powerpc/mm: Make NULL pointer deferences explicit on bad page faults.

[ Upstream commit 49a502ea23bf9dec47f8f3c3960909ff409cd1bb ]

As several other arches including x86, this patch makes it explicit
that a bad page fault is a NULL pointer dereference when the fault
address is lower than PAGE_SIZE

In the mean time, this page makes all bad_page_fault() messages
shorter so that they remain on one single line. And it prefixes them
by "BUG: " so that they get easily grepped.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
[mpe: Avoid pr_cont()]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 52863deed65df8a16dd272279aaeff9c19ee0081..5fc8a010fdf07a0bda29ad8a1c2ad1ccba4318f8 100644 (file)
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -581,21 +581,22 @@ void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
        switch (regs->trap) {
        case 0x300:
        case 0x380:
-               printk(KERN_ALERT "Unable to handle kernel paging request for "
-                       "data at address 0x%08lx\n", regs->dar);
+               pr_alert("BUG: %s at 0x%08lx\n",
+                        regs->dar < PAGE_SIZE ? "Kernel NULL pointer dereference" :
+                        "Unable to handle kernel data access", regs->dar);
                break;
        case 0x400:
        case 0x480:
-               printk(KERN_ALERT "Unable to handle kernel paging request for "
-                       "instruction fetch\n");
+               pr_alert("BUG: Unable to handle kernel instruction fetch%s",
+                        regs->nip < PAGE_SIZE ? " (NULL pointer?)\n" : "\n");
                break;
        case 0x600:
-               printk(KERN_ALERT "Unable to handle kernel paging request for "
-                       "unaligned access at address 0x%08lx\n", regs->dar);
+               pr_alert("BUG: Unable to handle kernel unaligned access at 0x%08lx\n",
+                        regs->dar);
                break;
        default:
-               printk(KERN_ALERT "Unable to handle kernel paging request for "
-                       "unknown fault\n");
+               pr_alert("BUG: Unable to handle unknown paging fault at 0x%08lx\n",
+                        regs->dar);
                break;
        }
        printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",