On Mon, Feb 26, 2024 at 10:06:00AM +0000, Marc Zyngier wrote:
> Now that we have some emulation in place for ERETA[AB], we can
> plug it into the exception handling machinery.
>
> As for a bare ERET, an "easy" ERETAx instruction is processed as
> a fixup, while something that requires a translation regime
> transition or an exception delivery is left to the slow path.
>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> ---
> arch/arm64/kvm/emulate-nested.c | 22 ++++++++++++++++++++--
> arch/arm64/kvm/handle_exit.c | 3 ++-
> arch/arm64/kvm/hyp/vhe/switch.c | 13 +++++++++++--
> 3 files changed, 33 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/kvm/emulate-nested.c b/arch/arm64/kvm/emulate-nested.c
> index 63a74c0330f1..72d733c74a38 100644
> --- a/arch/arm64/kvm/emulate-nested.c
> +++ b/arch/arm64/kvm/emulate-nested.c
> @@ -2172,7 +2172,7 @@ static u64 kvm_check_illegal_exception_return(struct kvm_vcpu *vcpu, u64 spsr)
>
> void kvm_emulate_nested_eret(struct kvm_vcpu *vcpu)
> {
> - u64 spsr, elr;
> + u64 spsr, elr, esr;
>
> /*
> * Forward this trap to the virtual EL2 if the virtual
> @@ -2181,12 +2181,30 @@ void kvm_emulate_nested_eret(struct kvm_vcpu *vcpu)
> if (forward_traps(vcpu, HCR_NV))
> return;
>
> + /* Check for an ERETAx */
> + esr = kvm_vcpu_get_esr(vcpu);
> + if (esr_iss_is_eretax(esr) && !kvm_auth_eretax(vcpu, &elr)) {
> + /*
> + * Oh no, ERETAx failed to authenticate. If we have
> + * FPACCOMBINE, deliver an exception right away. If we
> + * don't, then let the mangled ELR value trickle down the
> + * ERET handling, and the guest will have a little surprise.
> + */
> + if (kvm_has_pauth(vcpu->kvm, FPACCOMBINE)) {
> + esr &= ESR_ELx_ERET_ISS_ERETA;
> + esr |= FIELD_PREP(ESR_ELx_EC_MASK, ESR_ELx_EC_FPAC);
> + kvm_inject_nested_sync(vcpu, esr);
> + return;
> + }
> + }
> +
> preempt_disable();
> kvm_arch_vcpu_put(vcpu);
>
> spsr = __vcpu_sys_reg(vcpu, SPSR_EL2);
> spsr = kvm_check_illegal_exception_return(vcpu, spsr);
> - elr = __vcpu_sys_reg(vcpu, ELR_EL2);
> + if (!esr_iss_is_eretax(esr))
> + elr = __vcpu_sys_reg(vcpu, ELR_EL2);
>
> trace_kvm_nested_eret(vcpu, elr, spsr);
>
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index 1ba2f788b2c3..407bdfbb572b 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -248,7 +248,8 @@ static int kvm_handle_ptrauth(struct kvm_vcpu *vcpu)
>
> static int kvm_handle_eret(struct kvm_vcpu *vcpu)
> {
> - if (esr_iss_is_eretax(kvm_vcpu_get_esr(vcpu)))
> + if (esr_iss_is_eretax(kvm_vcpu_get_esr(vcpu)) &&
> + !vcpu_has_ptrauth(vcpu))
> return kvm_handle_ptrauth(vcpu);
>
> /*
> diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
> index 3ea9bdf6b555..49d36666040e 100644
> --- a/arch/arm64/kvm/hyp/vhe/switch.c
> +++ b/arch/arm64/kvm/hyp/vhe/switch.c
> @@ -208,7 +208,8 @@ void kvm_vcpu_put_vhe(struct kvm_vcpu *vcpu)
>
> static bool kvm_hyp_handle_eret(struct kvm_vcpu *vcpu, u64 *exit_code)
> {
> - u64 spsr, mode;
> + u64 esr = kvm_vcpu_get_esr(vcpu);
> + u64 spsr, elr, mode;
>
> /*
> * Going through the whole put/load motions is a waste of time
> @@ -242,10 +243,18 @@ static bool kvm_hyp_handle_eret(struct kvm_vcpu *vcpu, u64 *exit_code)
> return false;
> }
>
> + /* If ERETAx fails, take the slow path */
> + if (esr_iss_is_eretax(esr)) {
> + if (!(vcpu_has_ptrauth(vcpu) && kvm_auth_eretax(vcpu, &elr)))
> + return false;
> + } else {
> + elr = read_sysreg_el1(SYS_ELR);
> + }
> +
> spsr = (spsr & ~(PSR_MODE_MASK | PSR_MODE32_BIT)) | mode;
>
> write_sysreg_el2(spsr, SYS_SPSR);
> - write_sysreg_el2(read_sysreg_el1(SYS_ELR), SYS_ELR);
> + write_sysreg_el2(elr, SYS_ELR);
>
> return true;
> }
>
Reviewed-by: Joey Gouly <joey.gouly@xxxxxxx>
Thanks,
Joey
