linux-kernel - Re: [RFC] [PATCH] To vunmap correct address in text

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Date:	Wed, 25 Jul 2007 19:41:17 +0530
From:	"S. P. Prasanna" <prasanna@...ibm.com>
To:	Srinivasa Ds <srinivasa@...ibm.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>, ananth@...ibm.com,
	anil.s.keshavamurthy@...el.com, jkenisto@...ibm.com,
	systemtap@...rces.redhat.com, suzuki@...ibm.com
Subject: Re: [RFC] [PATCH] To vunmap correct address in text_poke()(kprobes)

On Wed, Jul 25, 2007 at 12:21:49PM +0530, Srinivasa Ds wrote:
> 
> When I was testing kprobes on x86_64 and I come across the below error message 
> on latest 2.6.23-rc1 kernel.
> ==========================================
> Trying to vfree() bad address (ffffc20002233199)
>  WARNING: at mm/vmalloc.c:330 __vunmap()
> 
>  Call Trace:
>  [<ffffffff8023d199>] sys_gettimeofday+0x0/0x62
>   [<ffffffff8047636c>] text_poke+0x119/0x124
>   [<ffffffff80476b42>] arch_arm_kprobe+0x1c/0x21
>   [<ffffffff80477cfd>] __register_kprobe+0x28a/0x2ed
>   [<ffffffff8815a039>] :gettimeofday:kprobe_init+0x39/0x65
>   [<ffffffff8025b5cf>] sys_init_module+0x1626/0x1788
>   [<ffffffff802aaf12>] dput+0x3f/0xfa
>   [<ffffffff8026bf91>] audit_syscall_entry+0x141/0x174
>   [<ffffffff8020bee5>] tracesys+0xdc/0xe1
> 
> ======================================================
> 
> This indicates that vunmap() is not receving the page-aligned address in 
> text_poke(). So the below attached patch will address this issue. Please let 
> me know your comments.
> 
> Signed-off-by: Srinivasa DS <srinivasa@...ibm.com>
> Signed-off-by: Suzuki K P   <suzuki@...ibm.com>
> 
> 
> Index: linux-2.6.23-rc1/arch/i386/kernel/alternative.c
> ===================================================================
> --- linux-2.6.23-rc1.orig/arch/i386/kernel/alternative.c	2007-07-23 
> 02:11:00.000000000 +0530
> +++ linux-2.6.23-rc1/arch/i386/kernel/alternative.c	2007-07-25 
> 11:45:53.000000000 +0530
> @@ -447,5 +447,5 @@ void __kprobes text_poke(void *oaddr, un
>  	if (cpu_has_clflush)
>  		asm("clflush (%0) " :: "r" (oaddr) : "memory");
>  	if (addr != oaddr)
> -		vunmap(addr);
> +		vunmap(addr-(((unsigned long)oaddr) % PAGE_SIZE));
		
It is appropriate to use PAGE_MASK rather than doing all this,
as shown below.

		vunmap((u8 *)((unsigned long)addr & PAGE_MASK));

Thanks
Prasanna

-- 
Prasanna S.P.
Linux Technology Center
India Software Labs, IBM Bangalore
Email: prasanna@...ibm.com
Ph: 91-80-41776329
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