Re: [PATCH 04/11] KVM: arm64: Move PC rollback on SError to HYP
From: James Morse <james.morse@arm.com>
Date: 2020-10-27 14:57:38
Also in:
kvm, kvmarm
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.
quoted hunk ↗ jump to hunk
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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