linux-kernel - Re: [PATCH v5 4/7] arm64: probes: Add GCS support to bl/blr/ret

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Message-ID: <aJ8_aH7ncFfznl8S@arm.com>
Date: Fri, 15 Aug 2025 15:08:40 +0100
From: Catalin Marinas <catalin.marinas@....com>
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,
	broonie@...nel.org, yury.khrustalev@....com,
	kristina.martsenko@....com, liaochang1@...wei.com, will@...nel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 4/7] arm64: probes: Add GCS support to bl/blr/ret

On Mon, Aug 11, 2025 at 09:10:07AM -0500, Jeremy Linton wrote:
> The arm64 probe simulation doesn't currently have logic in place
> to deal with GCS and this results in core dumps if probes are inserted
> at control flow locations. Fix-up bl, blr and ret to manipulate the
> shadow stack as needed.
> 
> While we manipulate and validate the shadow stack correctly, the
> hardware provides additional security by only allowing GCS operations
> against pages which are marked to support GCS. For writing there is
> gcssttr() which enforces this, but there isn't an equivalent for
> reading. This means that uprobe users should be aware that probing on
> control flow instructions which require reading the shadow stack (ex:
> ret) offers lower security guarantees than what is achieved without
> the uprobe active.
> 
> Signed-off-by: Jeremy Linton <jeremy.linton@....com>

Reviewed-by: Catalin Marinas <catalin.marinas@....com>