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Change cpu_monitor to security_monitor and to also check RAM 

Change name of cpu_monitor to security_monitor and increase its
functionality to include RAM access violations. If addresses in RAM
but outside of physical RAM is accessed in any way the
security_monitor traps the CPU in the same way as it already did for
execution violations.
This commit is contained in:
Joachim Strömbergson 2024-03-19 13:17:14 +01:00 committed by Michael Cardell Widerkrantz
parent 3fb6d66cf3
commit 8784a24b33
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GPG Key ID: D3DB3DDF57E704E5
2 changed files with 52 additions and 33 deletions
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50
hw/application_fpga/core/tk1/README.md
View File

@ -129,7 +129,7 @@ data itself is scrambled. FW writes random values to these registers
during boot.
### Execution monitor
### Security monitor
```
ADDR_CPU_MON_CTRL: 0x60
@ -137,39 +137,41 @@ during boot.
ADDR_CPU_MON_LAST: 0x62
```
These registers control the execution monitor related to the RAM. Once
enabled, by writing to ADDR_CPU_MON_CTRL, the memory are defined by
ADDR_CPU_MON_FIRST and ADDR_CPU_MON_LAST inclusive will be protected
against execution. Typically this will be the application stack and,
or heap.
Monitors events and state changes in the SoC and handles security
violations. Currently checks for:
Applications can write to these registers to define the area and then
enable the monitor. One enabled, the monitor can't be disabled, and
the ADDR_CPU_MON_FIRST and ADDR_CPU_MON_LAST registers can't be
changes. This means that an application that wants to use the monitor
1. Trying to execute instructions in FW_RAM. *Always enabled.*
2. Trying to access RAM outside of the physical memory. *Always enabled*
3. Trying to execute instructions from a memory area in RAM defined by
the application.
Number 1 and 2 are always enabled. Number 3 is set and enabled by the
device application. Once enabled, by writing to ADDR_CPU_MON_CTRL, the
memory defined by ADDR_CPU_MON_FIRST and ADDR_CPU_MON_LAST will be
protected against execution. Typically the application developer will
set this protection to cover the application stack and/or heap.
An application can write to these registers to define the area and
then enable the monitor. Once enabled the monitor can't be disabled,
and the ADDR_CPU_MON_FIRST and ADDR_CPU_MON_LAST registers can't be
changed. This means that an application that wants to use the monitor
must define the area first before enabling the monitor.
Once enabled, if the CPU tries to read an instruction from the defined
area, the core will force the CPU to instead read an all zero, illegal
instruction. This illegal instruction will trigger the CPU to enter
its TRAP state, from which it can't returned unless the TKey is power
cycled.
area, the core will force the CPU to instead read an all zero, which
is an illegal instruction. This illegal instruction will trigger the
CPU to enter its TRAP state, from which it can't return unless the
TKey is power cycled.
The FW will not write to these registers as part of loading an
The firmware will not write to these registers as part of loading an
app. The app developer must define the area and enable the monitor to
get the protection.
Note that there is a second memory area that is under the protection
of the execution monitor - the FW_RAM. The execution protection of
this memory is always anabled and the definition of the area is hard
coded into the FPGA design.
One feature not obvious from the API is that when the CPU traps, the
core will detect that and start flashing the RGB LED with a red
light - indicating that the CPU is its trap state and no further
One feature not obvious from the API is that when the CPU traps the
core will detect that and start flashing the status LED with a red
light indicating that the CPU is in a trapped state and no further
execution is possible.
## Implementation
The core is implemented as a single module. Future versions will

35
hw/application_fpga/core/tk1/rtl/tk1.v
View File

@ -325,23 +325,40 @@ module tk1(
//----------------------------------------------------------------
// cpu_monitor
// security_monitor
//
// Monitor events and state changes in the SoC, and handle
// security violations. We currently check for:
//
// Any access to RAM but outside of the size of the physical mem.
//
// Trying to execute instructions in FW-RAM.
//
// Trying to execute code in mem area set to be data access only.
// This requires execution monitor to have been setup and
// enabled.
//----------------------------------------------------------------
always @*
begin : cpu_monitor
begin : security_monitor
force_trap_set = 1'h0;
if (cpu_valid && cpu_instr) begin
if ((cpu_addr >= FW_RAM_FIRST) &&
(cpu_addr <= FW_RAM_LAST)) begin
force_trap_set = 1'h1;
if (cpu_valid) begin
if (cpu_addr[31 : 30] == 2'h01 & |cpu_addr[29 : 17]) begin
force_trap_set = 1'h1;
end
if (cpu_mon_en_reg) begin
if ((cpu_addr >= cpu_mon_first_reg) &&
(cpu_addr <= cpu_mon_last_reg)) begin
if (cpu_instr) begin
if ((cpu_addr >= FW_RAM_FIRST) &&
(cpu_addr <= FW_RAM_LAST)) begin
force_trap_set = 1'h1;
end
if (cpu_mon_en_reg) begin
if ((cpu_addr >= cpu_mon_first_reg) &&
(cpu_addr <= cpu_mon_last_reg)) begin
force_trap_set = 1'h1;
end
end
end
end
end