| Message ID | 20230921080301.253563-10-gatien.chevallier@foss.st.com (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | Herbert Xu |
| Headers | show |
| Series | hwrng: stm32: support STM32MP13x platforms | expand |
Gatien Chevallier <gatien.chevallier@foss.st.com> writes: > The RNG on STM32MP13 offers upgrades like customization of its > configuration and the conditional reset. > > The hardware RNG should be managed in the secure world for but it > is supported on Linux. Therefore, is it not default enabled. Just curious, will there be concurrent access? If yes, how do you manage the entropy in that case? If you allow access to RNG from normal world, can attacker change the setting to generate more predicatable numbers leading this to secure world as well. I understand that you're leaving the enablement part to customer but you still have to allow RNG access to normal world for that. -Kamlesh
Hi Kamlesh, On 9/22/23 10:20, Kamlesh Gurudasani wrote: > Gatien Chevallier <gatien.chevallier@foss.st.com> writes: > >> The RNG on STM32MP13 offers upgrades like customization of its >> configuration and the conditional reset. >> >> The hardware RNG should be managed in the secure world for but it >> is supported on Linux. Therefore, is it not default enabled. > Just curious, will there be concurrent access? If yes, how do you manage > the entropy in that case? > Any read on the data register leads to its refreshment. There can be only one access at a time at the bus level. The rest (FIFO is empty after request, etc...) is managed by the code in this patchset. > If you allow access to RNG from normal world, can attacker change the > setting to generate more predicatable numbers leading this to secure > world as well. > > I understand that you're leaving the enablement part to customer but > you still have to allow RNG access to normal world for that. > > -Kamlesh If RNG is secure, then it should be managed by the secure world and accessed via some interface. Ours is OP-TEE RNG PTA. The secure level of the peripheral is managed by the ETZPC, which manages the security configuration of the board's peripherals. If the RNG is assigned to the non-secure world, then yes, the non-secure world can access the RNG configuration. Now, your question is: what happens to the secure world in such case? The answer is that it should run on a pseudo-random software RNG seeded at boot by the hardware RNG. So there's no link anymore if non-secure world deteriorates the hardware RNG configuration. Of course, if such choice is made, it's up to the customer to see the whole picture. Best regards, Gatien
diff --git a/arch/arm/boot/dts/st/stm32mp131.dtsi b/arch/arm/boot/dts/st/stm32mp131.dtsi index ac90fcbf0c09..39db82b782eb 100644 --- a/arch/arm/boot/dts/st/stm32mp131.dtsi +++ b/arch/arm/boot/dts/st/stm32mp131.dtsi @@ -1220,6 +1220,14 @@ mdma: dma-controller@58000000 { dma-requests = <48>; }; + rng: rng@54004000 { + compatible = "st,stm32mp13-rng"; + reg = <0x54004000 0x400>; + clocks = <&rcc RNG1_K>; + resets = <&rcc RNG1_R>; + status = "disabled"; + }; + fmc: memory-controller@58002000 { compatible = "st,stm32mp1-fmc2-ebi"; reg = <0x58002000 0x1000>;
The RNG on STM32MP13 offers upgrades like customization of its configuration and the conditional reset. The hardware RNG should be managed in the secure world for but it is supported on Linux. Therefore, is it not default enabled. Signed-off-by: Gatien Chevallier <gatien.chevallier@foss.st.com> --- arch/arm/boot/dts/st/stm32mp131.dtsi | 8 ++++++++ 1 file changed, 8 insertions(+)