From: Kees Cook <kees@kernel.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Yuntao Liu <liuyuntao12@huawei.com>,
x86@kernel.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org,
linux-hardening@vger.kernel.org, catalin.marinas@arm.com,
will@kernel.org, hca@linux.ibm.com, gor@linux.ibm.com,
agordeev@linux.ibm.com, borntraeger@linux.ibm.com,
svens@linux.ibm.com, tglx@linutronix.de, mingo@redhat.com,
bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com,
gustavoars@kernel.org, arnd@arndb.de, leobras@redhat.com,
broonie@kernel.org, imbrenda@linux.ibm.com,
pawan.kumar.gupta@linux.intel.com
Subject: Re: [PATCH] remove AND operation in choose_random_kstack_offset()
Date: Mon, 17 Jun 2024 11:22:55 -0700 [thread overview]
Message-ID: <202406171122.B5FDA6A@keescook> (raw)
In-Reply-To: <ZnBbr2CAqBGDe2aN@J2N7QTR9R3>
On Mon, Jun 17, 2024 at 04:52:15PM +0100, Mark Rutland wrote:
> On Mon, Jun 17, 2024 at 01:37:21PM +0000, Yuntao Liu wrote:
> > Since the offset would be bitwise ANDed with 0x3FF in
> > add_random_kstack_offset(), so just remove AND operation here.
> >
> > Signed-off-by: Yuntao Liu <liuyuntao12@huawei.com>
>
> The comments in arm64 and x86 say that they're deliberately capping the
> offset at fewer bits than the result of KSTACK_OFFSET_MAX() masking the
> value with 0x3FF.
>
> Maybe it's ok to expand that, but if that's the case the commit message
> needs to explain why it's safe add extra bits (2 on arm64, 3 on s39 and
> x86), and those comments need to be updated accordingly.
>
> As-is, I do not think this patch is ok.
Yeah, I agree: the truncation is intentional and tuned to the
architecture.
--
Kees Cook
next prev parent reply other threads:[~2024-06-17 18:23 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-06-17 13:37 [PATCH] remove AND operation in choose_random_kstack_offset() Yuntao Liu
2024-06-17 15:52 ` Mark Rutland
2024-06-17 18:22 ` Kees Cook [this message]
2024-06-17 20:33 ` Arnd Bergmann
2024-06-17 23:31 ` Kees Cook
2024-06-18 6:46 ` Arnd Bergmann
2024-06-18 10:45 ` Mark Rutland
2024-06-18 11:14 ` Arnd Bergmann
2024-06-18 11:51 ` Mark Rutland
2024-06-20 4:04 ` liuyuntao (F)
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