linux-kernel - Re: [PATCH v11 19/39] arm64/mm: Handle GCS data aborts

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Message-ID: <Zsd1zxJ1n5-_lpbx@finisterre.sirena.org.uk>
Date: Thu, 22 Aug 2024 18:30:55 +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>,
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	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>,
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	kvmarm@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
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Subject: Re: [PATCH v11 19/39] arm64/mm: Handle GCS data aborts

On Thu, Aug 22, 2024 at 06:19:38PM +0100, Catalin Marinas wrote:
> On Thu, Aug 22, 2024 at 05:44:19PM +0100, Mark Brown wrote:
> > On Thu, Aug 22, 2024 at 05:12:30PM +0100, Catalin Marinas wrote:
> > > On Thu, Aug 22, 2024 at 02:15:22AM +0100, Mark Brown wrote:
> > 
> > > > +static bool is_invalid_gcs_access(struct vm_area_struct *vma, u64 esr)
> > 
> > > > +	} else if (unlikely(vma->vm_flags & VM_SHADOW_STACK)) {
> > > > +		/* Only GCS operations can write to a GCS page */
> > > > +		return is_write_abort(esr);
> > > > +	}

> > Yes, that should check for a data abort.  I think I'd formed the
> > impression that is_write_abort() included that check somehow.  As you
> > say it's to avoid spinning trying to resolve a permission fault for a
> > write (non-GCS reads to a GCS page are valid), I do think we need the 
> > is_write_abort() since non-GCS reads are valid so something like:
> > 
> > 	if (!esr_is_data_abort(esr))
> > 		return false;
> > 
> > 	return is_write_abort(esr);
> 
> We do need the write abort check but not unconditionally, only if to a
> GCS page (you can have other genuine write aborts).

tThat was to replace the checks in the above case, not the function as a
whole.

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