Subject: Re: [PATCH v4] scripts: add leaking_addresses.pl

From: "Tobin C. Harding" <[email-masked]>
Date: Mon, 13 Nov 2017 10:06:46 +1100

On Sun, Nov 12, 2017 at 02:10:07AM +0300, Kirill A. Shutemov wrote:
> On Tue, Nov 07, 2017 at 09:32:11PM +1100, Tobin C. Harding wrote:
> > Currently we are leaking addresses from the kernel to user space. This
> > script is an attempt to find some of those leakages. Script parses
> > `dmesg` output and /proc and /sys files for hex strings that look like
> > kernel addresses.
> > 
> > Only works for 64 bit kernels, the reason being that kernel addresses
> > on 64 bit kernels have 'ffff' as the leading bit pattern making greping
> > possible. On 32 kernels we don't have this luxury.
> 
> Well, it's not going to work as well as intented on x86 machine with
> 5-level paging. Kernel address space there starts at 0xff10000000000000.
> It will still catch pointers to kernel/modules text, but the rest is
> outside of 0xffff... space. See Documentation/x86/x86_64/mm.txt.

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? Did you mean 512TB?

from mm.txt:
ffd4000000000000 - ffd5ffffffffffff (=49 bits) virtual memory map (512TB)

Perhaps an option (--terse) that only checks the virtual memory map
range (above for 5-level paging) and

ffffea0000000000 - ffffeaffffffffff (=40 bits) virtual memory map (1TB)

for 4-level paging?

> Just wanted to point to the limitation.

Appreciate it, thanks.

Tobin.