[PATCH v2 4/9] KVM: arm64: Add guard pages for pKVM (protected nVHE) hypervisor stack

[Kalesh Singh]

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 at google.com>
---
 arch/arm64/kvm/hyp/nvhe/setup.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
index 27af337f9fea..69df21320b09 100644
--- a/arch/arm64/kvm/hyp/nvhe/setup.c
+++ b/arch/arm64/kvm/hyp/nvhe/setup.c
@@ -105,11 +105,28 @@ static int recreate_hyp_mappings(phys_addr_t phys, unsigned long size,
 		if (ret)
 			return ret;
 
-		end = (void *)per_cpu_ptr(&kvm_init_params, i)->stack_hyp_va;
+		/*
+		 * Private mappings are allocated upwards from __io_map_base
+		 * so allocate the guard page first then the stack.
+		 */
+		start = (void *)pkvm_alloc_private_va_range(PAGE_SIZE, PAGE_SIZE);
+		if (IS_ERR_OR_NULL(start))
+			return PTR_ERR(start);
+
+		/*
+		 * The stack is aligned to twice its size to facilitate overflow
+		 * detection.
+		 */
+		end = (void *)per_cpu_ptr(&kvm_init_params, i)->stack_pa;
 		start = end - PAGE_SIZE;
-		ret = pkvm_create_mappings(start, end, PAGE_HYP);
-		if (ret)
-			return ret;
+		start = (void *)__pkvm_create_private_mapping((phys_addr_t)start,
+					PAGE_SIZE, PAGE_SIZE * 2, PAGE_HYP);
+		if (IS_ERR_OR_NULL(start))
+			return PTR_ERR(start);
+		end = start + PAGE_SIZE;
+
+		/* Update stack_hyp_va to end of the stack's private VA range */
+		per_cpu_ptr(&kvm_init_params, i)->stack_hyp_va = (unsigned long) end;
 	}
 
 	/*
-- 
2.35.1.473.g83b2b277ed-goog