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Date: Wed, 21 Aug 2024 19:18:06 +0100
From: Catalin Marinas <catalin.marinas@arm.com>
To: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>, Jonathan Corbet <corbet@lwn.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Marc Zyngier <maz@kernel.org>,
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	Suzuki K Poulose <suzuki.poulose@arm.com>,
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	Eric Biederman <ebiederm@xmission.com>,
	Shuah Khan <shuah@kernel.org>,
	"Rick P. Edgecombe" <rick.p.edgecombe@intel.com>,
	Deepak Gupta <debug@rivosinc.com>, Ard Biesheuvel <ardb@kernel.org>,
	Szabolcs Nagy <Szabolcs.Nagy@arm.com>, Kees Cook <kees@kernel.org>,
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Subject: Re: [PATCH v10 23/40] arm64/signal: Set up and restore the GCS
 context for signal handlers
Message-ID: <ZsYvXqYEMYvIar28@arm.com>
References: <20240801-arm64-gcs-v10-0-699e2bd2190b@kernel.org>
 <20240801-arm64-gcs-v10-23-699e2bd2190b@kernel.org>
 <ZsYj0YYMuX1YRBZT@arm.com>
 <d5473c27-167f-46c3-9368-487ed4b657cf@sirena.org.uk>
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In-Reply-To: <d5473c27-167f-46c3-9368-487ed4b657cf@sirena.org.uk>

On Wed, Aug 21, 2024 at 07:03:13PM +0100, Mark Brown wrote:
> On Wed, Aug 21, 2024 at 06:28:49PM +0100, Catalin Marinas wrote:
> > On Thu, Aug 01, 2024 at 01:06:50PM +0100, Mark Brown wrote:
> > > +	/*
> > > +	 * Push a cap and the GCS entry for the trampoline onto the GCS.
> > > +	 */
> > > +	put_user_gcs((unsigned long)sigtramp, gcspr_el0 - 2, &ret);
> > > +	put_user_gcs(GCS_SIGNAL_CAP(gcspr_el0 - 1), gcspr_el0 - 1, &ret);
> > > +	if (ret != 0)
> > > +		return ret;
> 
> > Doesn't the second put_user_gcs() override the previous ret?
> 
> No, we only set ret on error - if the first one faults it'll set ret
> then the second one will either leave it unchanged or write the same
> error code depending on if it fails.  This idiom is used quite a lot in
> the signal code.

You are right, I missed that it's called 'err' in put_user_gcs(),
thought it's overridden.

-- 
Catalin