linux-kernel - Re: [PATCH] arm64: defconfig: update and enable CONFIG_RANDOMIZE

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Date:   Tue, 25 Jun 2019 17:42:49 +0200
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Will Deacon <will@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Kees Cook <keescook@...gle.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Jeffrey Vander Stoep <jeffv@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Arnd Bergmann <arnd@...db.de>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Will Deacon <will.deacon@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        Jagan Teki <jagan@...rulasolutions.com>,
        Olof Johansson <olof@...om.net>,
        Shawn Guo <shawnguo@...nel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm64: defconfig: update and enable CONFIG_RANDOMIZE_BASE

On Tue, 25 Jun 2019 at 17:39, Catalin Marinas <catalin.marinas@....com> wrote:
>
> On Mon, Jun 24, 2019 at 12:06:18PM +0200, Ard Biesheuvel wrote:
> > On Mon, 24 Jun 2019 at 11:57, Will Deacon <will@...nel.org> wrote:
> > > Thanks for having a look. It could be that we've fixed the issue Catalin was
> > > running into in the past -- he was going to see if the problem persists with
> > > mainline, since it was frequent enough that it was causing us to ignore the
> > > results from our testing infrastructure when RANDOMIZE_BASE=y.
> >
> > I had no idea this was the case. I can look into it if we are still
> > seeing failures.
>
> I've seen the panic below with 5.2-rc1, defconfig + RANDOMIZE_BASE=y in
> a guest on TX2. It takes a few tries to trigger just with kaslr,
> enabling lots of other DEBUG_* options makes the failures more
> deterministic. I can't really say it's kaslr's fault here, only that I
> used to consistently get it in this configuration. For some reason, I
> can no longer reproduce it on arm64 for-next/core (or maybe it just
> takes more tries and my script doesn't catch this).
>
> The fault is in the ip_tables module, the __this_cpu_read in
> xt_write_recseq_begin() inlined in ipt_do_table(). The disassembled
> sequence in my build:
>
> 0000000000000188 <ipt_do_table>:
> ...
>      258:       d538d080        mrs     x0, tpidr_el1
>      25c:       aa1303f9        mov     x25, x19
>      260:       b8606b34        ldr     w20, [x25, x0]
>

This was fixed recently by

arm64/kernel: kaslr: reduce module randomization range to 2 GB

(and arm64/module: deal with ambiguity in PRELxx relocation ranges to
some extent)