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Date:   Tue, 29 Oct 2019 04:05:16 -0700 (PDT)
From:   Christian Kujau <lists@nerdbynature.de>
To:     Kees Cook <keescook@chromium.org>
cc:     Andrew Morton <akpm@linux-foundation.org>,
        zhanglin <zhang.lin16@zte.com.cn>, dan.j.williams@intel.com,
        jgg@ziepe.ca, mingo@kernel.org, dave.hansen@linux.intel.com,
        namit@vmware.com, bp@suse.de, christophe.leroy@c-s.fr,
        rdunlap@infradead.org, osalvador@suse.de,
        richardw.yang@linux.intel.com, linux-kernel@vger.kernel.org,
        xue.zhihong@zte.com.cn, wang.yi59@zte.com.cn,
        jiang.xuexin@zte.com.cn
Subject: Re: [PATCH] kernel: Restrict permissions of /proc/iomem.
In-Reply-To: <201910281213.720C0DB89@keescook>
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On Mon, 28 Oct 2019, Kees Cook wrote:
> > It's risky to change things like this - heaven knows which userspace
> > applications might break.
> > 
> > Possibly we could obfuscate the information if that is considered
> > desirable.  Why is this a problem anyway?  What are the possible
> > exploit scenarios?
> 
> This is already done: kptr_restrict sysctl already zeros these values
> if it is set. e.g.:
> 
> 00000000-00000000 : System RAM
>   00000000-00000000 : Kernel code
>   00000000-00000000 : Kernel data
>   00000000-00000000 : Kernel bss
> 
> > Can't the same info be obtained by running dmesg and looking at the
> > startup info?
> 
> Both virtual and physical address dumps in dmesg are considered "bad
> form" these days and most have been removed.
> 
> > Can't the user who is concerned about this run chmod 0400 /proc/iomem
> > at boot?
> 
> That is also possible.

As a user, I still like this patch, or some variation of it. On various 
(server and desktop) systems I do this during boot for some time now and 
never had a problem:

find /proc -xdev -mindepth 1 -maxdepth 1 ! \( -name "[0-9]*" \
  -o -name cpuinfo -o -name modules -o -name loadavg -o -name meminfo \ 
  -o -name mounts -o -name net -o -name self -o -name diskstats \
  -o -name stat -o -name sys -o -name swaps -o -name thread-self \
  -o -name vmstat -o -name uptime \) -exec chmod -c go-rwx '{}' +

C.
-- 
BOFH excuse #436:

Daemon escaped from pentagram