Re: [gentoo-user] Re: old kernels are installed during the upgrade

[Walter Dnes]

On Thu, Jan 04, 2018 at 11:10:01AM -0500, Rich Freeman wrote
> On Thu, Jan 4, 2018 at 11:02 AM, Holger Hoffstätte
> <holger@××××××××××××××××××.com> wrote:
> > On Wed, 03 Jan 2018 15:53:07 -0500, Rich Freeman wrote:
> >
> >> On Wed, Jan 3, 2018 at 3:35 PM, Wols Lists <antlists@××××××××××××.uk> wrote:
> >>>
> >>> And as I understand it the code can be disabled with either a compile
> >>> time option or command line switch to the kernel.
> >>
> >> I suspect the compile-time option is PAGE_TABLE_ISOLATION (which was
> >> newly added in 4.14.11).  The command line option nopti will disable
> >> it at runtime.
> >>
> >> Rumor has it that it will be disabled on AMD CPUs in 4.14.12, but I
> >
> > That's not a rumor and it can be easily verified either here:
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/stable/stable-queue.git/tree/queue-4.14/x86-cpu-x86-pti-do-not-enable-pti-on-amd-processors.patch
> >
> > or in mainline git, respectively.
> >
>
> Not back when I made my post, as is evident from the timestamps.
>
> All the info around these vulnerabilities is rapidly evolving, so take
> anything you hear with some skepticism until the dust settles...

  There are 2 vulnerabities at play here, both caused by speculative
execution...

1) "Meltdown" is the reading, by userland processes, of kernel memory.
This includes stuff like passwords, ssh and gpg keys, and other similar
sensitive stuff.  Intel is vulnerable; AMD is not, thanks to AMD's
ring-level permission checking.

2) "Spectre" is the reading, by one userland process, of memory
belonging to another userland process.  Since this does not require
jumping to kernel privilege level, AMD's ring-level permission checking
is not invoked, and AMD cpus are vulnerable.  Think "cross-site-scripting
on steroids", or "cross-process memory access" on your PC. 

  The most obvious attack vector would be web assembler or java plugin
or javascript, executing a 3rd-party ad in your browser.  By the way,
Adobe Flash is scripted by "Ecmascript", a variant of javascript.

  This is a problem that's associated with "speculative execution".  I
wonder how much of a performance hit it would be to turn off speculative
execution.  That would probably require at least a microcode/firmware
update, if not a new cpu.

-- 
Walter Dnes <waltdnes@××××××××.org>
I don't run "desktop environments"; I run useful applications