linux-kernel - Re: [PATCH] arm64/sme: Move storage of reg_smidr to __cpuinfo_store

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: <Z2Agntn52mY5bSTp@J2N7QTR9R3>
Date: Mon, 16 Dec 2024 12:44:14 +0000
From: Mark Rutland <mark.rutland@....com>
To: Mark Brown <broonie@...nel.org>
Cc: Marc Zyngier <maz@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Peter Collingbourne <pcc@...gle.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] arm64/sme: Move storage of reg_smidr to
 __cpuinfo_store_cpu()

On Mon, Dec 16, 2024 at 12:17:54PM +0000, Mark Brown wrote:
> On Sat, Dec 14, 2024 at 10:56:13AM +0000, Marc Zyngier wrote:
> 
> > I don't understand the need to single out SMIDR_EL1. It seems to only
> > make things even more fragile than they already are by adding more
> > synchronisation phases.
> 
> > Why isn't the following a good enough fix? It makes it plain that
> > boot_cpu_data is only a copy of CPU0's initial boot state.
> 
> That would work but it's not clear to me that that is what the intent is
> here.  The current ordering seemed like a strange enough decision to be
> deliberate, though I couldn't identify the reasoning.

The original intent was that __cpuinfo_store_cpu() read *all* of a CPU's
implemented ID regs, and init_cpu_features() initialised the expected
system features based on the boot CPU's ID regs.

The expectation was that init_cpu_features() would only consume the
register values, and would not alter the cpuinfo_arm64 values, so the
order of:

	boot_cpu_data = *info;
	init_cpu_features(&boot_cpu_data);

... didn't matter either way, and using '&boot_cpu_data' was intended to
make it clear that the features were based on the boot CPU's info, even
if you just grepped for that and didn't see the surrounding context.

I think the real fix here is to move the reading back into
__cpuinfo_store_cpu(), but to have an explicit check that SME has been
disabled on the commandline, with a comment explaining that this is a
bodge for broken FW which traps the SME ID regs.

Mark.