linux-kernel - Re: [PATCH v10 18/40] arm64/mm: Handle GCS data aborts

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Message-ID: <24d33455-d958-4f27-8a2c-4f237fc2bd29@sirena.org.uk>
Date: Mon, 19 Aug 2024 16:14:41 +0100
From: Mark Brown <broonie@...nel.org>
To: Catalin Marinas <catalin.marinas@....com>
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,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v10 18/40] arm64/mm: Handle GCS data aborts

On Mon, Aug 19, 2024 at 10:17:52AM +0100, Catalin Marinas wrote:
> On Thu, Aug 01, 2024 at 01:06:45PM +0100, Mark Brown wrote:

> > +static bool is_invalid_gcs_access(struct vm_area_struct *vma, u64 esr)
> > +{

> > +	if (unlikely(is_gcs_fault(esr))) {
> > +		/* GCS accesses must be performed on a GCS page */
> > +		if (!(vma->vm_flags & VM_SHADOW_STACK))
> > +			return true;
> > +		if (!(vma->vm_flags & VM_WRITE))
> > +			return true;

> Do we need the VM_WRITE check here? Further down in do_page_fault(), we
> already do the check as we set vm_flags = VM_WRITE.

> >       if (!(vma->vm_flags & vm_flags)) {
> >               vma_end_read(vma);
> >               fault = 0;

It looks bitrotted, yes.

> I was wondering whether we should prevent mprotect(PROT_READ) on the GCS
> page. But I guess that's fine, we'll SIGSEGV later if we get an invalid
> GCS access.

Yeah, that doesn't seem like a particular problem - the concern is
adding rather than removing GCS.

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