ANDROID: 16K: Fix show maps CFI failure

If the kernel is built CONFIG_CFI_CLANG=y, reading smaps
may cause a panic. This is due to a failed CFI check; which
is triggered becuase the signature of the function pointer for
printing smaps padding VMAs does not match exactly with that
for show_smap().

Fix this by casting the function pointer to the expected type
based on whether printing maps or smaps padding.

Bug: 383389169
Bug: 330117029
Bug: 327600007
Bug: 330767927
Bug: 328266487
Bug: 329803029
Change-Id: I65564a547dacbc4131f8557344c8c96e51f90cd5
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>

fs/proc/task_mmu.c

@@ -372,7 +372,7 @@ static int show_map(struct seq_file *m, void *v)
 	if (vma_pages(vma))
 		show_map_vma(m, vma);
 
-	show_map_pad_vma(vma, pad_vma, m, show_map_vma);
+	show_map_pad_vma(vma, pad_vma, m, show_map_vma, false);
 
 	return 0;
 }
@@ -1186,7 +1186,7 @@ static int show_smap(struct seq_file *m, void *v)
 	show_smap_vma_flags(m, vma);
 
 show_pad:
-	show_map_pad_vma(vma, pad_vma, m, (show_pad_vma_fn)((void*)show_smap));
+	show_map_pad_vma(vma, pad_vma, m, show_smap, true);
 
 	return 0;
 }

include/linux/pgsize_migration.h

@@ -43,8 +43,6 @@
 #define VM_PAD_MASK		(VM_TOTAL_PAD_PAGES << VM_PAD_SHIFT)
 #define VMA_PAD_START(vma)	(vma->vm_end - (vma_pad_pages(vma) << PAGE_SHIFT))
 
-typedef void (*show_pad_vma_fn)(struct seq_file *m, struct vm_area_struct *vma);
-
 #if PAGE_SIZE == SZ_4K && defined(CONFIG_64BIT)
 extern void vma_set_pad_pages(struct vm_area_struct *vma,
 			      unsigned long nr_pages);
@@ -60,7 +58,7 @@ extern struct vm_area_struct *get_data_vma(struct vm_area_struct *vma);
 
 extern void show_map_pad_vma(struct vm_area_struct *vma,
 			     struct vm_area_struct *pad,
-			     struct seq_file *m, show_pad_vma_fn func);
+			     struct seq_file *m, void *func, bool smaps);
 
 extern void split_pad_vma(struct vm_area_struct *vma, struct vm_area_struct *new,
 			  unsigned long addr, int new_below);
@@ -92,7 +90,7 @@ static inline struct vm_area_struct *get_data_vma(struct vm_area_struct *vma)
 
 static inline void show_map_pad_vma(struct vm_area_struct *vma,
 				    struct vm_area_struct *pad,
-				    struct seq_file *m, show_pad_vma_fn func)
+				    struct seq_file *m, void *func, bool smaps)
 {
 }
 

mm/pgsize_migration.c

@@ -20,6 +20,9 @@
 #include <linux/slab.h>
 #include <linux/sysfs.h>
 
+typedef void (*show_pad_maps_fn)	(struct seq_file *m, struct vm_area_struct *vma);
+typedef int  (*show_pad_smaps_fn)	(struct seq_file *m, void *v);
+
 #ifdef CONFIG_64BIT
 #if PAGE_SIZE == SZ_4K
 DEFINE_STATIC_KEY_TRUE(pgsize_migration_enabled);
@@ -303,7 +306,7 @@ struct vm_area_struct *get_data_vma(struct vm_area_struct *vma)
  * and @pad.
  */
 void show_map_pad_vma(struct vm_area_struct *vma, struct vm_area_struct *pad,
-		      struct seq_file *m, show_pad_vma_fn func)
+		      struct seq_file *m, void *func, bool smaps)
 {
 	if (!pad)
 		return;
@@ -320,7 +323,10 @@ void show_map_pad_vma(struct vm_area_struct *vma, struct vm_area_struct *pad,
 	 */
 	BUG_ON(!vma);
 
-	func(m, pad);
+	if (smaps)
+		((show_pad_smaps_fn)func)(m, pad);
+	else
+		((show_pad_maps_fn)func)(m, pad);
 
 	kfree(pad);
 	kfree(vma);