| 1 | What: /sys/bus/coreboot |
| 2 | Date: August 2022 |
| 3 | Contact: Jack Rosenthal <[email protected]> |
| 4 | Description: |
| 5 | The coreboot bus provides a variety of virtual devices used to |
| 6 | access data structures created by the Coreboot BIOS. |
| 7 | |
| 8 | What: /sys/bus/coreboot/devices/cbmem-<id> |
| 9 | Date: August 2022 |
| 10 | Contact: Jack Rosenthal <[email protected]> |
| 11 | Description: |
| 12 | CBMEM is a downwards-growing memory region created by Coreboot, |
| 13 | and contains tagged data structures to be shared with payloads |
| 14 | in the boot process and the OS. Each CBMEM entry is given a |
| 15 | directory in /sys/bus/coreboot/devices based on its id. |
| 16 | A list of ids known to Coreboot can be found in the coreboot |
| 17 | source tree at |
| 18 | ``src/commonlib/bsd/include/commonlib/bsd/cbmem_id.h``. |
| 19 | |
| 20 | What: /sys/bus/coreboot/devices/cbmem-<id>/address |
| 21 | Date: August 2022 |
| 22 | Contact: Jack Rosenthal <[email protected]> |
| 23 | Description: |
| 24 | This is the physical memory address that the CBMEM entry's data |
| 25 | begins at, in hexadecimal (e.g., ``0x76ffe000``). |
| 26 | |
| 27 | What: /sys/bus/coreboot/devices/cbmem-<id>/size |
| 28 | Date: August 2022 |
| 29 | Contact: Jack Rosenthal <[email protected]> |
| 30 | Description: |
| 31 | This is the size of the CBMEM entry's data, in hexadecimal |
| 32 | (e.g., ``0x1234``). |
| 33 | |
| 34 | What: /sys/bus/coreboot/devices/cbmem-<id>/mem |
| 35 | Date: August 2022 |
| 36 | Contact: Jack Rosenthal <[email protected]> |
| 37 | Description: |
| 38 | A file exposing read/write access to the entry's data. Note |
| 39 | that this file does not support mmap(), as coreboot |
| 40 | does not guarantee that the data will be page-aligned. |
| 41 | |
| 42 | The mode of this file is 0600. While there shouldn't be |
| 43 | anything security-sensitive contained in CBMEM, read access |
| 44 | requires root privileges given this is exposing a small subset |
| 45 | of physical memory. |