From 097d68ac2fd9bd40d0b6a3b3992c86a1f79d7187 Mon Sep 17 00:00:00 2001 From: Peter Maydell Date: Wed, 12 Mar 2025 13:25:08 +0000 Subject: [PATCH] target/arm: Forbid return to AArch32 when CPU is AArch64-only In the Arm ARM, rule R_TYTWB states that returning to AArch32 is an illegal exception return if: * AArch32 is not supported at any exception level * the target EL is configured for AArch64 via SCR_EL3.RW or HCR_EL2.RW or via CPU state at reset We check the second of these, but not the first (which can only be relevant for the case of a return to EL0, because if AArch32 is not supported at one of the higher ELs then the RW bits will have an effective value of 1 and the the "configured for AArch64" condition will hold also). Add the missing condition. Although this is technically a bug (because we have one AArch64-only CPU: a64fx) it isn't worth backporting to stable because no sensible guest code will deliberately try to return to a nonexistent execution state to check that it gets an illegal exception return. Signed-off-by: Peter Maydell Reviewed-by: Richard Henderson --- target/arm/tcg/helper-a64.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/target/arm/tcg/helper-a64.c b/target/arm/tcg/helper-a64.c index e2bdf07833..9244848efe 100644 --- a/target/arm/tcg/helper-a64.c +++ b/target/arm/tcg/helper-a64.c @@ -678,6 +678,11 @@ void HELPER(exception_return)(CPUARMState *env, uint64_t new_pc) goto illegal_return; } + if (!return_to_aa64 && !cpu_isar_feature(aa64_aa32, cpu)) { + /* Return to AArch32 when CPU is AArch64-only */ + goto illegal_return; + } + if (new_el == 1 && (arm_hcr_el2_eff(env) & HCR_TGE)) { goto illegal_return; } -- 2.39.5