mtd: spi-nor: disallow further writes to SR if WP# is low
Locking the flash is most useful if it provides real hardware security.
Otherwise, it's little more than a software permission bit.
A reasonable use case that provides real HW security might be like
follows:
(1) hardware WP# is deasserted
(2) program flash
(3) flash range is protected via status register
(4) hardware WP# is asserted
(5) flash protection range can no longer be changed, until WP# is
deasserted
In this way, flash protection is co-owned by hardware and software.
Now, one would expect to be able to perform step (3) with
ioctl(MEMLOCK), except that the spi-nor driver does not set the Status
Register Protect bit (a.k.a. Status Register Write Disable (SRWD)), so
even though the range is now locked, it does not satisfy step (5) -- it
can still be changed by a call to ioctl(MEMUNLOCK).
So, let's enable status register protection after the first lock
command, and disable protection only when the flash is fully unlocked.
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Tested-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
1 file changed