1*19d54020SJack RosenthalWhat: /sys/bus/coreboot 2*19d54020SJack RosenthalDate: August 2022 3*19d54020SJack RosenthalContact: Jack Rosenthal <jrosenth@chromium.org> 4*19d54020SJack RosenthalDescription: 5*19d54020SJack Rosenthal The coreboot bus provides a variety of virtual devices used to 6*19d54020SJack Rosenthal access data structures created by the Coreboot BIOS. 7*19d54020SJack Rosenthal 8*19d54020SJack RosenthalWhat: /sys/bus/coreboot/devices/cbmem-<id> 9*19d54020SJack RosenthalDate: August 2022 10*19d54020SJack RosenthalContact: Jack Rosenthal <jrosenth@chromium.org> 11*19d54020SJack RosenthalDescription: 12*19d54020SJack Rosenthal CBMEM is a downwards-growing memory region created by Coreboot, 13*19d54020SJack Rosenthal and contains tagged data structures to be shared with payloads 14*19d54020SJack Rosenthal in the boot process and the OS. Each CBMEM entry is given a 15*19d54020SJack Rosenthal directory in /sys/bus/coreboot/devices based on its id. 16*19d54020SJack Rosenthal A list of ids known to Coreboot can be found in the coreboot 17*19d54020SJack Rosenthal source tree at 18*19d54020SJack Rosenthal ``src/commonlib/bsd/include/commonlib/bsd/cbmem_id.h``. 19*19d54020SJack Rosenthal 20*19d54020SJack RosenthalWhat: /sys/bus/coreboot/devices/cbmem-<id>/address 21*19d54020SJack RosenthalDate: August 2022 22*19d54020SJack RosenthalContact: Jack Rosenthal <jrosenth@chromium.org> 23*19d54020SJack RosenthalDescription: 24*19d54020SJack Rosenthal This is the pyhsical memory address that the CBMEM entry's data 25*19d54020SJack Rosenthal begins at, in hexadecimal (e.g., ``0x76ffe000``). 26*19d54020SJack Rosenthal 27*19d54020SJack RosenthalWhat: /sys/bus/coreboot/devices/cbmem-<id>/size 28*19d54020SJack RosenthalDate: August 2022 29*19d54020SJack RosenthalContact: Jack Rosenthal <jrosenth@chromium.org> 30*19d54020SJack RosenthalDescription: 31*19d54020SJack Rosenthal This is the size of the CBMEM entry's data, in hexadecimal 32*19d54020SJack Rosenthal (e.g., ``0x1234``). 33*19d54020SJack Rosenthal 34*19d54020SJack RosenthalWhat: /sys/bus/coreboot/devices/cbmem-<id>/mem 35*19d54020SJack RosenthalDate: August 2022 36*19d54020SJack RosenthalContact: Jack Rosenthal <jrosenth@chromium.org> 37*19d54020SJack RosenthalDescription: 38*19d54020SJack Rosenthal A file exposing read/write access to the entry's data. Note 39*19d54020SJack Rosenthal that this file does not support mmap(), as coreboot 40*19d54020SJack Rosenthal does not guarantee that the data will be page-aligned. 41*19d54020SJack Rosenthal 42*19d54020SJack Rosenthal The mode of this file is 0600. While there shouldn't be 43*19d54020SJack Rosenthal anything security-sensitive contained in CBMEM, read access 44*19d54020SJack Rosenthal requires root privileges given this is exposing a small subset 45*19d54020SJack Rosenthal of physical memory. 46