[PATCH v3 3/8] KVM: arm64: Add guard pages for KVM nVHE hypervisor stack

[Kalesh Singh <kaleshsingh@google.com>]

Maps the stack pages in the flexible private VA range and allocates
guard pages below the stack as unbacked VA space. The stack is aligned
to twice its size to aid overflow detection (implemented in a subsequent
patch in the series).

Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
---

Changes in v3:
  - Handle null ptr in IS_ERR_OR_NULL checks, per Mark

 arch/arm64/include/asm/kvm_asm.h |  1 +
 arch/arm64/kvm/arm.c             | 32 +++++++++++++++++++++++++++++---
 2 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index d5b0386ef765..2e277f2ed671 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -169,6 +169,7 @@ struct kvm_nvhe_init_params {
 	unsigned long tcr_el2;
 	unsigned long tpidr_el2;
 	unsigned long stack_hyp_va;
+	unsigned long stack_pa;
 	phys_addr_t pgd_pa;
 	unsigned long hcr_el2;
 	unsigned long vttbr;
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index ecc5958e27fe..7a23630c4a7f 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1541,7 +1541,6 @@ static void cpu_prepare_hyp_mode(int cpu)
 	tcr |= (idmap_t0sz & GENMASK(TCR_TxSZ_WIDTH - 1, 0)) << TCR_T0SZ_OFFSET;
 	params->tcr_el2 = tcr;
 
-	params->stack_hyp_va = kern_hyp_va(per_cpu(kvm_arm_hyp_stack_page, cpu) + PAGE_SIZE);
 	params->pgd_pa = kvm_mmu_get_httbr();
 	if (is_protected_kvm_enabled())
 		params->hcr_el2 = HCR_HOST_NVHE_PROTECTED_FLAGS;
@@ -1990,14 +1989,41 @@ static int init_hyp_mode(void)
 	 * Map the Hyp stack pages
 	 */
 	for_each_possible_cpu(cpu) {
+		struct kvm_nvhe_init_params *params = per_cpu_ptr_nvhe_sym(kvm_init_params, cpu);
 		char *stack_page = (char *)per_cpu(kvm_arm_hyp_stack_page, cpu);
-		err = create_hyp_mappings(stack_page, stack_page + PAGE_SIZE,
-					  PAGE_HYP);
+		unsigned long stack_hyp_va, guard_hyp_va;
 
+		/*
+		 * Private mappings are allocated downwards from io_map_base
+		 * so allocate the stack first then the guard page.
+		 *
+		 * The stack is aligned to twice its size to facilitate overflow
+		 * detection.
+		 */
+		err = __create_hyp_private_mapping(__pa(stack_page), PAGE_SIZE,
+						PAGE_SIZE * 2, &stack_hyp_va, PAGE_HYP);
 		if (err) {
 			kvm_err("Cannot map hyp stack\n");
 			goto out_err;
 		}
+
+		/* Allocate unbacked private VA range for stack guard page */
+		guard_hyp_va = hyp_alloc_private_va_range(PAGE_SIZE, PAGE_SIZE);
+		if (IS_ERR_OR_NULL((void *)guard_hyp_va)) {
+			err = guard_hyp_va ? PTR_ERR((void *)guard_hyp_va) : -ENOMEM;
+			kvm_err("Cannot allocate hyp stack guard page\n");
+			goto out_err;
+		}
+
+		/*
+		 * Save the stack PA in nvhe_init_params. This will be needed to recreate
+		 * the stack mapping in protected nVHE mode. __hyp_pa() won't do the right
+		 * thing there, since the stack has been mapped in the flexible private
+		 * VA space.
+		 */
+		params->stack_pa = __pa(stack_page) + PAGE_SIZE;
+
+		params->stack_hyp_va = stack_hyp_va + PAGE_SIZE;
 	}
 
 	for_each_possible_cpu(cpu) {
-- 
2.35.1.473.g83b2b277ed-goog