[PATCH 4/4] powerpc: Skip stack validation checking alternate stacks if they are not allocated

[Nicholas Piggin <npiggin@gmail.com>]

Stack validation in early boot can just bail out of checking alternate
stacks if they are not validated yet. Checking against a NULL stack
could cause NULLish pointer values to be considered valid.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/kernel/process.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index edb46d0806ef..95d605bdff85 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -2118,6 +2118,9 @@ static inline int valid_irq_stack(unsigned long sp, struct task_struct *p,
 	unsigned long stack_page;
 	unsigned long cpu = task_cpu(p);
 
+	if (!hardirq_ctx[cpu] || !softirq_ctx[cpu])
+		return 0;
+
 	stack_page = (unsigned long)hardirq_ctx[cpu];
 	if (sp >= stack_page && sp <= stack_page + THREAD_SIZE - nbytes)
 		return 1;
@@ -2139,6 +2142,14 @@ static inline int valid_emergency_stack(unsigned long sp, struct task_struct *p,
 	if (!paca_ptrs)
 		return 0;
 
+	if (!paca_ptrs[cpu]->emergency_sp)
+		return 0;
+
+# ifdef CONFIG_PPC_BOOK3S_64
+	if (!paca_ptrs[cpu]->nmi_emergency_sp || !paca_ptrs[cpu]->mc_emergency_sp)
+		return 0;
+#endif
+
 	stack_page = (unsigned long)paca_ptrs[cpu]->emergency_sp - THREAD_SIZE;
 	if (sp >= stack_page && sp <= stack_page + THREAD_SIZE - nbytes)
 		return 1;
-- 
2.37.2