On Mon, Jun 25, 2018 at 11:39 PM, ron minnich <rminnich(a)gmail.com> wrote:
> On Mon, Jun 25, 2018 at 12:55 AM Shawn <citypw(a)gmail.com> wrote:
>> Hi Ron,
>> IIRC, Machine mode in RISC-V is just looking similar to SMM in x86.
>> But it can do more than what SMM does.
> that's in my view not good, since in many cases, M mode code is part of
> firmware, not the kernel image. Kernels don't get to change or ignore it. M
> mode can protect itself from the kernel, even from being read. So it can
> hide its presence, what it does, and might even be able to change itself.
> I had a talk with a BIG ARM SOC vendor not long ago. They said that at one
> point a big x86 company proposed that their company implement SMM for ARM.
> "so they asked us to implement this SMM-like thing that had unlimited
> privilege. We said no, no no, there's no reason to repeat x86 mistakes on
> ARM". Good call on that company's part.
> I argued several years ago that M mode code should be supplied by the
> kernel, not firmware, for the obvious reasons: M mode is a great place to
> put a persistent threat. The various x86 experiences were well known by that
> time, so the problem should have been pretty clear.
Well, from that perspective I'm totally agree w/ SMM is a big threat
especially when the machine was compromised and then attacker implant
a rootkit running in SMM. If that happened in x86, it's pretty much
fuc*ed up. Cu'z it's unlikely detect the smm rootkit at runtime, while
the static analysis of forensics cost more time/money. Maybe we
should've taken mitigation( SMRAM?) into this case in the 1st place.
GNU powered it...
GPL protect it...
God blessing it...