[PATCH v3] powerpc/kprobes: Ignore traps that happened in real mode

[Christophe Leroy]

When a program check exception happens while MMU translation is
disabled, following Oops happens in kprobe_handler() in the following
code:

		} else if (*addr != BREAKPOINT_INSTRUCTION) {

[   33.098554] BUG: Unable to handle kernel data access on read at 0x0000e268
[   33.105091] Faulting instruction address: 0xc000ec34
[   33.110010] Oops: Kernel access of bad area, sig: 11 [#1]
[   33.115348] BE PAGE_SIZE=16K PREEMPT CMPC885
[   33.119540] Modules linked in:
[   33.122591] CPU: 0 PID: 429 Comm: cat Not tainted 5.6.0-rc1-s3k-dev-00824-g84195dc6c58a #3267
[   33.131005] NIP:  c000ec34 LR: c000ecd8 CTR: c019cab8
[   33.136002] REGS: ca4d3b58 TRAP: 0300   Not tainted  (5.6.0-rc1-s3k-dev-00824-g84195dc6c58a)
[   33.144324] MSR:  00001032 <ME,IR,DR,RI>  CR: 2a4d3c52  XER: 00000000
[   33.150699] DAR: 0000e268 DSISR: c0000000
[   33.150699] GPR00: c000b09c ca4d3c10 c66d0620 00000000 ca4d3c60 00000000 00009032 00000000
[   33.150699] GPR08: 00020000 00000000 c087de44 c000afe0 c66d0ad0 100d3dd6 fffffff3 00000000
[   33.150699] GPR16: 00000000 00000041 00000000 ca4d3d70 00000000 00000000 0000416d 00000000
[   33.150699] GPR24: 00000004 c53b6128 00000000 0000e268 00000000 c07c0000 c07bb6fc ca4d3c60
[   33.188015] NIP [c000ec34] kprobe_handler+0x128/0x290
[   33.192989] LR [c000ecd8] kprobe_handler+0x1cc/0x290
[   33.197854] Call Trace:
[   33.200340] [ca4d3c30] [c000b09c] program_check_exception+0xbc/0x6fc
[   33.206590] [ca4d3c50] [c000e43c] ret_from_except_full+0x0/0x4
[   33.212392] --- interrupt: 700 at 0xe268
[   33.270401] Instruction dump:
[   33.273335] 913e0008 81220000 38600001 3929ffff 91220000 80010024 bb410008 7c0803a6
[   33.280992] 38210020 4e800020 38600000 4e800020 <813b0000> 6d2a7fe0 2f8a0008 419e0154
[   33.288841] ---[ end trace 5b9152d4cdadd06d ]---

kprobe is not prepared to handle events in real mode and functions
running in real mode should have been blacklisted, so kprobe_handler()
can safely bail out telling 'this trap is not mine' for any trap that
happened while in real-mode.

If the trap happened with MSR_IR or MSR_DR cleared, return 0 immediately.

Reported-by: Larry Finger <Larry.Finger at lwfinger.net>
Fixes: 6cc89bad60a6 ("powerpc/kprobes: Invoke handlers directly")
Cc: stable at vger.kernel.org
Cc: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>
Cc: Masami Hiramatsu <mhiramat at kernel.org>
Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>

---
v3: Also bail out if MSR_DR is cleared.

Resending v2 with a more appropriate name

v2: bailing out instead of converting real-time address to virtual and continuing.

The bug might have existed even before that commit from Naveen.

Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>
---
 arch/powerpc/kernel/kprobes.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 2d27ec4feee4..9b340af02c38 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -264,6 +264,9 @@ int kprobe_handler(struct pt_regs *regs)
 	if (user_mode(regs))
 		return 0;
 
+	if (!(regs->msr & MSR_IR) || !(regs->msr & MSR_DR))
+		return 0;
+
 	/*
 	 * We don't want to be preempted for the entire
 	 * duration of kprobe processing
-- 
2.25.0