linux-kernel - [PATCH] [BUGFIX] arm: kprobes: Fix to use get_kprobe

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Message-Id: <151937788067.22527.14819753928851623471.stgit@devbox>
Date:   Fri, 23 Feb 2018 18:24:40 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Russell King <linux@...linux.org.uk>
Cc:     Wang Nan <wangnan0@...wei.com>, Will Deacon <will.deacon@....com>,
        Jon Medhurst <tixy@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        mhiramat@...nel.org
Subject: [PATCH] [BUGFIX] arm: kprobes: Fix to use get_kprobe_ctlblk after irq-disabed

Since get_kprobe_ctlblk() uses smp_processor_id() to access
per-cpu variable, it hits smp_processor_id sanity check as below.

[    7.006928] BUG: using smp_processor_id() in preemptible [00000000] code: swapper/0/1
[    7.007859] caller is debug_smp_processor_id+0x20/0x24
[    7.008438] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.16.0-rc1-00192-g4eb17253e4b5 #1
[    7.008890] Hardware name: Generic DT based system
[    7.009917] [<c0313f0c>] (unwind_backtrace) from [<c030e6d8>] (show_stack+0x20/0x24)
[    7.010473] [<c030e6d8>] (show_stack) from [<c0c64694>] (dump_stack+0x84/0x98)
[    7.010990] [<c0c64694>] (dump_stack) from [<c071ca5c>] (check_preemption_disabled+0x138/0x13c)
[    7.011592] [<c071ca5c>] (check_preemption_disabled) from [<c071ca80>] (debug_smp_processor_id+0x20/0x24)
[    7.012214] [<c071ca80>] (debug_smp_processor_id) from [<c03335e0>] (optimized_callback+0x2c/0xe4)
[    7.013077] [<c03335e0>] (optimized_callback) from [<bf0021b0>] (0xbf0021b0)

To fix this issue, call get_kprobe_ctlblk() right after
irq-disabled since that disables preemption.

Fixes: 0dc016dbd820 ("ARM: kprobes: enable OPTPROBES for ARM 32")
Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 arch/arm/probes/kprobes/opt-arm.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm/probes/kprobes/opt-arm.c b/arch/arm/probes/kprobes/opt-arm.c
index bcdecc25461b..ddc5a82eb10d 100644
--- a/arch/arm/probes/kprobes/opt-arm.c
+++ b/arch/arm/probes/kprobes/opt-arm.c
@@ -165,13 +165,14 @@ optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
 {
 	unsigned long flags;
 	struct kprobe *p = &op->kp;
-	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+	struct kprobe_ctlblk *kcb;
 
 	/* Save skipped registers */
 	regs->ARM_pc = (unsigned long)op->kp.addr;
 	regs->ARM_ORIG_r0 = ~0UL;
 
 	local_irq_save(flags);
+	kcb = get_kprobe_ctlblk();
 
 	if (kprobe_running()) {
 		kprobes_inc_nmissed_count(&op->kp);