On Fri, 08 Apr 2022 21:03:28 +0100,
Kalesh Singh <kaleshsingh@xxxxxxxxxx> wrote:
>
> The hypervisor stacks (for both nVHE Hyp mode and nVHE protected mode)
> are aligned such that any valid stack address has PAGE_SHIFT bit as 1.
> This allows us to conveniently check for overflow in the exception entry
> without corrupting any GPRs. We won't recover from a stack overflow so
> panic the hypervisor.
>
> Signed-off-by: Kalesh Singh <kaleshsingh@xxxxxxxxxx>
> Tested-by: Fuad Tabba <tabba@xxxxxxxxxx>
> Reviewed-by: Fuad Tabba <tabba@xxxxxxxxxx>
> ---
>
> Changes in v7:
> - Add Fuad's Reviewed-by and Tested-by tags.
>
> Changes in v5:
> - Valid stack addresses now have PAGE_SHIFT bit as 1 instead of 0
>
> Changes in v3:
> - Remove test_sp_overflow macro, per Mark
> - Add asmlinkage attribute for hyp_panic, hyp_panic_bad_stack, per Ard
>
>
> arch/arm64/kvm/hyp/nvhe/host.S | 24 ++++++++++++++++++++++++
> arch/arm64/kvm/hyp/nvhe/switch.c | 7 ++++++-
> 2 files changed, 30 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kvm/hyp/nvhe/host.S b/arch/arm64/kvm/hyp/nvhe/host.S
> index 3d613e721a75..be6d844279b1 100644
> --- a/arch/arm64/kvm/hyp/nvhe/host.S
> +++ b/arch/arm64/kvm/hyp/nvhe/host.S
> @@ -153,6 +153,18 @@ SYM_FUNC_END(__host_hvc)
>
> .macro invalid_host_el2_vect
> .align 7
> +
> + /*
> + * Test whether the SP has overflowed, without corrupting a GPR.
> + * nVHE hypervisor stacks are aligned so that the PAGE_SHIFT bit
> + * of SP should always be 1.
> + */
> + add sp, sp, x0 // sp' = sp + x0
> + sub x0, sp, x0 // x0' = sp' - x0 = (sp + x0) - x0 = sp
> + tbz x0, #PAGE_SHIFT, .L__hyp_sp_overflow\@
> + sub x0, sp, x0 // x0'' = sp' - x0' = (sp + x0) - sp = x0
> + sub sp, sp, x0 // sp'' = sp' - x0 = (sp + x0) - x0 = sp
> +
> /* If a guest is loaded, panic out of it. */
> stp x0, x1, [sp, #-16]!
> get_loaded_vcpu x0, x1
> @@ -165,6 +177,18 @@ SYM_FUNC_END(__host_hvc)
> * been partially clobbered by __host_enter.
> */
> b hyp_panic
> +
> +.L__hyp_sp_overflow\@:
> + /*
> + * Reset SP to the top of the stack, to allow handling the hyp_panic.
> + * This corrupts the stack but is ok, since we won't be attempting
> + * any unwinding here.
> + */
> + ldr_this_cpu x0, kvm_init_params + NVHE_INIT_STACK_HYP_VA, x1
> + mov sp, x0
> +
> + bl hyp_panic_bad_stack
Why bl? You clearly don't expect to return here, given that you have
an ASM_BUG() right below, and that you are calling a __no_return
function. I think we should be consistent with the rest of the code
and just do a simple branch.
It also gives us a chance to preserve an extra register from the
context.
> + ASM_BUG()
> .endm
>
> .macro invalid_host_el1_vect
> diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c
> index 6410d21d8695..703a5d3f611b 100644
> --- a/arch/arm64/kvm/hyp/nvhe/switch.c
> +++ b/arch/arm64/kvm/hyp/nvhe/switch.c
> @@ -347,7 +347,7 @@ int __kvm_vcpu_run(struct kvm_vcpu *vcpu)
> return exit_code;
> }
>
> -void __noreturn hyp_panic(void)
> +asmlinkage void __noreturn hyp_panic(void)
> {
> u64 spsr = read_sysreg_el2(SYS_SPSR);
> u64 elr = read_sysreg_el2(SYS_ELR);
> @@ -369,6 +369,11 @@ void __noreturn hyp_panic(void)
> unreachable();
> }
>
> +asmlinkage void __noreturn hyp_panic_bad_stack(void)
> +{
> + hyp_panic();
> +}
> +
> asmlinkage void kvm_unexpected_el2_exception(void)
> {
> return __kvm_unexpected_el2_exception();
> --
> 2.35.1.1178.g4f1659d476-goog
>
>
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
_______________________________________________
kvmarm mailing list
kvmarm@xxxxxxxxxxxxxxxxxxxxx
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
