linux-kernel - Re: [RFC/RFT PATCH 2/5] memblock: introduce generic memblock_setup

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Message-ID: <YLivq1QRcStvpsLr@kernel.org>
Date:   Thu, 3 Jun 2021 13:32:11 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Mike Rapoport <rppt@...ux.ibm.com>, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        linux-mm@...ck.org, linux-s390@...r.kernel.org
Subject: Re: [RFC/RFT PATCH 2/5] memblock: introduce generic
 memblock_setup_resources()

On Wed, Jun 02, 2021 at 09:15:02PM +0100, Russell King (Oracle) wrote:
> On Wed, Jun 02, 2021 at 09:43:32PM +0300, Mike Rapoport wrote:
> > Back then when __ex_table was moved from .data section, _sdata and _edata
> > were part of the .data section. Today they are not. So something like the
> > patch below will ensure for instance that __ex_table would be a part of
> > "Kernel data" in /proc/iomem without moving it to the .data section:
> > 
> This example has undesirable security implications. It moves the
> exception table out of the read-only mappings into the read-write
> mappings, thereby providing a way for an attacker to bypass the
> read-only protection on the kernel and manipulate code pointers at
> potentially known addresses for distro built kernels.

My point was that __ex_table can be in "Kernel data" or "Kernel rodata"
without loosing the ability to sort it.
 
> You seem to be missing the point I've tried to make. The areas in
> memblock that are marked "reserved" are the areas of reserved memory
> from the firmware _plus_ the areas that the kernel has made during
> boot which are of no consequence to userspace.

I know what areas are marked "reserved" in memblock. 
I never suggested to report "ficticious" reserved areas in /proc/iomem
unless an architecture already reports them there, like arm64 for example.

You are right I should have described better the overall objective, but
sill I feel that we keep missing each other points.

I'll update the descriptions for the next repost, hopefully it'll help.

-- 
Sincerely yours,
Mike.