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: a5061d028 ("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>
The upstream coreboot implementation of memconsole was enhanced from a
single-boot console to a persistent ring buffer
(https://review.coreboot.org/#/c/18301). This patch changes the kernel
memconsole driver to be able to read the new format in all cases.
Signed-off-by: Julius Werner <jwerner@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This patch redesigns the interface between the generic memconsole driver
and its implementations to become more flexible than a flat memory
buffer with unchanging bounds. This allows memconsoles like coreboot's
to include lines that were added by runtime firmware after the driver
was initialized. Since the console log size is thus no longer static,
this means that the /sys/firmware/log file has to become unseekable.
Signed-off-by: Julius Werner <jwerner@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
In case of error, the function platform_device_register_simple() returns
ERR_PTR() and never returns NULL. The NULL test in the return value
check should be replaced with IS_ERR().
Fixes: d384d6f43d ("firmware: google memconsole: Add coreboot support")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Coreboot (http://www.coreboot.org) allows to save the firmware console
output in a memory buffer. With this patch, the address of this memory
buffer is obtained from coreboot tables on x86 chromebook devices
declaring an ACPI device with name matching GOOGCB00 or BOOT0000.
If the memconsole-coreboot driver is able to find the coreboot table,
the memconsole driver sets the cbmem_console address and initializes the
memconsole sysfs entries.
The coreboot_table-acpi driver is responsible for setting the address of
the coreboot table header when probed. If this address is not yet set
when memconsole-coreboot is probed, then the probe is deferred by
returning -EPROBE_DEFER.
This patch is a rework/split/merge of patches from the chromeos v4.4
kernel tree originally authored by:
Vadim Bendebury <vbendeb@chromium.org>
Wei-Ning Huang <wnhuang@google.com>
Yuji Sasaki <sasakiy@google.com>
Duncan Laurie <dlaurie@chromium.org>
Julius Werner <jwerner@chromium.org>
Brian Norris <briannorris@chromium.org>
Signed-off-by: Thierry Escande <thierry.escande@collabora.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
