Re: [PATCH v2 4/9] arm64: KVM: Make unexpected reads from WO registers inject an undef

Christoffer Dall
2017-03-28T12:43:20Z

On Mon, Mar 27, 2017 at 05:03:40PM +0100, Marc Zyngier wrote:
> Reads from write-only system registers are generally confined to
> EL1 and not propagated to EL2 (that's what the architecture
> mantates). In order to be sure that we have a sane behaviour
> even in the unlikely event that we have a broken system, we still
> handle it in KVM.
>
> In that case, let's inject an undef into the guest.
>
> Let's also remove write_to_read_only which isn't used anywhere.
>

Reviewed-by: Christoffer Dall <cdall@linaro.org>

> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
> arch/arm64/kvm/sys_regs.c | 9 +++++++++
> arch/arm64/kvm/sys_regs.h | 18 ------------------
> 2 files changed, 9 insertions(+), 18 deletions(-)
>
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 5e3ce7890b35..19a036b4f6ac 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -55,6 +55,15 @@
> * 64bit interface.
> */
>
> +static bool read_from_write_only(struct kvm_vcpu *vcpu,
> + const struct sys_reg_params *params)
> +{
> + WARN_ONCE(1, "Unexpected sys_reg read to write-only register\n");
> + print_sys_reg_instr(params);
> + kvm_inject_undefined(vcpu);
> + return false;
> +}
> +
> /* 3 bits per cache level, as per CLIDR, but non-existent caches always 0 */
> static u32 cache_levels;
>
> diff --git a/arch/arm64/kvm/sys_regs.h b/arch/arm64/kvm/sys_regs.h
> index 9c6ffd0f0196..638f724e45af 100644
> --- a/arch/arm64/kvm/sys_regs.h
> +++ b/arch/arm64/kvm/sys_regs.h
> @@ -83,24 +83,6 @@ static inline bool read_zero(struct kvm_vcpu *vcpu,
> return true;
> }
>
> -static inline bool write_to_read_only(struct kvm_vcpu *vcpu,
> - const struct sys_reg_params *params)
> -{
> - kvm_debug("sys_reg write to read-only register at: %lx\n",
> - *vcpu_pc(vcpu));
> - print_sys_reg_instr(params);
> - return false;
> -}
> -
> -static inline bool read_from_write_only(struct kvm_vcpu *vcpu,
> - const struct sys_reg_params *params)
> -{
> - kvm_debug("sys_reg read to write-only register at: %lx\n",
> - *vcpu_pc(vcpu));
> - print_sys_reg_instr(params);
> - return false;
> -}
> -
> /* Reset functions */
> static inline void reset_unknown(struct kvm_vcpu *vcpu,
> const struct sys_reg_desc *r)
> --
> 2.11.0
>