From: Kees Cook <kees@kernel.org>
To: Iurii Trukhin <yuri@trukhin.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Anshuman Khandual <anshuman.khandual@arm.com>,
Ryan Roberts <ryan.roberts@arm.com>,
Ard Biesheuvel <ardb@kernel.org>,
"Gustavo A. R. Silva" <gustavoars@kernel.org>,
linux-arm-kernel@lists.infradead.org,
linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] arm64: raise default ARCH_MMAP_RND_BITS for 48-bit and 52-bit VA
Date: Wed, 14 Oct 2026 18:10:43 -0700 [thread overview]
Message-ID: <202610141810.779BBFF@keescook> (raw)
In-Reply-To: <CAOx7e9Jm0N9O_ndL1UApMPrXUN=P4RiptSNibdDP+9prUsNPOw@mail.gmail.com>
On Wed, Oct 14, 2026 at 07:26:48PM -0500, Iurii Trukhin wrote:
> Since commit f101c5644771 ("arm64: Support ARM64_VA_BITS=52 when
> setting ARCH_MMAP_RND_BITS_MAX"), arm64 supports up to 33, 31, and 29
> bits of mmap ASLR entropy on 48-bit and 52-bit virtual address spaces
> for 4K, 16K, and 64K pages respectively. However, ARCH_MMAP_RND_BITS
> still defaults to ARCH_MMAP_RND_BITS_MIN (18, 16, and 14 bits), which
> was set in commit 8f0d3aa9de57 ("arm64: mm: support ARCH_MMAP_RND_BITS")
> when 39-bit VA was the 4K default.
>
> Set the default ARCH_MMAP_RND_BITS for 48-bit and 52-bit VA to 28 (4K
> pages), 26 (16K pages), and 24 (64K pages), matching x86_64's 1 TiB
> randomization range (5 bits below ARCH_MMAP_RND_BITS_MAX) while keeping
> ARCH_MMAP_RND_BITS_MIN unchanged for smaller VA configurations.
>
> Closes: https://github.com/KSPP/linux/issues/371
> Signed-off-by: Iurii Trukhin <yuri@trukhin.com>
Yes please. :)
Reviewed-by: Kees Cook <kees@kernel.org>
--
Kees Cook
next prev parent reply other threads:[~2026-10-15 1:11 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-15 0:26 [PATCH] arm64: raise default ARCH_MMAP_RND_BITS for 48-bit and 52-bit VA Iurii Trukhin
2026-10-15 1:10 ` Kees Cook [this message]
2026-10-15 4:55 ` Anshuman Khandual
2026-10-15 5:22 ` Iurii Trukhin
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