[PATCH 4.4 49/92] powerpc/mm: Make NULL pointer deferences explicit on bad page faults.

Greg Kroah-Hartman
2019-12-04T18:25:44Z

From: Christophe Leroy <christophe.leroy@c-s.fr>

[ 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>
---
arch/powerpc/mm/fault.c | 17 +++++++++--------
1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index d154e333f76b7..d1f860ca03ade 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -521,21 +521,22 @@ 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",
--
2.20.1