I most likely don't understand how this is supposed to work but aren't we here successfully reading SMRAM from non-SMM context, something we are not supposed to be able to do?
We are aren't reading SMRAM at 0x30000 base directly, "RAM" marked log lines are non-SMM context reads using as base BUILD_SMM_INIT_ADDR 0x30000 and as you see, it isn't showing anything from SMRAM
For mgmt/demo purposes SMRAM (which is at 0x30000 in SMM address space) is also aliased at BUILD_SMM_ADDR 0xa0000 into non-SMM address space to allow us to initialize SMM entry point (log entries are marked as "SMRAM").
OK, I then misunderstood the purpose of this demo. I thought you were not supposed to be able to read it from either location in non-SMM mode.
Thanks for the explanation.
-boris
Aliased SMRAM also allows us to check that relocation worked (i.e. smm_base was relocated from default "handle_smi cmd=0 smbase=0x00030000" to a new one "smm_relocate: SMRAM cpu.i64.smm_base a0000").
It's similar to what we do with TSEG where QEMU steals RAM from normal address space and puts MMIO region 'tseg_blackhole' over it so non-SMM context reads 0xFF from TSEG window, while SMM context accesses RAM hidden below tseg_blackhole.
These patches show that we can have normal usable RAM at 0x30000 which doesn't overlap with SMRAM at the same address and each can be made accessible only from its own mode (no-SMM and SMM). Preventing non-SMM mode from injecting attack on SMRAM via CPU that hasn't been initialized yet once firmware locked down SMRAM.
