kprobes broken in linux-next (was Re: [tip:perf/kprobes] kprobes: Introduce NOKPROBE_SYMBOL() macro to maintain kprobes blacklist)

Vineet Gupta
2014-05-01T05:29:04Z

On Thursday 24 April 2014 04:28 PM, tip-bot for Masami Hiramatsu wrote:
> Commit-ID: 376e242429bf8539ef39a080ac113c8799840b13
> Gitweb: http://git.kernel.org/tip/376e242429bf8539ef39a080ac113c8799840b13
> Author: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> AuthorDate: Thu, 17 Apr 2014 17:17:05 +0900
> Committer: Ingo Molnar <mingo@kernel.org>
> CommitDate: Thu, 24 Apr 2014 10:02:56 +0200
>
> kprobes: Introduce NOKPROBE_SYMBOL() macro to maintain kprobes blacklist
>
> Introduce NOKPROBE_SYMBOL() macro which builds a kprobes
> blacklist at kernel build time.
>
....

> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 146e4ff..40ceb3c 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -109,6 +109,14 @@
> #define BRANCH_PROFILE()
> #endif
>
> +#ifdef CONFIG_KPROBES
> +#define KPROBE_BLACKLIST() VMLINUX_SYMBOL(__start_kprobe_blacklist) = .; \
> + *(_kprobe_blacklist) \
> + VMLINUX_SYMBOL(__stop_kprobe_blacklist) = .;
> +#else
> +#define KPROBE_BLACKLIST()
> +#endif
> +
> #ifdef CONFIG_EVENT_TRACING
> #define FTRACE_EVENTS() . = ALIGN(8); \
> VMLINUX_SYMBOL(__start_ftrace_events) = .; \
> @@ -507,6 +515,7 @@
> *(.init.rodata) \
> FTRACE_EVENTS() \
> TRACE_SYSCALLS() \
> + KPROBE_BLACKLIST() \
> MEM_DISCARD(init.rodata) \
> CLK_OF_TABLES() \
> RESERVEDMEM_OF_TABLES() \

Linux-next fails to boot on ARC due to misaligned __start_kprobe_blacklist. Patch
below fixes it.

------------------------>
>From c5afc4ebf9c1c094a260e2aaff6c5b3106063039 Mon Sep 17 00:00:00 2001
From: Vineet Gupta <vgupta@synopsys.com>
Date: Thu, 1 May 2014 10:47:29 +0530
Subject: [PATCH] kprobes: Ensure blacklist data is aligned

ARC Linux (not supporting native unaligned access) was failing to boot
because __start_kprobe_blacklist was not aligned.

This was because per generated vmlinux.lds it was emitted right next
to .rodata with strings etc hence could be randomly unaligned.

Fix that by ensuring a word alignment. While 4 would suffice for 32bit
arches and problem at hand, it is probably better to put 8.

| Path: (null) CPU: 0 PID: 1 Comm: swapper Not tainted
| 3.15.0-rc3-next-20140430 #2
| task: 8f044000 ti: 8f01e000 task.ti: 8f01e000
|
| [ECR ]: 0x00230400 => Misaligned r/w from 0x800fb0d3
| [EFA ]: 0x800fb0d3
| [BLINK ]: do_one_initcall+0x86/0x1bc
| [ERET ]: init_kprobes+0x52/0x120

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
---
include/asm-generic/vmlinux.lds.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 40ceb3ceba79..8e0204a68c74 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -110,7 +110,8 @@
#endif

#ifdef CONFIG_KPROBES
-#define KPROBE_BLACKLIST() VMLINUX_SYMBOL(__start_kprobe_blacklist) = .; \
+#define KPROBE_BLACKLIST() . = ALIGN(8); \
+ VMLINUX_SYMBOL(__start_kprobe_blacklist) = .; \
*(_kprobe_blacklist) \
VMLINUX_SYMBOL(__stop_kprobe_blacklist) = .;
#else
--
1.8.3.2