[coreboot-gerrit] [M] Change in coreboot[main]: arch/riscv: linuxcheck framework which runs from ramstage

[ron minnich (Code Review)]

Attention is currently required from: Arthur Heymans, Maximilian Brune, Philipp Hug.

Hello Arthur Heymans, Maximilian Brune, Philipp Hug, build bot (Jenkins),

I'd like you to reexamine a change. Please visit

https://review.coreboot.org/c/coreboot/+/81367?usp=email

to look at the new patch set (#10).

The following approvals got outdated and were removed:
Verified+1 by build bot (Jenkins)

Change subject: arch/riscv: linuxcheck framework which runs from ramstage
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arch/riscv: linuxcheck framework which runs from ramstage

Errors in Linux booting are notoriously hard to debug.

This change adds a linuxcheck framework that allows testing of
things Linux (and other kernels) needs, without having to debug Linux.

If LINUXCHECK is set during menuconfig, the linuxcheck function
will be called, in S mode, from the ramstage. That function
then runs code, in S mode, that tests coreboot M mode code
such as SBI.

This is extremely handy: because linuxcheck is built
into the ramstage, it allows calling any ramstage function,
e.g. printk, if required; at the same time, the function is running
in S mode, so it is very easy to test SBI calls, instruction
emulation, and so on. Note that, if CONFIG_LINUXCHECK is set,
the PMPs should enable RWX permissions (instead of R permissions)
on the ramstage. For now, until we get the rest of the debugging
done, we unconditionally set the permissions.

This is a very powerful approach that could also form the core of
an SBI fuzzing suite; unlike the currently proposed one, which is based
on the KVM fuzzer, this code would not require a Linux kernel to test.
It is very light weight.

This is also better than the older linuxcheck payload, since it
does not need libpayload or seperate compilation. It reduces
the testing of SBI and other trap code to its simplest
form, and allows to focus on testing SBI, not fighting
build systems and large complex kernels.

Change-Id: I7d19147b9df57c63ec7301da243fd5541e9952a7
Signed-off-by: Ronald G Minnich 
---
M src/arch/riscv/Kconfig
M src/arch/riscv/Makefile.mk
M src/arch/riscv/include/arch/cpu.h
A src/arch/riscv/linuxcheck.c
M src/arch/riscv/payload.c
M src/arch/riscv/trap_handler.c
6 files changed, 129 insertions(+), 0 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/67/81367/10