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

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Message-ID: <20250717234744.2254371-3-smostafa@google.com>
Date: Thu, 17 Jul 2025 23:47:44 +0000
From: Mostafa Saleh <smostafa@...gle.com>
To: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	kvmarm@...ts.linux.dev
Cc: catalin.marinas@....com, will@...nel.org, maz@...nel.org, 
	oliver.upton@...ux.dev, joey.gouly@....com, suzuki.poulose@....com, 
	yuzenghui@...wei.com, qperret@...gle.com, keirf@...gle.com, 
	Mostafa Saleh <smostafa@...gle.com>
Subject: [PATCH 2/2] KVM: arm64: Map hyp text as RO and dump instr on panic

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@...gle.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());
 
 	/*
 	 * 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);
-- 
2.50.0.727.gbf7dc18ff4-goog