linux-kernel - Re: [PATCH v11 RESEND 9/9] arm64: armv8_deprecated: apply FEAT

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aXDn3iRXEtgaUtnp@e129823.arm.com>
Date: Wed, 21 Jan 2026 14:51:10 +0000
From: Yeoreum Yun <yeoreum.yun@....com>
To: Will Deacon <will@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>, Marc Zyngier <maz@...nel.org>,
	catalin.marinas@....com, broonie@...nel.org, oliver.upton@...ux.dev,
	miko.lenczewski@....com, kevin.brodsky@....com, ardb@...nel.org,
	suzuki.poulose@....com, lpieralisi@...nel.org,
	yangyicong@...ilicon.com, scott@...amperecomputing.com,
	joey.gouly@....com, yuzenghui@...wei.com, pbonzini@...hat.com,
	shuah@...nel.org, arnd@...db.de,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kvmarm@...ts.linux.dev, kvm@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v11 RESEND 9/9] arm64: armv8_deprecated: apply FEAT_LSUI
 for swpX emulation.

> On Tue, Jan 20, 2026 at 05:59:47PM +0000, Yeoreum Yun wrote:
> > On second thought, while a CPU that implements LSUI is unlikely to
> > support AArch32 compatibility,
> > I don't think LSUI requires the absence of AArch32.
> > These two are independent features (and in fact our FVP reports/supports both).
>
> Did you have to configure the FVP specially for this or that a "default"
> configuration?
>
> > Given that, I'm not sure a WARN is really necessary.
> > Would it be sufficient to just drop the patch for swpX instead?
>
> Given that the whole point of LSUI is to remove the PAN toggling, I think
> we should make an effort to make sure that we don't retain PAN toggling
> paths at runtime that could potentially be targetted by attackers. If we
> drop the SWP emulation patch and then see that we have AArch32 at runtime,
> we should forcefully disable the SWP emulation but, since we don't actually
> think we're going to see this in practice, the WARN seemed simpler.

TBH, I missed the FVP configuration option clusterX.max_32bit_el, which
can disable AArch32 support by setting it to -1 (default: 3).
Given this, I think it’s reasonable to emit a WARN when LSUI is enabled and
drop the SWP emulation path under that condition.

Thanks!

--
Sincerely,
Yeoreum Yun