Missing Ability to Patch ROM Code
Missing an ability to patch ROM code may leave a System or System-on-Chip (SoC) in a vulnerable state.
Description
A System or System-on-Chip (SoC) that implements a boot process utilizing security mechanisms such as Root-of-Trust (RoT) typically starts by executing code from a Read-only-Memory (ROM) component. The code in ROM is immutable, hence any security vulnerabilities discovered in the ROM code can never be fixed for the systems that are already in use.
A common weakness is that the ROM does not have the ability to patch if security vulnerabilities are uncovered after the system gets shipped. This leaves the system in a vulnerable state where an adversary can compromise the SoC.
Demonstrations
The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.
Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.
Example One
A System-on-Chip (SOC) implements a Root-of-Trust (RoT) in ROM to boot secure code. However, at times this ROM code might have security vulnerabilities and need to be patched. Since ROM is immutable, it can be impossible to patch.
ROM does not have built-in application-programming interfaces (APIs) to patch if the code is vulnerable. Implement mechanisms to patch the vulnerable ROM code.
Example Two
The example code is taken from the SoC peripheral wrapper inside the buggy OpenPiton SoC of HACK@DAC'21. The wrapper is used for connecting the communications between SoC peripherals, such as crypto-engines, direct memory access (DMA), reset controllers, JTAG, etc. The secure implementation of the SoC wrapper should allow users to boot from a ROM for Linux (i_bootrom_linux) or from a patchable ROM (i_bootrom_patch) if the Linux bootrom has security or functional issues.The example code is taken from the SoC peripheral wrapper inside the buggy OpenPiton SoC of HACK@DAC'21. The wrapper is used for connecting the communications between SoC peripherals, such as crypto-engines, direct memory access (DMA), reset controllers, JTAG, etc. The secure implementation of the SoC wrapper should allow users to boot from a ROM for Linux (i_bootrom_linux) or from a patchable ROM (i_bootrom_patch) if the Linux bootrom has security or functional issues.
...
bootrom i_bootrom_patch (
.clk_i ,
.req_i ( rom_req ),
.addr_i ( rom_addr ),
.rdata_o ( rom_rdata_patch )
);
bootrom_linux i_bootrom_linux (
.clk_i ,
.req_i ( rom_req ),
.addr_i ( rom_addr ),
.rdata_o ( rom_rdata_linux )
);
assign rom_rdata = (ariane_boot_sel_i) ? rom_rdata_linux : rom_rdata_linux;
...The above implementation causes the ROM data to be hardcoded for the linux system (rom_rdata_linux) regardless of the value of ariane_boot_sel_i. Therefore, the data (rom_rdata_patch) from the patchable ROM code is never used [REF-1396].
This weakness disables the ROM's ability to be patched. If attackers uncover security vulnerabilities in the ROM, the users must replace the entire device. Otherwise, the weakness exposes the system to a vulnerable state forever.
A fix to this issue is to enable rom_rdata to be selected from the patchable rom (rom_rdata_patch) [REF-1397].
...
bootrom i_bootrom_patch (
.clk_i ,
.req_i ( rom_req ),
.addr_i ( rom_addr ),
.rdata_o ( rom_rdata_patch )
);
bootrom_linux i_bootrom_linux (
.clk_i ,
.req_i ( rom_req ),
.addr_i ( rom_addr ),
.rdata_o ( rom_rdata_linux )
);
assign rom_rdata = (ariane_boot_sel_i) ? rom_rdata_patch : rom_rdata_linux;
...See Also
Weaknesses in this category are related to resource control.
Weaknesses in this category are related to improper design of full-system security flows, including but not limited to secure boot, secure update, and hardware-device ...
This view (slice) covers all the elements in CWE.
This view (slice) lists weaknesses that can be introduced during implementation.
This view (slice) lists weaknesses that can be introduced during design.
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