linux-kernel - Re: [PATCH v3] scripts: leaking_addresses: add support for 32-bit kernel addresses

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Date:   Thu, 7 Dec 2017 16:24:06 +1100
From:   "Tobin C. Harding" <me@...in.cc>
To:     kaiwan.billimoria@...il.com
Cc:     Alexander Kapshuk <alexander.kapshuk@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v3] scripts: leaking_addresses: add support for 32-bit
 kernel addresses

On Thu, Dec 07, 2017 at 09:41:58AM +0530, kaiwan.billimoria@...il.com wrote:
> On Thu, 2017-12-07 at 10:01 +1100, Tobin C. Harding wrote:
> > On Wed, Dec 06, 2017 at 05:21:30PM +0530, kaiwan.billimoria@...il.com wrote:
> > > On Wed, 2017-12-06 at 15:04 +1100, Tobin C. Harding wrote:
> > > > 
> > > Sure, lets try for a generic ver!
> > 
> > Cool.
> > 
> > > Thanks for your help on this..
> > 
> > No problem.
> > 
> > > As your experience woth the R Pi shows, we may have to just resort to building a
> > > generic framework of sorts, letting folks "plugin" appropriate "truth values"
> > > for their particular platform; this way, we support as much as we can for now
> > > and, going forward, it's generic.
> > > As of right now though, am unsure what this "generic framework" is..
> > 
> > ATM the best I can come up with is having two flags
> > 
> > --page-offset-32bit=0xc0000000 (exactly as we have now)
> > --32-bit
> > 
> > Now for the klunky bit, I can only see two options
> > 
> > 1. Default to 64 bit, for 32 bit scan require one of the above options
> > to be set.
> 
> Yes, agreed..
> > 
> > 2. Parse config file for all architectures, if CONFIG_PAGE_OFFSET is set
> > us it.
> > 
> > I particularly don't like option 2. If we can find a reliable way to get
> > the architecture the we have a better option. At the moment the method
> > we use relies on the architecture of the machine that the Perl binary
> > was built on (AFAICT).
> > 
> > (/usr/bin/arch does not work on RPi either)
> 
> Right, reg arch: nor on some of the Yocto platforms I tested.
> > 
> > I'm happy with option 1 unless there is a better proposal.
> > thanks,
> > Tobin.
> 
> Okay, I can start working on the approach above. So, that implies that the
> is_supported_architecture sub (and it's descendants) are now redundant, correct?

We still need it for differentiating between 64 bit architectures. So
far it appears to work (x86_64 and ppc64).

> Also, I think we can perhaps still make use of the 'uname -m' to advantage:
> 
> 1. A scenario: the user runs the script with no options; we default to 64-bit.
> But, the platform is actually 32-bit. So, we run a sanity check regardless - if
> we find that the platform is indeed 32-bit but the user has not run with the
> --32-bit (or --page-offset-32bit) option switch(es), we could:
>    - (a) emit a noisy Warning message to stderr and continue, ("batch mode"), OR

Yeah, I see no problem with this.

>    - (b) fail, with the error message and a failure code.
> 
> Of course if we go with (a), the results will be meaningless; so, just failing might be better.
> Again, I realize that all this will only work if detection of 32-bit actually works!
> I'll take a stab at this..
> 
> 2. Modify the show_detected_architecture sub to use it (for 'debug' case).

Yep, I say keep it for debugging.

thanks,
Tobin.