CachePC
=======

This repository contains proof-of-concept code for a novel cache side-channel
attack dubbed PRIME+COUNT that we demonstrate can be used to circumvent
AMD's latest secure virtualization solution SEV-SNP to access sensitive
guest information.

Several test-cases were used to verify parts of the exploit chain separately:

test/eviction:
	Demonstrate that performance counters & our setup are accurate enough
	to detect a single eviction in L1 cache and infer its cache set
	through PRIME+COUNT

test/kvm-eviction:
	Demonstrate that the cache set of a memory access instruction can be
	inferred in non-SEV / SEV / SEV-ES / SEV-SNP -enabled vms respectively.

test/kvm-step:
	Demonstrate that SEV-SNP enabled vms can be single-stepped using local
	APIC timers to interrupt the guest and increment the interrupt interval
	while observing the RIP+RFLAGS ciphertext in the VMSA for changes to
	detect that a single instruction has been executed.

test/kvm-pagestep:
	Demonstrate that a SEV-SNP enabled vm can be quickly single-stepped
	and analyzed by tracking a single page at a time. This type
	of tracking creates a page-wise profile of the guests execution,
	which can be used to infer what the guest is doing and to begin
	fine-grained single-stepping.

test/qemu-eviction:
	Replicate result from kvm-eviction on a qemu-based vm running debian
	using a specially crafted guest program to signal when measurement
	should take place to infer the accessed set.

test/qemu-aes:
	Demonstrate that AES encryption keys can be leaked from a
	modified qemu-based linux guest.

test/qemu-poc:
	Demonstrate that AES encryption keys can be leaked from an
	unmodified qemu-based linux guest.

Testing was done on a bare-metal AMD EPYC 72F3 (Family 0x19, Model 0x01)
cpu and Supermicro H12SSL-i V1.01 motherboard. The following BIOS settings
differ from the defaults:

Advanced > CPU Configuration > Local APIC Mode = xAPIC
Advanced > CPU Configuration > L1 Stream HW Prefetcher = Disabled
Advanced > CPU Configuration > L2 Stream HW Prefetcher = Disabled
Advanced > CPU Configuration > SMEE = Enabled
Advanced > CPU Configuration > SEV ASID Count = 509
Advanced > CPU Configuration > SEV ASID Space Limit Control = Manual
Advanced > CPU Configuration > SEV ASID Space Limit = 110
Advanced > CPU Configuration > SNP Memory (RMP Table) Coverage = Enabled
Advanced > North Bridge Configuration > SEV-SNP Support = Enabled
Advanced > North Bridge Configuration > Memory Configuration > TSME = Disabled
Advanced > PCI Devices Common Settings > Memory Configuration > TSME = Disabled

To successfully build and load the kvm.ko and kvm-amd.ko modules, ensure
that a host kernel debian package was built using `make host`.

Note: because of bad decisions made in regards to version control,
the checked out commit of the modified kernel (previously the
kernel patch file) might be incorrect for older revisions.