Re: [PATCH] arm64/vdso: Discard .note.gnu.property sections in vDSO

From: Bill Wendling <morbo@google.com>
To: Mark Brown <broonie@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Kees Cook <keescook@google.com>, Ard Biesheuvel <ardb@kernel.org>,
	Will Deacon <will@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	Szabolcs Nagy <szabolcs.nagy@arm.com>,
	Daniel Kiss <Daniel.Kiss@arm.com>
Subject: Re: [PATCH] arm64/vdso: Discard .note.gnu.property sections in vDSO
Date: Wed, 28 Apr 2021 12:21:38 -0700	[thread overview]
Message-ID: <CAGG=3QUATefn9AG+HvnCfEOBv3iRu4fzFwfmA7Djrh2CmP_weA@mail.gmail.com> (raw)
In-Reply-To: <20210428174010.GA4593@sirena.org.uk>

On Wed, Apr 28, 2021 at 10:40 AM Mark Brown <broonie@kernel.org> wrote:
> On Wed, Apr 28, 2021 at 06:28:47PM +0100, Catalin Marinas wrote:
> > On Fri, Apr 23, 2021 at 01:51:59PM -0700, Bill Wendling wrote:
>
> > > Since the note.gnu.property section in the vDSO is not checked by the
> > > dynamic linker, discard the .note.gnu.property sections in the vDSO.
>
> > Can we not instead fix the linker script to preserve the
> > .note.gnu.property, correctly aligned? It doesn't take much space and
> > while we don't use it now, it has the BTI information about the binary.
>
> > Cc'ing a few others who were involved in the BTI support.
>
> Not just BTI, we also flag PAC usage in there too and could add other
> extensions going forwards.  While the note isn't actively used by
> anything right now due to the kernel mapping the vDSO prior to userspace
> starting it is part of the ABI and something could end up wanting to use
> it and getting confused if it's not there.  It would be much better to
> fix the alignment issue.

If there's only one of the 8-byte aligned sections guaranteed, we
could place it first in the note. Otherwise, we will have to change
the alignment of the note (or somehow merge multiple notes).

-bw