On 28 January 2016 at 02:51, Brian Norris <[email protected]> wrote: > 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. > > Signed-off-by: Brian Norris <[email protected]> > --- > drivers/mtd/spi-nor/spi-nor.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c > index 3a08aa53c171..46da6bb706fa 100644 > --- a/drivers/mtd/spi-nor/spi-nor.c > +++ b/drivers/mtd/spi-nor/spi-nor.c > @@ -518,6 +518,9 @@ 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; > +
No need to clear SR_SRWD in stm_unlock? -- Ezequiel García, VanguardiaSur www.vanguardiasur.com.ar
