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().
Mess with ELR_EL2 directly?
Thanks,
James
> + }
> +
> /*
> * We're using the raw exception code in order to only process
> * the trap if no SError is pending. We will come back to the
>
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