feat(fvp): emulate trapped RNDR
When a platform decides to use FEAT_RNG_TRAP, every RNDR or RNDRSS read
will trap into EL3. The platform can then emulate those instructions, by
either executing the real CPU instructions, potentially conditioning the
results, or use rate-limiting or filtering to protect the hardware
entropy pool. Another possiblitiy would be to use some platform specific
TRNG device to get entropy and returning this.
To demonstrate platform specific usage, add a demo implementation for the
FVP: It will execute the actual CPU instruction and just return the
result. This should serve as reference code to implement platform specific
policies.
We change the definition of read_rndr() and read_rndrrs() to use the
alternative sysreg encoding, so that all assemblers can handle that.
Add documentation about the new platform specific RNG handler function.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Change-Id: Ibce817b3b06ad20129d15531b81402e3cc3e9a9e
diff --git a/include/bl31/sync_handle.h b/include/bl31/sync_handle.h
index 6ff88f9..e211575 100644
--- a/include/bl31/sync_handle.h
+++ b/include/bl31/sync_handle.h
@@ -15,6 +15,9 @@
#define ISS_SYSREG_REG_SHIFT 5U
#define ISS_SYSREG_DIRECTION_MASK 0x000001UL
+#define ISS_SYSREG_OPCODE_RNDR 0x30c808U
+#define ISS_SYSREG_OPCODE_RNDRRS 0x32c808U
+
#define TRAP_RET_UNHANDLED -1
#define TRAP_RET_REPEAT 0
#define TRAP_RET_CONTINUE 1
@@ -50,6 +53,9 @@
*/
int handle_sysreg_trap(uint64_t esr_el3, cpu_context_t *ctx);
+/* Prototypes for system register emulation handlers provided by platforms. */
+int plat_handle_rng_trap(uint64_t esr_el3, cpu_context_t *ctx);
+
#endif /* __ASSEMBLER__ */
#endif