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

From: Masami Hiramatsu <[email-masked]>
Date: Fri, 02 May 2014 10:13:43 +0900

(2014/05/01 14:26), Vineet Gupta wrote:
> 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]>

Acked-by: Masami Hiramatsu <[email-masked]>

Thanks!

> ---
>  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
> 

-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: [email-masked]