linux-hardening - Re: [PATCH v5 00/32] ARM vmap'ed and IRQ stacks roundup

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Date:   Mon, 24 Jan 2022 18:57:52 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-hardening@...r.kernel.org, Nicolas Pitre <nico@...xnic.net>,
        Arnd Bergmann <arnd@...db.de>,
        Kees Cook <keescook@...omium.org>,
        Keith Packard <keithpac@...zon.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tony Lindgren <tony@...mide.com>,
        Marc Zyngier <maz@...nel.org>,
        Vladimir Murzin <vladimir.murzin@....com>,
        Jesse Taube <mr.bossman075@...il.com>
Subject: Re: [PATCH v5 00/32] ARM vmap'ed and IRQ stacks roundup

On Mon, 24 Jan 2022 at 18:57, Russell King (Oracle)
<linux@...linux.org.uk> wrote:
>
> On Mon, Jan 24, 2022 at 06:47:12PM +0100, Ard Biesheuvel wrote:
> > This v5 series is a combined followup to
> >
> > - IRQ stacks support for v7 SMP systems [0],
> > - vmap'ed stacks support for v7 SMP systems[1],
> > - extending support for both IRQ stacks and vmap'ed stacks for all
> >   remaining configurations, including v6/v7 SMP multiplatform kernels
> >   and uniprocessor configurations including v7-M [2]
> >
> > [0] https://lore.kernel.org/linux-arm-kernel/20211115084732.3704393-1-ardb@kernel.org/
> > [1] https://lore.kernel.org/linux-arm-kernel/20211122092816.2865873-1-ardb@kernel.org/
> > [2] https://lore.kernel.org/linux-arm-kernel/20211206164659.1495084-1-ardb@kernel.org/
> >
> > This work was queued up in the ARM tree for a while, but due to problems
> > with the vmap'ed stacks code, which was difficult to revert in
> > isolation, the whole stack was dropped again.
> >
> > In order to prevent similar problems from occurring this time around,
> > the series was reorganized so that the vmap'ed stacks changes appear at
> > the very end, which also results in a more natural progression of the
> > changes.
> >
> > Changes since v4:
> > - incorporate fixups to avoid build failures on Clang related to
> >   literals in subsections,
> > - switch from the ID map to swapper_pg_dir as early as possible when
> >   onlining a CPU on !LPAE, to ensure that the stack is mapped,
> > - use SMP_ON_UP patching to elide HWCAP_TLS tests on SMP+v6,
> > - clean up __switch_to() for Thumb2 a bit more,
> > - add patch to make the vmalloc_seq counter SMP safe,
> > - use enter_lazy_tlb() hook on !LPAE to ensure that the active_mm used
> >   by a kernel thread has a mapping for its vmap'ed stack,
>
> Hi Ard,
>
> I still have the original code in devel-stable, and being a guaranteed
> stable branch, it's not something I'll be dropping... Please can I have
> fixes on top of what is already there please?
>

Sure.