On 2020-10-27 14:56, James Morse wrote:
Hi Marc,
On 26/10/2020 13:34, Marc Zyngier wrote:
Instead of handling the "PC rollback on SError during HVC" at EL1
(which
requires disclosing PC to a potentially untrusted kernel), let's move
this fixup to ... fixup_guest_exit(), which is where we do all fixups.
diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h
b/arch/arm64/kvm/hyp/include/hyp/switch.h
index d687e574cde5..668f02c7b0b3 100644
--- a/arch/arm64/kvm/hyp/include/hyp/switch.h
+++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
@@ -411,6 +411,21 @@ static inline bool fixup_guest_exit(struct
kvm_vcpu *vcpu, u64 *exit_code)
if (ARM_EXCEPTION_CODE(*exit_code) != ARM_EXCEPTION_IRQ)
vcpu->arch.fault.esr_el2 = read_sysreg_el2(SYS_ESR);
+ if (ARM_SERROR_PENDING(*exit_code)) {
+ u8 esr_ec = kvm_vcpu_trap_get_class(vcpu);
+
+ /*
+ * HVC already have an adjusted PC, which we need to
+ * correct in order to return to after having injected
+ * the SError.
+ *
+ * SMC, on the other hand, is *trapped*, meaning its
+ * preferred return address is the SMC itself.
+ */
+ if (esr_ec == ESR_ELx_EC_HVC32 || esr_ec == ESR_ELx_EC_HVC64)
+ *vcpu_pc(vcpu) -= 4;
Isn't *vcpu_pc(vcpu) the PC of the previous entry for this vcpu?....
its not the PC of the
exit until __sysreg_save_el2_return_state() saves it, which happens
just after
fixup_guest_exit().
Hmmm. Good point. The move was obviously done in haste, thank you for
pointing
this blatant bug.
Mess with ELR_EL2 directly?
Yes, that's the best course of action. We never run this code anyway.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
