linux-hardening - Re: [REBASE PATCH v5 08/17] arm64: mm: Add dynamic ramoops region support through command line

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Message-ID: <202309131613.C0E12D0D14@keescook>
Date:   Wed, 13 Sep 2023 16:17:29 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Will Deacon <will@...nel.org>
Cc:     Mukesh Ojha <quic_mojha@...cinc.com>, corbet@....net,
        agross@...nel.org, andersson@...nel.org, konrad.dybcio@...aro.org,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        conor+dt@...nel.org, tony.luck@...el.com, gpiccoli@...lia.com,
        mathieu.poirier@...aro.org, catalin.marinas@....com,
        linus.walleij@...aro.org, andy.shevchenko@...il.com,
        vigneshr@...com, nm@...com, matthias.bgg@...il.com,
        kgene@...nel.org, alim.akhtar@...sung.com, bmasney@...hat.com,
        quic_tsoni@...cinc.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-hardening@...r.kernel.org, linux-remoteproc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-gpio@...r.kernel.org,
        linux-mediatek@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, kernel@...cinc.com
Subject: Re: [REBASE PATCH v5 08/17] arm64: mm: Add dynamic ramoops region
 support through command line

On Tue, Sep 12, 2023 at 11:18:20AM +0100, Will Deacon wrote:
> On Mon, Sep 11, 2023 at 04:23:50PM +0530, Mukesh Ojha wrote:
> > The reserved memory region for ramoops is assumed to be at a fixed
> > and known location when read from the devicetree. This may not be
> > required for something like Qualcomm's minidump which is interested
> > in knowing addresses of ramoops region but it does not put hard
> > requirement of address being fixed as most of it's SoC does not
> > support warm reset and does not use pstorefs at all instead it has
> > firmware way of collecting ramoops region if it gets to know the
> > address and register it with apss minidump table which is sitting
> > in shared memory region in DDR and firmware will have access to
> > these table during reset and collects it on crash of SoC.
> > 
> > So, add the support of reserving ramoops region to be dynamically
> > allocated early during boot if it is request through command line
> > via 'dyn_ramoops_size=' and fill up reserved resource structure and
> > export the structure, so that it can be read by ramoops driver.
> > 
> > Signed-off-by: Mukesh Ojha <quic_mojha@...cinc.com>
> > ---
> >  arch/arm64/mm/init.c       | 94 ++++++++++++++++++++++++++++++++++++++++++++++
> 
> Why does this need to be in the arch code? There's absolutely nothing
> arm64-specific here.

I would agree: this needs to be in ramoops itself, IMO. It should be a
ramoops module argument, too.

It being unhelpful for systems that don't have an external consumer is
certainly true, but I think it would still make more sense for this
change to live entirely within ramoops. Specifically: you're
implementing a pstore backend behavioral change. In the same way that
patch 10 is putting the "output" side of this into pstore/, I'd expect
the "input" side also in pstore/

More comments there, though.

-- 
Kees Cook