Re: [PATCH v5 14/17] KVM: arm64: Implement protected nVHE hyp stack unwinder

Fuad Tabba
2022-07-21T09:59:35Z

Hi Kalesh,

On Thu, Jul 21, 2022 at 6:58 AM Kalesh Singh <kaleshsingh@google.com> wrote:
>
> Implements the common framework necessary for unwind() to work in
> the protected nVHE context:
> - on_accessible_stack()
> - on_overflow_stack()
> - unwind_next()
>
> Protected nVHE unwind() is used to unwind and save the hyp stack
> addresses to the shared stacktrace buffer. The host reads the
> entries in this buffer, symbolizes and dumps the stacktrace (later
> patch in the series).
>
> Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
> ---

Reviewed-by: Fuad Tabba <tabba@google.com>

Cheers,
/fuad

> arch/arm64/include/asm/stacktrace/common.h | 2 ++
> arch/arm64/include/asm/stacktrace/nvhe.h | 34 ++++++++++++++++++++--
> 2 files changed, 34 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/include/asm/stacktrace/common.h b/arch/arm64/include/asm/stacktrace/common.h
> index be7920ba70b0..73fd9e143c4a 100644
> --- a/arch/arm64/include/asm/stacktrace/common.h
> +++ b/arch/arm64/include/asm/stacktrace/common.h
> @@ -34,6 +34,7 @@ enum stack_type {
> STACK_TYPE_OVERFLOW,
> STACK_TYPE_SDEI_NORMAL,
> STACK_TYPE_SDEI_CRITICAL,
> + STACK_TYPE_HYP,
> __NR_STACK_TYPES
> };
>
> @@ -186,6 +187,7 @@ static inline int unwind_next_common(struct unwind_state *state,
> *
> * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
> * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
> + * HYP -> OVERFLOW
> *
> * ... but the nesting itself is strict. Once we transition from one
> * stack to another, it's never valid to unwind back to that first
> diff --git a/arch/arm64/include/asm/stacktrace/nvhe.h b/arch/arm64/include/asm/stacktrace/nvhe.h
> index 8f02803a005f..c3688e717136 100644
> --- a/arch/arm64/include/asm/stacktrace/nvhe.h
> +++ b/arch/arm64/include/asm/stacktrace/nvhe.h
> @@ -39,10 +39,19 @@ static inline void kvm_nvhe_unwind_init(struct unwind_state *state,
> state->pc = pc;
> }
>
> +static inline bool on_hyp_stack(unsigned long sp, unsigned long size,
> + struct stack_info *info);
> +
> static inline bool on_accessible_stack(const struct task_struct *tsk,
> unsigned long sp, unsigned long size,
> struct stack_info *info)
> {
> + if (on_accessible_stack_common(tsk, sp, size, info))
> + return true;
> +
> + if (on_hyp_stack(sp, size, info))
> + return true;
> +
> return false;
> }
>
> @@ -60,12 +69,27 @@ DECLARE_PER_CPU(struct kvm_nvhe_init_params, kvm_init_params);
> static inline bool on_overflow_stack(unsigned long sp, unsigned long size,
> struct stack_info *info)
> {
> - return false;
> + unsigned long low = (unsigned long)this_cpu_ptr(overflow_stack);
> + unsigned long high = low + OVERFLOW_STACK_SIZE;
> +
> + return on_stack(sp, size, low, high, STACK_TYPE_OVERFLOW, info);
> +}
> +
> +static inline bool on_hyp_stack(unsigned long sp, unsigned long size,
> + struct stack_info *info)
> +{
> + struct kvm_nvhe_init_params *params = this_cpu_ptr(&kvm_init_params);
> + unsigned long high = params->stack_hyp_va;
> + unsigned long low = high - PAGE_SIZE;
> +
> + return on_stack(sp, size, low, high, STACK_TYPE_HYP, info);
> }
>
> static inline int notrace unwind_next(struct unwind_state *state)
> {
> - return 0;
> + struct stack_info info;
> +
> + return unwind_next_common(state, &info, NULL);
> }
> NOKPROBE_SYMBOL(unwind_next);
> #else /* !CONFIG_PROTECTED_NVHE_STACKTRACE */
> @@ -75,6 +99,12 @@ static inline bool on_overflow_stack(unsigned long sp, unsigned long size,
> return false;
> }
>
> +static inline bool on_hyp_stack(unsigned long sp, unsigned long size,
> + struct stack_info *info)
> +{
> + return false;
> +}
> +
> static inline int notrace unwind_next(struct unwind_state *state)
> {
> return 0;
> --
> 2.37.0.170.g444d1eabd0-goog
>