From: Kees Cook <kees@kernel.org>
To: Ryan Roberts <ryan.roberts@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>,
linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
Andrew Morton <akpm@linux-foundation.org>,
Ali Saidi <alisaidi@amazon.com>,
linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] binfmt_elf: Move brk for static PIE even if ASLR disabled
Date: Thu, 1 May 2025 16:49:11 -0700 [thread overview]
Message-ID: <202505011633.82A962A7@keescook> (raw)
In-Reply-To: <a6696d0f-3c5a-46a8-8d38-321292dac83d@arm.com>
On Thu, May 01, 2025 at 12:03:32PM +0100, Ryan Roberts wrote:
> I agree, as long as COMPAT_BRK is not set (which is the common case IFAICT).
> When COMPAT_BRK is enabled, I think you are breaking the purpose of that
> Kconfig? Perhaps it's not a real-world problem though...
When you turned off ASLR, what mechanism did you use? Personality or
randomize_va_space=0?
> > It's possible it could break running the loader directly against some
> > libc5-based binaries. If this turns out to be a real-world issue, we can
> > find a better solution (perhaps pre-allocating a large brk).
>
> But how large is large enough...
Right -- Chrome has a 500MB brk on my laptop. :P Or with randomization
off, it could allocate to the top of the mmap space just to keep
"future" mmap allocations from landing in any holes...
> Perhaps it is safer to only move the brk if !IS_ENABLED(CONFIG_COMPAT_BRK) ?
> Then wait to see if there are any real-world COMPAT_BRK users that hit the issue?
Yeah, that might be the best middle-ground.
--
Kees Cook
next prev parent reply other threads:[~2025-05-01 23:49 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-04-25 22:45 Kees Cook
2025-04-28 10:14 ` Ryan Roberts
2025-04-30 19:53 ` Kees Cook
2025-05-01 11:03 ` Ryan Roberts
2025-05-01 23:49 ` Kees Cook [this message]
2025-05-02 10:34 ` Ryan Roberts
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