On 06/27/2014 12:30 PM, Doug Anderson wrote: > Stephen, > > On Fri, Jun 27, 2014 at 11:20 AM, Stephen Warren <swarren@xxxxxxxxxxxxx> wrote: >> On 06/27/2014 10:45 AM, Doug Anderson wrote: >>> Stephen, >>> >>> On Fri, Jun 27, 2014 at 9:10 AM, Stephen Warren <swarren@xxxxxxxxxxxxx> wrote: >>>> Surely there's a driver (or could be a driver) for the TPM chip, and >>>> that driver should have a reset-mask-gpios property, so the driver can >>>> call gpio_get() and gpio_set_output() on the GPIO? >>>> >>>> Faking this out via a not-really-a-regulator or pinctrl hogs seems like >>>> an abuse of those features to me. ... >> As an aside, why do we even care about this? The kernel clearly can >> unlock the TPM simply by failing to set the GPIO up correctly, so at >> best this is security through obscurity. If someone actively wanted to >> do something bad to the TPM, they'd simply comment out this piece of >> code in the kernel. At least that's true with usptream kernels which >> aren't validated at all during boot. For a downstream signed kernel, >> perhaps this patch makes sense (although I haven't thought about all the >> security angles), but then it'd make sense to keep this patch downstream. > > Check out the bullet point about the firmware checking for kernel > cheats. At resume time the chip actually re-loads read only firmware > out of SPI flash (no choice about this). This read only firmware can > check the state of the mask pin (which is preserved across sleep wake) > to see if the kernel cheated. Ah, that covers the security issues then. I'd argue that the RO firmware should be setting up GPIOs like this myself (and the pinmux, from a nice big table), and the kernel simply not touch it all since it has no direct use for the pin. But I suppose if the firmware is already baked and read only, that's not possible. -- To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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