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

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

On Wed, Apr 28, 2021 at 10:40 AM Mark Brown <broonie@...nel.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