linux-kernel - Re: [PATCH v4] kprobes: arm: enable OPTPROBES for ARM 32

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 13 Aug 2014 00:12:55 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	"Jon Medhurst (Tixy)" <tixy@...aro.org>, ananth@...ibm.com,
	anil.s.keshavamurthy@...el.com, davem@...emloft.net,
	Will Deacon <will.deacon@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	peifeiyue@...wei.com, lizefan@...wei.com
Subject: Re: [PATCH v4] kprobes: arm: enable OPTPROBES for ARM 32

(2014/08/12 22:03), Wang Nan wrote:
> Hi Masami and everyone,
> 
> When checking my code I found a problem: if we replace a stack operatinon instruction,
> it is possible that the emulate execution of such instruction destroy the stack used
> by kprobeopt:
> 
>> +
>> +asm (
>> +			".global optprobe_template_entry\n"
>> +			"optprobe_template_entry:\n"
>> +			"	sub	sp, sp, #80\n"
>> +			"	stmia	sp, {r0 - r14} \n"
> 
> Here, trampoline code sub sp with 80 (0x50, I choose this number without much thinking), and then
> use stmia to push r0 - r14 (registers except pc) onto the stack. Assume the original sp is
> 0xd0000050, the stack becomes:
> 
> 0xd0000000: r0
> 0xd0000004: r1
> 0xd0000008: r2
> ...
> 0xd0000038: r14
> 0xd000003c: r15 (place holder)
> 0xd0000040: cpsr (place holder)
> 0xd0000044: ?
> 0xd0000048: ?
> 0xd000004c: ?
> 0xd0000050: original stack
> 
> If the replaced code operates stack, for example, push {r0 - r10}, it will overwrite our register.
> For that reason, sub sp, #80 is not enough, we need at least 64 bytes stack space, so the first instruction
> here should be sub sp, #128.
> 
> However, it increase stack requirement. Moreover, although rare, there may be sp relative addressing,
> such as: str r1, [sp, #-132].

Hmm, I see the increasing stack is clearly hard to emulate, but
why is it hard to emulate sp relative instruction? It should
access the memory under the stack pointer.

> To make every situations safe, do you think we need to alloc a pre-cpu optprobe private stack?

Of course, that is one possible idea, but the simplest way is just not
optimizing such instructions. Why not can_optimize() check that? ;)

Thank you,

-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/