As per DDI0487 R_TYTWB GCS adds an additional case where an illegal
exception return can be generated. If all of:
- PSTATE.EXLOCK is 0.
- The EL is not being changed by the ERET.
- GCSCR_ELx.EXLOCKEN is 1.
are true then the return is illegal. Emulate this behaviour when
emulating ERET for nested guests.
Signed-off-by: Mark Brown <broo...@kernel.org>
---
arch/arm64/kvm/emulate-nested.c | 40 +++++++++++++++++++++++++++++++++++++++-
1 file changed, 39 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/kvm/emulate-nested.c b/arch/arm64/kvm/emulate-nested.c
index 90cb4b7ae0ff..9b02b85eda64 100644
--- a/arch/arm64/kvm/emulate-nested.c
+++ b/arch/arm64/kvm/emulate-nested.c
@@ -2632,6 +2632,41 @@ bool forward_debug_exception(struct kvm_vcpu *vcpu)
return forward_mdcr_traps(vcpu, MDCR_EL2_TDE);
}
+/*
+ * A subset of the pseudocode ELFromSPSR(), validity checks are
+ * assumed to have been done in code that is not GCS specific.
+ */
+static inline int exlock_el_from_spsr(u64 spsr)
+{
+ return FIELD_GET(GENMASK(3, 2), spsr);
+}
+
+/* See IllegalExceptionReturn() pseudocode */
+static bool kvm_check_illegal_exlock_return(struct kvm_vcpu *vcpu, u64 spsr)
+{
+ u64 cur_el, target_el;
+ u64 gcscr;
+
+ if (!kvm_has_gcs(vcpu->kvm))
+ return false;
+
+ if (spsr & PSR_EXLOCK_BIT)
+ return false;
+
+ cur_el = exlock_el_from_spsr(vcpu->arch.ctxt.regs.pstate);
+ target_el = exlock_el_from_spsr(spsr);
+
+ if (cur_el != target_el)
+ return false;
+
+ if (vcpu_is_el2(vcpu))
+ gcscr = __vcpu_sys_reg(vcpu, GCSCR_EL2);
+ else
+ gcscr = __vcpu_sys_reg(vcpu, GCSCR_EL1);
+
+ return gcscr & GCSCR_ELx_EXLOCKEN;
+}
+
static u64 kvm_check_illegal_exception_return(struct kvm_vcpu *vcpu, u64 spsr)
{
u64 mode = spsr & PSR_MODE_MASK;
@@ -2642,12 +2677,15 @@ static u64 kvm_check_illegal_exception_return(struct
kvm_vcpu *vcpu, u64 spsr)
* - trying to return to an illegal M value
* - trying to return to a 32bit EL
* - trying to return to EL1 with HCR_EL2.TGE set
+ * - GCSCR_ELx.EXLOCKEN is 1 and PSTATE.EXLOCK is 0 when attempting
+ * to return from ELx the same EL.
*/
if (mode == PSR_MODE_EL3t || mode == PSR_MODE_EL3h ||
mode == 0b00001 || (mode & BIT(1)) ||
(spsr & PSR_MODE32_BIT) ||
(vcpu_el2_tge_is_set(vcpu) && (mode == PSR_MODE_EL1t ||
- mode == PSR_MODE_EL1h))) {
+ mode == PSR_MODE_EL1h)) ||
+ kvm_check_illegal_exlock_return(vcpu, spsr)) {
/*
* The guest is playing with our nerves. Preserve EL, SP,
* masks, flags from the existing PSTATE, and set IL.
--
2.47.2
