diff options
author | Brian Norris <computersforpeace@gmail.com> | 2016-01-29 11:25:33 -0800 |
---|---|---|
committer | Brian Norris <computersforpeace@gmail.com> | 2016-03-07 18:01:55 -0800 |
commit | 47b8edbf0d43dcb9fda83833c05470edf59c31e3 (patch) | |
tree | 49a92a61be05c18d2ee226bdd30fd35240cc5f3b /drivers/mtd/spi-nor/spi-nor.c | |
parent | f8860802da84aa2bbc9f316e549a349fb40cda63 (diff) |
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>
Diffstat (limited to 'drivers/mtd/spi-nor/spi-nor.c')
-rw-r--r-- | drivers/mtd/spi-nor/spi-nor.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c index 680bc1510475..6fcd9d7589f8 100644 --- a/drivers/mtd/spi-nor/spi-nor.c +++ b/drivers/mtd/spi-nor/spi-nor.c @@ -540,6 +540,9 @@ static int stm_lock(struct spi_nor *nor, loff_t ofs, uint64_t len) status_new = (status_old & ~mask) | val; + /* Disallow further writes if WP pin is asserted */ + status_new |= SR_SRWD; + /* Don't bother if they're the same */ if (status_new == status_old) return 0; @@ -605,6 +608,10 @@ static int stm_unlock(struct spi_nor *nor, loff_t ofs, uint64_t len) status_new = (status_old & ~mask) | val; + /* Don't protect status register if we're fully unlocked */ + if (lock_len == mtd->size) + status_new &= ~SR_SRWD; + /* Don't bother if they're the same */ if (status_new == status_old) return 0; |