linux-kernel - Re: [PATCH v7 36/39] selftests/arm64: Add GCS signal tests

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Date: Thu, 18 Jan 2024 21:10:43 +0000
From: Mark Brown <broonie@...nel.org>
To: Thiago Jung Bauermann <thiago.bauermann@...aro.org>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Jonathan Corbet <corbet@....net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marc Zyngier <maz@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	James Morse <james.morse@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Arnd Bergmann <arnd@...db.de>, Oleg Nesterov <oleg@...hat.com>,
	Eric Biederman <ebiederm@...ssion.com>,
	Kees Cook <keescook@...omium.org>, Shuah Khan <shuah@...nel.org>,
	"Rick P. Edgecombe" <rick.p.edgecombe@...el.com>,
	Deepak Gupta <debug@...osinc.com>, Ard Biesheuvel <ardb@...nel.org>,
	Szabolcs Nagy <Szabolcs.Nagy@....com>,
	"H.J. Lu" <hjl.tools@...il.com>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Florian Weimer <fweimer@...hat.com>,
	Christian Brauner <brauner@...nel.org>,
	linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
	kvmarm@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
	linux-arch@...r.kernel.org, linux-mm@...ck.org,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v7 36/39] selftests/arm64: Add GCS signal tests

On Sat, Dec 16, 2023 at 11:12:37PM -0300, Thiago Jung Bauermann wrote:
> Mark Brown <broonie@...nel.org> writes:

> > +/* This should be includable from some standard header, but which? */
> > +#ifndef SEGV_CPERR
> > +#define SEGV_CPERR 10
> > +#endif

> One suggestion is include/uapi/asm-generic/siginfo.h. It already has
> SEGV_MTEAERR and SEGV_MTESERR, as well as si_codes specific to other
> arches.

Sadly the testsuite is being very clever with redefining siginfo_t which
means it conflicts with that header.  I'll update the comment.

> > +	if (!get_current_context(td, &context.uc, sizeof(context))) {
> > +		fprintf(stderr, "Failed getting context\n");
> > +		return 1;
> > +	}

> At this point, before any function call is made, can the test check that
> *(gcspr + 8) == 0? This would detect the issue I mentioned in
> patch 24 of gcs_restore_signal() not zeroing the location of the cap.

Sure.

> > +	if (gcs->gcspr != gcspr) {
> > +		fprintf(stderr, "Got GCSPR %llx but expected %lx\n",
> > +			gcs->gcspr, gcspr);
> > +		return 1;
> > +	}

> I suggest adding a new check here to ensure that gcs->reserved == 0.

This would mean that you couldn't use an old kselftest build to verify
a new kernel that starts using the reserved bits.  It's niche but it
does seem like something that should work.

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