[PATCH] powerpc/32: Implement validation of emergency stack

[Christophe Leroy]

VMAP stack added an emergency stack on powerpc/32 for when there is
a stack overflow, but failed to add stack validation for that
emergency stack. That validation is required for show stack.

Implement it.

Signed-off-by: Christophe Leroy <christophe.le...@csgroup.eu>
---
 arch/powerpc/include/asm/thread_info.h |  4 ++++
 arch/powerpc/kernel/process.c          | 20 ++++++++++++++++++--
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/thread_info.h 
b/arch/powerpc/include/asm/thread_info.h
index 15c5691dd218..d2f356e57387 100644
--- a/arch/powerpc/include/asm/thread_info.h
+++ b/arch/powerpc/include/asm/thread_info.h
@@ -226,6 +226,10 @@ static inline int arch_within_stack_frames(const void * 
const stack,
        return BAD_STACK;
 }
 
+#ifdef CONFIG_VMAP_STACK
+extern void *emergency_ctx[];
+#endif
+
 #endif /* !__ASSEMBLY__ */
 
 #endif /* __KERNEL__ */
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 3b506d4c55f3..b27e2f69930c 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -2177,10 +2177,10 @@ static inline int valid_irq_stack(unsigned long sp, 
struct task_struct *p,
        return 0;
 }
 
+#ifdef CONFIG_PPC64
 static inline int valid_emergency_stack(unsigned long sp, struct task_struct 
*p,
                                        unsigned long nbytes)
 {
-#ifdef CONFIG_PPC64
        unsigned long stack_page;
        unsigned long cpu = task_cpu(p);
 
@@ -2208,10 +2208,26 @@ static inline int valid_emergency_stack(unsigned long 
sp, struct task_struct *p,
        if (sp >= stack_page && sp <= stack_page + THREAD_SIZE - nbytes)
                return 1;
 # endif
-#endif
 
        return 0;
 }
+#else
+static inline int valid_emergency_stack(unsigned long sp, struct task_struct 
*p,
+                                       unsigned long nbytes)
+{
+       unsigned long stack_page;
+       unsigned long cpu = task_cpu(p);
+
+       if (!IS_ENABLED(CONFIG_VMAP_STACK))
+               return 0;
+
+       stack_page = (unsigned long)emergency_ctx[cpu] - THREAD_SIZE;
+       if (sp >= stack_page && sp <= stack_page + THREAD_SIZE - nbytes)
+               return 1;
+
+       return 0;
+}
+#endif
 
 /*
  * validate the stack frame of a particular minimum size, used for when we are
-- 
2.44.0