[PATCH 15/21] arm64: KVM: Add panic handling

[Ard Biesheuvel]

On 16 November 2015 at 14:11, Marc Zyngier <marc.zyngier at arm.com> wrote:
> Add the panic handler, together with the small bits of assembly
> code to call the kernel's panic implementation.
>
> Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
> ---
>  arch/arm64/kvm/hyp/hyp-entry.S | 11 ++++++++++-
>  arch/arm64/kvm/hyp/hyp.h       |  1 +
>  arch/arm64/kvm/hyp/switch.c    | 35 +++++++++++++++++++++++++++++++++++
>  3 files changed, 46 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
> index e11a129..7218eed 100644
> --- a/arch/arm64/kvm/hyp/hyp-entry.S
> +++ b/arch/arm64/kvm/hyp/hyp-entry.S
> @@ -141,7 +141,16 @@ el1_irq:
>         mov     x1, #ARM_EXCEPTION_IRQ
>         b       __guest_exit
>
> -.macro invalid_vector  label, target = __kvm_hyp_panic
> +ENTRY(__hyp_do_panic)
> +       mov     lr, #(PSR_F_BIT | PSR_I_BIT | PSR_A_BIT | PSR_D_BIT |\
> +                     PSR_MODE_EL1h)
> +       msr     spsr_el2, lr
> +       ldr     lr, =panic
> +       msr     elr_el2, lr
> +       eret
> +ENDPROC(__hyp_do_panic)
> +
> +.macro invalid_vector  label, target = __hyp_panic
>         .align  2
>  \label:
>         b \target
> diff --git a/arch/arm64/kvm/hyp/hyp.h b/arch/arm64/kvm/hyp/hyp.h
> index 240fb79..d5d500d 100644
> --- a/arch/arm64/kvm/hyp/hyp.h
> +++ b/arch/arm64/kvm/hyp/hyp.h
> @@ -74,6 +74,7 @@ void __fpsimd_save_state(struct user_fpsimd_state *fp_regs);
>  void __fpsimd_restore_state(struct user_fpsimd_state *fp_regs);
>
>  u64 __guest_enter(struct kvm_vcpu *vcpu, struct kvm_cpu_context *host_ctxt);
> +void __noreturn __hyp_do_panic(unsigned long, ...);
>
>  #endif /* __ARM64_KVM_HYP_H__ */
>
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index 06d3e20..cdc2a96 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -140,3 +140,38 @@ int __hyp_text __guest_run(struct kvm_vcpu *vcpu)
>
>         return exit_code;
>  }
> +
> +static const char *__hyp_panic_string = "HYP panic:\nPS:%08x PC:%p ESR:%p\nFAR:%p HPFAR:%p PAR:%p\nVCPU:%p\n";
> +

Re separating the HYP text from the kernel proper: this is exactly the
thing that is likely to cause trouble when you execute the kernel text
from HYP.

__hyp_panic_string is a non-const char pointer containing the absolute
address of the string in the initializer, as seen from the high kernel
virtual mapping.
Better use 'static const char __hyp_panic_string[]' instead.

(If it currenty works fine, it is only because the compiler optimizes
the entire variable away, and performs a relative access in the place
where the variable is referenced.)


> +void __hyp_text __noreturn __hyp_panic(void)
> +{
> +       u64 spsr = read_sysreg(spsr_el2);
> +       u64 elr = read_sysreg(elr_el2);
> +       u64 par = read_sysreg(par_el1);
> +
> +       if (read_sysreg(vttbr_el2)) {
> +               struct kvm_vcpu *vcpu;
> +               struct kvm_cpu_context *host_ctxt;
> +
> +               vcpu = (struct kvm_vcpu *)read_sysreg(tpidr_el2);
> +               host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context);
> +               __deactivate_traps(vcpu);
> +               __deactivate_vm(vcpu);
> +               __sysreg_restore_state(host_ctxt);
> +
> +               write_sysreg(host_ctxt->gp_regs.sp_el1, sp_el1);
> +       }
> +
> +       /* Call panic for real */
> +       while (1) {
> +               unsigned long str_va = (unsigned long)__hyp_panic_string;
> +
> +               str_va -= HYP_PAGE_OFFSET;
> +               str_va += PAGE_OFFSET;
> +               __hyp_do_panic(str_va,
> +                              spsr,  elr,
> +                              read_sysreg(esr_el2),   read_sysreg(far_el2),
> +                              read_sysreg(hpfar_el2), par,
> +                              read_sysreg(tpidr_el2));
> +       }
> +}
> --
> 2.1.4
>
>
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