[Qemu-devel] [PATCH 11/20] target/arm: Add support for restoring v8M additional state context

[Peter Maydell <peter.maydell@linaro.org>]

For v8M, exceptions from Secure to Non-Secure state will save
callee-saved registers to the exception frame as well as the
caller-saved registers. Add support for unstacking these
registers in exception exit when necessary.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 target/arm/helper.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/target/arm/helper.c b/target/arm/helper.c
index da3a36e..25f5675 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -6453,6 +6453,36 @@ static void do_v7m_exception_exit(ARMCPU *cpu)
                           "for destination state is UNPREDICTABLE\n");
         }
 
+        /* Do we need to pop callee-saved registers? */
+        if (return_to_secure &&
+            ((excret & R_V7M_EXCRET_ES_MASK) == 0 ||
+             (excret & R_V7M_EXCRET_DCRS_MASK) == 0)) {
+            uint32_t expected_sig = 0xfefa125b;
+            uint32_t actual_sig = ldl_phys(cs->as, frameptr);
+
+            if (expected_sig != actual_sig) {
+                /* Take a SecureFault on the current stack */
+                env->v7m.sfsr |= R_V7M_SFSR_INVIS_MASK;
+                armv7m_nvic_set_pending(env->nvic, ARMV7M_EXCP_SECURE, false);
+                v7m_exception_taken(cpu, excret);
+                qemu_log_mask(CPU_LOG_INT, "...taking SecureFault on existing "
+                              "stackframe: failed exception return integrity "
+                              "signature check\n");
+                return;
+            }
+
+            env->regs[4] = ldl_phys(cs->as, frameptr + 0x8);
+            env->regs[5] = ldl_phys(cs->as, frameptr + 0xc);
+            env->regs[6] = ldl_phys(cs->as, frameptr + 0x10);
+            env->regs[7] = ldl_phys(cs->as, frameptr + 0x14);
+            env->regs[8] = ldl_phys(cs->as, frameptr + 0x18);
+            env->regs[9] = ldl_phys(cs->as, frameptr + 0x1c);
+            env->regs[10] = ldl_phys(cs->as, frameptr + 0x20);
+            env->regs[11] = ldl_phys(cs->as, frameptr + 0x24);
+
+            frameptr += 0x28;
+        }
+
         /* Pop registers. TODO: make these accesses use the correct
          * attributes and address space (S/NS, priv/unpriv) and handle
          * memory transaction failures.
-- 
2.7.4