linux-kernel - Re: [kernel-hardening] Re: [PATCH v4] scripts: add leaking

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Message-ID: <CAPDLWs9vqBYJs+OUHyfs_tKVY1RUS5JMtp4N6LjgHn5z0pgaqA@mail.gmail.com>
Date:   Mon, 13 Nov 2017 10:57:16 +0530
From:   Kaiwan N Billimoria <kaiwan@...wantech.com>
To:     "Tobin C. Harding" <me@...in.cc>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        kernel-hardening@...ts.openwall.com,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        "Theodore Ts'o" <tytso@....edu>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Tycho Andersen <tycho@...ker.com>,
        "Roberts, William C" <william.c.roberts@...el.com>,
        Tejun Heo <tj@...nel.org>,
        Jordan Glover <Golden_Miller83@...tonmail.ch>,
        Greg KH <gregkh@...uxfoundation.org>,
        Petr Mladek <pmladek@...e.com>, Joe Perches <joe@...ches.com>,
        Ian Campbell <ijc@...lion.org.uk>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <wilal.deacon@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Chris Fries <cfries@...gle.com>,
        Dave Weinstein <olorin@...gle.com>,
        Daniel Micay <danielmicay@...il.com>,
        Djalal Harouni <tixxdz@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>
Subject: Re: [kernel-hardening] Re: [PATCH v4] scripts: add leaking_addresses.pl

On Mon, Nov 13, 2017 at 10:05 AM, Tobin C. Harding <me@...in.cc> wrote:
> On Mon, Nov 13, 2017 at 06:37:28AM +0300, Kirill A. Shutemov wrote:
>> On Mon, Nov 13, 2017 at 10:06:46AM +1100, Tobin C. Harding wrote:
>> > On Sun, Nov 12, 2017 at 02:10:07AM +0300, Kirill A. Shutemov wrote:
...
>> >
>> > Thanks for the link. So it looks like we need to refactor the kernel
>> > address regular expression into a function that takes into account the
>> > machine architecture and the number of page table levels. We will need
>> > to add this to the false positive checks also.
>> >
>> > > Not sure if we care. It won't work too for other 64-bit architectrues that
>> > > have more than 256TB of virtual address space.
>> >
>> > Is this because of the virtual memory map?
>>
>> On x86 direct mapping is the nearest thing we have to userspace.
>>
>> > Did you mean 512TB?
>>
>> No, I mean 256TB.
>>
>> You have all kernel memory in the range from 0xffff000000000000 to
>> 0xffffffffffffffff if you have 256 TB of virtual address space. If you
>> hvae more, some thing might be ouside the range.
>
> Doesn't 4-level paging already limit a system to 64TB of memory? So any
> system better equipped than this will use 5-level paging right? If I am
> totally talking rubbish please ignore, I'm appreciative that you pointed
> out the limitation already. Perhaps we can add a comment to the script
>
> # Script may miss some addresses on machines with more than 256TB of
> # memory.

I think the 256TB is wrt *virtual* address space not physical RAM.

Also, IMHO, the script should 'transparently' take into account the # of paging
levels (instead of the user needing to pass a parameter).
IOW it should be able to detect the same (say, from the .config file) and act
accordingly - in the sense, the regex's and associated logic would accordingly
differ.