linux-kernel - Re: [PATCH v4 2/3] fdt: add support for rng-seed

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Message-ID: <CANMq1KA1YF6B=nFizS8nT4KREASaJuaztdBnh_t0V8i0Fb-e6A@mail.gmail.com>
Date:   Tue, 21 May 2019 20:42:48 +0800
From:   Nicolas Boichat <drinkcat@...omium.org>
To:     Hsin-Yi Wang <hsinyi@...omium.org>
Cc:     linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        lkml <linux-kernel@...r.kernel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Miles Chen <miles.chen@...iatek.com>,
        James Morse <james.morse@....com>,
        Andrew Murray <andrew.murray@....com>,
        Mark Rutland <mark.rutland@....com>,
        Jun Yao <yaojun8558363@...il.com>, Yu Zhao <yuzhao@...gle.com>,
        Robin Murphy <robin.murphy@....com>,
        Laura Abbott <labbott@...hat.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v4 2/3] fdt: add support for rng-seed

On Tue, May 21, 2019 at 12:10 PM Hsin-Yi Wang <hsinyi@...omium.org> wrote:
>
> On Mon, May 20, 2019 at 7:54 AM Nicolas Boichat <drinkcat@...omium.org> wrote:
>
> > Alphabetical order.
> Original headers are not sorted, should I sort them here?
> >
>
> >
> > I'm a little bit concerned about this, as we really want the rng-seed
> > value to be wiped, and not kept in memory (even if it's hard to
> > access).
> >
> > IIUC, fdt_delprop splices the device tree, so it'll override
> > "rng-seed" property with whatever device tree entries follow it.
> > However, if rng-seed is the last property (or if the entries that
> > follow are smaller than rng-seed), the seed will stay in memory (or
> > part of it).
> >
> > fdt_nop_property in v2 would erase it for sure. I don't know if there
> > is a way to make sure that rng-seed is removed for good while still
> > deleting the property (maybe modify fdt_splice_ to do a memset(.., 0)
> > of the moved chunk?).
> >
> So maybe we can use fdt_nop_property() back?

Yes I prefer fdt_nop_property, if we don't want to modify delprop or
splice. But it'd be good if others can chime in.