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authorBrian Norris <computersforpeace@gmail.com>2016-01-29 11:25:33 -0800
committerBrian Norris <computersforpeace@gmail.com>2016-03-07 18:01:55 -0800
commit47b8edbf0d43dcb9fda83833c05470edf59c31e3 (patch)
tree49a92a61be05c18d2ee226bdd30fd35240cc5f3b /drivers/mtd/spi-nor
parentf8860802da84aa2bbc9f316e549a349fb40cda63 (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')
-rw-r--r--drivers/mtd/spi-nor/spi-nor.c7
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;