Re: [PATCH 2/2] KVM: arm64: Map hyp text as RO and dump instr on panic

[Ben Horgan <ben.horgan@arm.com>]

Hi Mostafa,

On 18/07/2025 00:47, Mostafa Saleh wrote:
> Map the hyp text section as RO, there are no secrets there
> and that allows the kernel extract info for debugging.
> 
> As in case of panic we can now dump the faulting instructions
> similar to the kernel.
> 
> Signed-off-by: Mostafa Saleh <smostafa@google.com>
> ---
>   arch/arm64/kvm/handle_exit.c    |  4 +---
>   arch/arm64/kvm/hyp/nvhe/setup.c | 12 ++++++++++--
>   2 files changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index de12b4d4bccd..d59f33c40767 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -566,9 +566,7 @@ void __noreturn __cold nvhe_hyp_panic_handler(u64 esr, u64 spsr,
>   	kvm_nvhe_dump_backtrace(hyp_offset);
>   
>   	/* Dump the faulting instruction */
> -	if (!is_protected_kvm_enabled() ||
> -	    IS_ENABLED(CONFIG_NVHE_EL2_DEBUG))
> -		dump_instr(panic_addr + kaslr_offset());
> +	dump_instr(panic_addr + kaslr_offset());
This makes the dumping in nvhe no longer conditional on 
CONFIG_NVHE_EL2_DEBUG. A change from what you introduced in the patch. 
Perhaps it makes sense to reorder the patches; do the preparatory work 
for instruction dumping before the enabling.>
>   	/*
>   	 * Hyp has panicked and we're going to handle that by panicking the
> diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
> index a48d3f5a5afb..90bd014e952f 100644
> --- a/arch/arm64/kvm/hyp/nvhe/setup.c
> +++ b/arch/arm64/kvm/hyp/nvhe/setup.c
> @@ -192,6 +192,7 @@ static int fix_host_ownership_walker(const struct kvm_pgtable_visit_ctx *ctx,
>   	enum pkvm_page_state state;
>   	struct hyp_page *page;
>   	phys_addr_t phys;
> +	enum kvm_pgtable_prot prot;
>   
>   	if (!kvm_pte_valid(ctx->old))
>   		return 0;
> @@ -210,11 +211,18 @@ static int fix_host_ownership_walker(const struct kvm_pgtable_visit_ctx *ctx,
>   	 * configured in the hypervisor stage-1, and make sure to propagate them
>   	 * to the hyp_vmemmap state.
>   	 */
> -	state = pkvm_getstate(kvm_pgtable_hyp_pte_prot(ctx->old));
> +	prot = kvm_pgtable_hyp_pte_prot(ctx->old);
> +	state = pkvm_getstate(prot);
>   	switch (state) {
>   	case PKVM_PAGE_OWNED:
>   		set_hyp_state(page, PKVM_PAGE_OWNED);
> -		return host_stage2_set_owner_locked(phys, PAGE_SIZE, PKVM_ID_HYP);
> +		/* hyp text is RO in the host stage-2 to be inspected on panic. */
> +		if (prot == PAGE_HYP_EXEC) {
> +			set_host_state(page, PKVM_NOPAGE);
> +			return host_stage2_idmap_locked(phys, PAGE_SIZE, KVM_PGTABLE_PROT_R);
> +		} else {
> +			return host_stage2_set_owner_locked(phys, PAGE_SIZE, PKVM_ID_HYP);
> +		}
>   	case PKVM_PAGE_SHARED_OWNED:
>   		set_hyp_state(page, PKVM_PAGE_SHARED_OWNED);
>   		set_host_state(page, PKVM_PAGE_SHARED_BORROWED);
-- 
Thanks,

Ben