parisc: Avoid crash due to unaligned access in unwinder

Guenter Roeck reported this kernel crash on his emulated B160L machine:

Starting network: udhcpc: started, v1.36.1
 Backtrace:
  [<104320d4>] unwind_once+0x1c/0x5c
  [<10434a00>] walk_stackframe.isra.0+0x74/0xb8
  [<10434a6c>] arch_stack_walk+0x28/0x38
  [<104e5efc>] stack_trace_save+0x48/0x5c
  [<105d1bdc>] set_track_prepare+0x44/0x6c
  [<105d9c80>] ___slab_alloc+0xfc4/0x1024
  [<105d9d38>] __slab_alloc.isra.0+0x58/0x90
  [<105dc80c>] kmem_cache_alloc_noprof+0x2ac/0x4a0
  [<105b8e54>] __anon_vma_prepare+0x60/0x280
  [<105a823c>] __vmf_anon_prepare+0x68/0x94
  [<105a8b34>] do_wp_page+0x8cc/0xf10
  [<105aad88>] handle_mm_fault+0x6c0/0xf08
  [<10425568>] do_page_fault+0x110/0x440
  [<10427938>] handle_interruption+0x184/0x748
  [<11178398>] schedule+0x4c/0x190
  BUG: spinlock recursion on CPU#0, ifconfig/2420
  lock: terminate_lock.2+0x0/0x1c, .magic: dead4ead, .owner: ifconfig/2420, .owner_cpu: 0

While creating the stack trace, the unwinder uses the stack pointer to guess
the previous frame to read the previous stack pointer from memory.  The crash
happens, because the unwinder tries to read from unaligned memory and as such
triggers the unalignment trap handler which then leads to the spinlock
recursion and finally to a deadlock.

Fix it by checking the alignment before accessing the memory.

Reported-by: Guenter Roeck <[email protected]>
Signed-off-by: Helge Deller <[email protected]>
Tested-by: Guenter Roeck <[email protected]>
Cc: [email protected] # v6.12+

Author: hdeller

arch/parisc/kernel/unwind.c

@@ -35,6 +35,8 @@
 
 #define KERNEL_START (KERNEL_BINARY_TEXT_START)
 
+#define ALIGNMENT_OK(ptr, type) (((ptr) & (sizeof(type) - 1)) == 0)
+
 extern struct unwind_table_entry __start___unwind[];
 extern struct unwind_table_entry __stop___unwind[];
 
@@ -257,12 +259,15 @@ static int unwind_special(struct unwind_frame_info *info, unsigned long pc, int
 	if (pc_is_kernel_fn(pc, _switch_to) ||
 	    pc == (unsigned long)&_switch_to_ret) {
 		info->prev_sp = info->sp - CALLEE_SAVE_FRAME_SIZE;
-		info->prev_ip = *(unsigned long *)(info->prev_sp - RP_OFFSET);
+		if (ALIGNMENT_OK(info->prev_sp, long))
+			info->prev_ip = *(unsigned long *)(info->prev_sp - RP_OFFSET);
+		else
+			info->prev_ip = info->prev_sp = 0;
 		return 1;
 	}
 
 #ifdef CONFIG_IRQSTACKS
-	if (pc == (unsigned long)&_call_on_stack) {
+	if (pc == (unsigned long)&_call_on_stack && ALIGNMENT_OK(info->sp, long)) {
 		info->prev_sp = *(unsigned long *)(info->sp - FRAME_SIZE - REG_SZ);
 		info->prev_ip = *(unsigned long *)(info->sp - FRAME_SIZE - RP_OFFSET);
 		return 1;
@@ -370,8 +375,10 @@ static void unwind_frame_regs(struct unwind_frame_info *info)
 			info->prev_sp = info->sp - frame_size;
 			if (e->Millicode)
 				info->rp = info->r31;
-			else if (rpoffset)
+			else if (rpoffset && ALIGNMENT_OK(info->prev_sp, long))
 				info->rp = *(unsigned long *)(info->prev_sp - rpoffset);
+			else
+				info->rp = 0;
 			info->prev_ip = info->rp;
 			info->rp = 0;
 		}