Re: [PATCH v2] arm64: Introduce prctl(PR_PAC_{SET,GET}_ENABLED_KEYS)

From: Florian Weimer <fw@deneb.enyo.de>
To: Dave Martin <Dave.Martin@arm.com>
Cc: Peter Collingbourne <pcc@google.com>,
	libc-alpha@sourceware.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	Kevin Brodsky <kevin.brodsky@arm.com>,
	linux-api@vger.kernel.org, Kostya Serebryany <kcc@google.com>,
	Evgenii Stepanov <eugenis@google.com>,
	Andrey Konovalov <andreyknvl@google.com>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Will Deacon <will@kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2] arm64: Introduce prctl(PR_PAC_{SET,GET}_ENABLED_KEYS)
Date: Wed, 18 Nov 2020 18:31:21 +0100	[thread overview]
Message-ID: <874klmvafq.fsf@mid.deneb.enyo.de> (raw)
In-Reply-To: <20201118171945.GG6882@arm.com> (Dave Martin's message of "Wed, 18 Nov 2020 17:19:45 +0000")

* Dave Martin:

> IIUC the default compiler options when using PAC will only use the
> A key, and only use the PAC instructions that execute as NOPs when the
> affected key is disabled (precisely so that the code still runs on non-
> PAC supporting hardware).  But you can't simply flip it on and off while
> there are function frames on the stack that assume it's either on or off.

I think we can do the switch at the top-most frame, at least in ld.so.
I have not thought about statically linked binaries. 8-/