linux-kernel - Re: [PATCH v6 3/7] arm64: uaccess: Add additional userspace GCS accessors

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Message-ID: <7bc27e3d-7667-4366-89bc-93a084808ace@sirena.org.uk>
Date: Wed, 20 Aug 2025 18:24:24 +0100
From: Mark Brown <broonie@...nel.org>
To: Jeremy Linton <jeremy.linton@....com>
Cc: linux-trace-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
	mhiramat@...nel.org, oleg@...hat.com, peterz@...radead.org,
	mingo@...hat.com, acme@...nel.org, namhyung@...nel.org,
	mark.rutland@....com, alexander.shishkin@...ux.intel.com,
	jolsa@...nel.org, irogers@...gle.com, adrian.hunter@...el.com,
	kan.liang@...ux.intel.com, thiago.bauermann@...aro.org,
	yury.khrustalev@....com, kristina.martsenko@....com,
	liaochang1@...wei.com, catalin.marinas@....com, will@...nel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 3/7] arm64: uaccess: Add additional userspace GCS
 accessors

On Mon, Aug 18, 2025 at 04:34:48PM -0500, Jeremy Linton wrote:

> Its important to note that GCS pages can be read by normal
> instructions, but the hardware validates that pages used by GCS
> specific operations, have a GCS privilege set. We aren't validating this
> in load_user_gcs because it requires stabilizing the VMA over the read
> which may fault.

I think in the context of uprobes this is reasonable.  We can always go
back later and tighten things up.

Reviewed-by: Mark Brown <broonie@...nel.org>

> +/*
> + * Unlike put/push_user_gcs() above, get/pop_user_gsc() doesn't
> + * validate the GCS permission is set on the page being read.  This
> + * differs from how the hardware works when it consumes data stored at
> + * GCSPR. Callers should assure this is acceptable.

s/assure/ensure/

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