[PATCH] target/arm: Fix ISR_EL1 tracking when executing at EL2

[Marc Zyngier <maz@kernel.org>]

The ARMv8 ARM states when executing at EL2, EL3 or Secure EL1,
ISR_EL1 shows the pending status of the physical IRQ, FIQ, or
SError interrupts.

Unfortunately, QEMU's implementation only considers the HCR_EL2
bits, and ignores the current exception level. This means a hypervisor
trying to look at its own interrupt state actually sees the guest
state, which is unexpected and breaks KVM as of Linux 5.3.

Instead, check for the running EL and return the physical bits
if not running in a virtualized context.

Fixes: 636540e9c40b
Reported-by: Quentin Perret <qperret@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 target/arm/helper.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/target/arm/helper.c b/target/arm/helper.c
index a089fb5a69..027fffbff6 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -1934,8 +1934,11 @@ static uint64_t isr_read(CPUARMState *env, const ARMCPRegInfo *ri)
     CPUState *cs = env_cpu(env);
     uint64_t hcr_el2 = arm_hcr_el2_eff(env);
     uint64_t ret = 0;
+    bool allow_virt = (arm_current_el(env) == 1 &&
+                       (!arm_is_secure_below_el3(env) ||
+                        (env->cp15.scr_el3 & SCR_EEL2)));
 
-    if (hcr_el2 & HCR_IMO) {
+    if (allow_virt && (hcr_el2 & HCR_IMO)) {
         if (cs->interrupt_request & CPU_INTERRUPT_VIRQ) {
             ret |= CPSR_I;
         }
@@ -1945,7 +1948,7 @@ static uint64_t isr_read(CPUARMState *env, const ARMCPRegInfo *ri)
         }
     }
 
-    if (hcr_el2 & HCR_FMO) {
+    if (allow_virt && (hcr_el2 & HCR_FMO)) {
         if (cs->interrupt_request & CPU_INTERRUPT_VFIQ) {
             ret |= CPSR_F;
         }
-- 
2.17.1