linux-kernel - Re: [PATCH 1/2] x86: Increase brk randomness entropy on x86

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Message-ID: <nycvar.YFH.7.76.2402261138370.21798@cbobk.fhfr.pm>
Date: Mon, 26 Feb 2024 11:39:35 +0100 (CET)
From: Jiri Kosina <jikos@...nel.org>
To: Kees Cook <keescook@...omium.org>
cc: y0un9n132@...il.com, Geert Uytterhoeven <geert@...ux-m68k.org>, 
    Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
    Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, 
    "H. Peter Anvin" <hpa@...or.com>, Peter Zijlstra <peterz@...radead.org>, 
    Qi Zheng <zhengqi.arch@...edance.com>, 
    Alexandre Ghiti <alexghiti@...osinc.com>, x86@...nel.org, 
    Al Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, 
    Jan Kara <jack@...e.cz>, Eric Biederman <ebiederm@...ssion.com>, 
    Christophe Leroy <christophe.leroy@...roup.eu>, 
    Josh Poimboeuf <jpoimboe@...nel.org>, 
    "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, 
    Rick Edgecombe <rick.p.edgecombe@...el.com>, 
    Brian Gerst <brgerst@...il.com>, Bjorn Helgaas <bhelgaas@...gle.com>, 
    Tony Battersby <tonyb@...ernetics.com>, linux-kernel@...r.kernel.org, 
    linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, 
    linux-hardening@...r.kernel.org
Subject: Re: [PATCH 1/2] x86: Increase brk randomness entropy on x86_64

On Fri, 16 Feb 2024, Kees Cook wrote:

> In commit c1d171a00294 ("x86: randomize brk"), arch_randomize_brk() was
> defined to use a 32MB range (13 bits of entropy), but was never increased
> when moving to 64-bit. The default arch_randomize_brk() uses 32MB for
> 32-bit tasks, and 1GB (18 bits of entropy) for 64-bit tasks. Update
> x86_64 to match the entropy used by arm64 and other 64-bit architectures.
> 
> Reported-by: y0un9n132@...il.com
> Closes: https://lore.kernel.org/linux-hardening/CA+2EKTVLvc8hDZc+2Yhwmus=dzOUG5E4gV7ayCbu0MPJTZzWkw@mail.gmail.com/
> Signed-off-by: Kees Cook <keescook@...omium.org>

Wow, this is a pretty aged code indeed.

	Acked-by: Jiri Kosina <jkosina@...e.com>

Thanks,

-- 
Jiri Kosina
SUSE Labs