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Subject[PATCH 4.14 65/75] powerpc/jprobes: Disable preemption when triggered through ftrace
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>

commit 6baea433bc84cd148af1c524389a8d756f67412e upstream.

KPROBES_SANITY_TEST throws the below splat when CONFIG_PREEMPT is
enabled:

Kprobe smoke test: started
DEBUG_LOCKS_WARN_ON(val > preempt_count())
------------[ cut here ]------------
WARNING: CPU: 19 PID: 1 at kernel/sched/core.c:3094 preempt_count_sub+0xcc/0x140
Modules linked in:
CPU: 19 PID: 1 Comm: swapper/0 Not tainted 4.13.0-rc7-nnr+ #97
task: c0000000fea80000 task.stack: c0000000feb00000
NIP: c00000000011d3dc LR: c00000000011d3d8 CTR: c000000000a090d0
REGS: c0000000feb03400 TRAP: 0700 Not tainted (4.13.0-rc7-nnr+)
MSR: 8000000000021033 <SF,ME,IR,DR,RI,LE> CR: 28000282 XER: 00000000
CFAR: c00000000015aa18 SOFTE: 0
<snip>
NIP preempt_count_sub+0xcc/0x140
LR preempt_count_sub+0xc8/0x140
Call Trace:
preempt_count_sub+0xc8/0x140 (unreliable)
kprobe_handler+0x228/0x4b0
program_check_exception+0x58/0x3b0
program_check_common+0x16c/0x170
--- interrupt: 0 at kprobe_target+0x8/0x20
LR = init_test_probes+0x248/0x7d0
kp+0x0/0x80 (unreliable)
livepatch_handler+0x38/0x74
init_kprobes+0x1d8/0x208
do_one_initcall+0x68/0x1d0
kernel_init_freeable+0x298/0x374
kernel_init+0x24/0x160
ret_from_kernel_thread+0x5c/0x70
Instruction dump:
419effdc 3d22001b 39299240 81290000 2f890000 409effc8 3c82ffcb 3c62ffcb
3884bc68 3863bc18 4803d5fd 60000000 <0fe00000> 4bffffa8 60000000 60000000
---[ end trace 432dd46b4ce3d29f ]---
Kprobe smoke test: passed successfully

The issue is that we aren't disabling preemption in
kprobe_ftrace_handler(). Disable it.

Fixes: ead514d5fb30a0 ("powerpc/kprobes: Add support for KPROBES_ON_FTRACE")
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
[mpe: Trim oops a little for formatting]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/powerpc/kernel/kprobes-ftrace.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)

--- a/arch/powerpc/kernel/kprobes-ftrace.c
+++ b/arch/powerpc/kernel/kprobes-ftrace.c
@@ -65,6 +65,7 @@ void kprobe_ftrace_handler(unsigned long
/* Disable irq for emulating a breakpoint and avoiding preempt */
local_irq_save(flags);
hard_irq_disable();
+ preempt_disable();

p = get_kprobe((kprobe_opcode_t *)nip);
if (unlikely(!p) || kprobe_disabled(p))
@@ -86,12 +87,18 @@ void kprobe_ftrace_handler(unsigned long
kcb->kprobe_status = KPROBE_HIT_ACTIVE;
if (!p->pre_handler || !p->pre_handler(p, regs))
__skip_singlestep(p, regs, kcb, orig_nip);
- /*
- * If pre_handler returns !0, it sets regs->nip and
- * resets current kprobe.
- */
+ else {
+ /*
+ * If pre_handler returns !0, it sets regs->nip and
+ * resets current kprobe. In this case, we still need
+ * to restore irq, but not preemption.
+ */
+ local_irq_restore(flags);
+ return;
+ }
}
end:
+ preempt_enable_no_resched();
local_irq_restore(flags);
}
NOKPROBE_SYMBOL(kprobe_ftrace_handler);

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