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Julius Werner authored
The recent coreboot memory console update (firmware: google: memconsole: Adapt to new coreboot ring buffer format) introduced a small security issue in the driver: The new driver implementation parses the memory console structure again on every access. This is intentional so that additional lines added concurrently by runtime firmware can be read out. However, if an attacker can write to the structure, they could increase the size value to a point where the driver would read potentially sensitive memory areas from outside the original console buffer during the next access. This can be done through /dev/mem, since the console buffer usually resides in firmware-reserved memory that is not covered by STRICT_DEVMEM. This patch resolves that problem by reading the buffer's size value only once during boot (where we can still trust the structure). Other parts of the structure can still be modified at runtime, but the driver's bounds checks make sure that it will never read outside the buffer. Fixes: a5061d02 ("firmware: google: memconsole: Adapt to new coreboot ring buffer format") Signed-off-by: Julius Werner <jwerner@chromium.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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