<s>
The	O
AMD	B-Device
Platform	I-Device
Security	I-Device
Processor	I-Device
(	O
PSP	B-Device
)	O
,	O
officially	O
known	O
as	O
AMD	B-Device
Secure	I-Device
Technology	I-Device
,	O
is	O
a	O
trusted	O
execution	O
environment	O
subsystem	O
incorporated	O
since	O
about	O
2013	O
into	O
AMD	O
microprocessors	O
.	O
</s>
<s>
AMD	O
has	O
denied	O
requests	O
to	O
open	O
source	O
the	O
code	O
that	O
runs	O
on	O
the	O
PSP	B-Device
.	O
</s>
<s>
The	O
PSP	B-Device
itself	O
represents	O
an	O
ARM	O
core	O
with	O
the	O
TrustZone	O
extension	O
which	O
is	O
inserted	O
into	O
the	O
main	O
CPU	O
die	O
as	O
a	O
coprocessor	B-General_Concept
.	O
</s>
<s>
The	O
PSP	B-Device
contains	O
on-chip	O
firmware	O
which	O
is	O
responsible	O
for	O
verifying	O
the	O
SPI	O
ROM	O
and	O
loading	O
off-chip	O
firmware	O
from	O
it	O
.	O
</s>
<s>
In	O
2019	O
,	O
a	O
Berlin-based	O
security	O
group	O
discovered	O
the	O
off-chip	O
firmware	O
in	O
ordinary	O
UEFI	B-Architecture
image	O
files	O
(	O
the	O
code	O
that	O
boots	O
up	O
the	O
operating	O
system	O
)	O
,	O
which	O
meant	O
that	O
it	O
could	O
be	O
easily	O
analyzed	O
.	O
</s>
<s>
By	O
using	O
a	O
few	O
hand-written	O
Python-based	O
tools	O
,	O
they	O
found	O
that	O
the	O
off-chip	O
firmware	O
from	O
the	O
SPI	O
ROM	O
contained	O
an	O
application	O
resembling	O
an	O
entire	O
micro	O
operating	O
system	O
.	O
</s>
<s>
Investigation	O
of	O
a	O
Lenovo	O
ThinkPad	O
A285	O
notebook	O
's	O
motherboard	O
flash	O
chip	O
(	O
stores	O
UEFI	B-Architecture
firmware	I-Architecture
)	O
revealed	O
that	O
the	O
PSP	B-Device
core	O
itself	O
(	O
as	O
a	O
device	O
)	O
is	O
run	O
before	O
the	O
main	O
CPU	O
and	O
that	O
its	O
firmware	O
bootstrapping	B-Application
process	O
starts	O
just	O
before	O
basic	O
UEFI	B-Architecture
gets	O
loaded	O
.	O
</s>
<s>
They	O
discovered	O
that	O
the	O
firmware	O
is	O
run	O
inside	O
in	O
the	O
same	O
system	O
's	O
memory	O
space	O
that	O
user	O
's	O
applications	O
do	O
with	O
unrestricted	O
access	O
to	O
it	O
(	O
including	O
MMIO	B-Architecture
)	O
raising	O
concerns	O
over	O
data	O
safety	O
.	O
</s>
<s>
Because	O
PSP	B-Device
is	O
the	O
chip	O
that	O
decides	O
whenever	O
the	O
x86	O
cores	O
will	O
run	O
or	O
not	O
,	O
it	O
is	O
used	O
to	O
implement	O
hardware	O
downcoring	O
,	O
specific	O
cores	O
on	O
the	O
system	O
can	O
be	O
made	O
permanently	O
inaccessible	O
during	O
manufacturing	O
.	O
</s>
<s>
The	O
PSP	B-Device
also	O
provides	O
a	O
random	O
number	O
generator	O
for	O
the	O
RDRAND	O
instruction	O
and	O
provides	O
TPM	O
services	O
.	O
</s>
<s>
The	O
PSP	B-Device
is	O
an	O
integral	O
part	O
of	O
the	O
boot	O
process	O
,	O
without	O
which	O
the	O
x86	O
cores	O
would	O
never	O
be	O
activated	O
.	O
</s>
<s>
On-chip	O
phase	O
Firmware	O
located	O
directly	O
on	O
the	O
PSP	B-Device
chip	O
sets	O
up	O
the	O
ARM	O
CPU	O
,	O
verifies	O
the	O
integrity	O
of	O
the	O
SPI	O
ROM	O
and	O
using	O
various	O
data	O
structures	O
locates	O
the	O
off-chip	O
firmware	O
and	O
copies	O
it	O
over	O
to	O
internal	O
PSP	B-Device
memory	O
.	O
</s>
<s>
Using	O
the	O
previous	O
data	O
structures	O
the	O
off-chip	O
firmware	O
finds	O
UEFI	B-Architecture
firmware	I-Architecture
within	O
the	O
SPI	O
ROM	O
and	O
copies	O
it	O
over	O
to	O
DRAM	O
,	O
it	O
may	O
perform	O
additional	O
verification	O
steps	O
and	O
if	O
the	O
system	O
is	O
deemed	O
secure	O
,	O
it	O
will	O
release	O
the	O
x86	O
cores	O
from	O
their	O
reset	O
state	O
,	O
thus	O
starting	O
UEFI	B-Architecture
firmware	I-Architecture
.	O
</s>
<s>
In	O
September	O
2017	O
,	O
Google	O
security	O
researcher	O
Cfir	O
Cohen	O
reported	O
a	O
vulnerability	O
to	O
AMD	O
of	O
a	O
PSP	B-Device
subsystem	O
that	O
could	O
allow	O
an	O
attacker	O
access	O
to	O
passwords	O
,	O
certificates	O
,	O
and	O
other	O
sensitive	O
information	O
;	O
a	O
patch	O
was	O
rumored	O
to	O
become	O
available	O
to	O
vendors	O
in	O
December	O
2017	O
.	O
</s>
<s>
In	O
March	O
2018	O
,	O
an	O
Israeli	O
IT	O
security	O
company	O
reported	O
a	O
handful	O
of	O
allegedly	O
serious	O
flaws	O
related	O
to	O
the	O
PSP	B-Device
in	O
AMD	O
's	O
Zen	O
architecture	O
CPUs	O
(	O
EPYC	O
,	O
Ryzen	O
,	O
Ryzen	O
Pro	O
,	O
and	O
Ryzen	O
Mobile	O
)	O
that	O
could	O
allow	O
malware	O
to	O
run	O
and	O
gain	O
access	O
to	O
sensitive	O
information	O
.	O
</s>
