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

From: Vineet Gupta <[email-masked]>
Date: Thu, 1 May 2014 10:56:44 +0530

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 <[email-masked]>
> AuthorDate: Thu, 17 Apr 2014 17:17:05 +0900
> Committer:  Ingo Molnar <[email-masked]>
> 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 <[email-masked]>
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 <[email-masked]>
---
 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