl.vm.mremap_always_move or CONFIG_MREMAP_ALWAYS_MOVE?
-Topi
prev parent reply other threads:[~2021-01-13 11:25 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-04 15:53 [PATCH v9] mm: Optional full ASLR for mmap(), mremap(), vdso, stack and heap Topi Miettinen
2021-01-04 20:04 ` kernel test robot
2021-01-13 11:24 ` Topi Miettinen [this message]
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