linux-kernel - Re: [PATCH v10 13/40] arm64/mm: Map pages for guarded control stack

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Message-ID: <ZsTSnx_IEqF-RkyJ@arm.com>
Date: Tue, 20 Aug 2024 18:30:07 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Mark Brown <broonie@...nel.org>
Cc: 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>,
	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>, Kees Cook <kees@...nel.org>,
	"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>,
	Thiago Jung Bauermann <thiago.bauermann@...aro.org>,
	Ross Burton <ross.burton@....com>,
	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,
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	linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v10 13/40] arm64/mm: Map pages for guarded control stack

On Tue, Aug 20, 2024 at 04:28:21PM +0100, Mark Brown wrote:
> On Tue, Aug 20, 2024 at 03:59:21PM +0100, Catalin Marinas wrote:
> > On Mon, Aug 19, 2024 at 05:33:24PM +0100, Mark Brown wrote:
> > > On Mon, Aug 19, 2024 at 10:10:36AM +0100, Catalin Marinas wrote:
> > > > Is there any arch restriction with setting BTI and GCS? It doesn't make
> > > > sense but curious if it matters. We block the exec permission anyway
> > > > (unless the BTI pages moved to PIE as well, I don't remember).
> 
> > > As you say BTI should be meaningless for a non-executable page like GCS,
> > > I'm not aware of any way in which it matters.  BTI is separate to PIE.
> 
> > My thoughts were whether we can get rid of this hunk entirely by
> > handling it in the core code. We'd allow BTI if one wants such useless
> > combination but clear VM_MAYEXEC in the core code (and ignore VM_SHARED
> > since you can't set it anyway).
> 
> I have to admit that the BTI because I was shoving _EXEC in there rather
> than because it specifically needed to be blocked.  So change the check
> for VM_SHARED to a VM_WARN_ON(), and leave the _EXEC check for now
> pending the above core change?

Yes, sounds good.

-- 
Catalin