答复: 答复: [PATCH] kasan: avoid out-of-bounds in unwind_frame

From: "Chunhui Li (李春辉)" <chunhui.li@mediatek.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: "Catalin Marinas" <catalin.marinas@arm.com>,
	"Will Deacon" <will.deacon@arm.com>,
	"Matthias Brugger" <matthias.bgg@gmail.com>,
	"Marc Zyngier" <marc.zyngier@arm.com>,
	"Ard Biesheuvel" <ard.biesheuvel@linaro.org>,
	"James Morse" <james.morse@arm.com>,
	"Masahiro Yamada" <yamada.masahiro@socionext.com>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-mediatek@lists.infradead.org"
	<linux-mediatek@lists.infradead.org>,
	wsd_upstream <wsd_upstream@mediatek.com>,
	"Miles Chen (陳民樺)" <Miles.Chen@mediatek.com>,
	"Walter-ZH Wu (吳祖寰)" <Walter-ZH.Wu@mediatek.com>,
	"Yu Liang (梁宇)" <Yu.Liang@mediatek.com>,
	"Nicholas Tang (鄭秦輝)" <nicholas.tang@mediatek.com>
Subject: 答复: 答复: [PATCH] kasan: avoid out-of-bounds in unwind_frame
Date: Wed, 10 Oct 2018 11:20:16 +0000	[thread overview]
Message-ID: <a96f9343ed35422498432cc24405f39b@MTKMBS32N1.mediatek.inc> (raw)
In-Reply-To: <20181010092618.pwkrqqw7br7762rs@lakrids.cambridge.arm.com>

Hi Mark,

Ok, thanks for your help

Best regards,
Chunhui Li

-----邮件原件-----
发件人: Mark Rutland [mailto:mark.rutland@arm.com] 
发送时间: 2018年10月10日 17:26
收件人: Chunhui Li (李春辉)
抄送: Catalin Marinas; Will Deacon; Matthias Brugger; Marc Zyngier; Ard Biesheuvel; James Morse; Masahiro Yamada; linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org; linux-mediatek@lists.infradead.org; wsd_upstream; Miles Chen (陳民樺); Walter-ZH Wu (吳祖寰); Yu Liang (梁宇); Nicholas Tang (鄭秦輝)
主题: Re: 答复: [PATCH] kasan: avoid out-of-bounds in unwind_frame

On Wed, Oct 10, 2018 at 06:45:17AM +0000, Chunhui Li (李春辉) wrote:
> Hi Mark,
> 
> kasan detect out-of-bounds in stacktrace.c line 70, it's already over 
> READ_ONCE_NOCHECK, but still crash 
> kernel-4.9/arch/arm64/kernel/stacktrace.c
> 69frame->sp = fp + 0x10;
> 70frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
> 
> we test on Android platform, kernel-4.9 build with clang 6.0.2, we will do experiment to clarify whether compiler related issue.
> 
> READ_ONCE_NOCHECK->__read_once_size_nocheck with __no_sanitize_address 
> if enable CONFIG_KASAN
> 
> kernel-4.9/include/linux/compiler-gcc.h
> #define __no_sanitize_address __attribute__((no_sanitize_address))
> 
> kernel-4.9/include/linux/compiler-clang.h
> #define __no_sanitize_address __attribute__((no_sanitize("address")))

If READ_ONCE_NOCHECK() isn't working as intended, then this is a compiler issue, and there are bigger problems regardless.

If we need to workaround some compiler issue, that should be done in the implementation of READ_ONCE_NOCHECK().

Please note that there are other issues with using clang to compile the kernel; at minimum 7.0.0 is required to build a mainline kernel (and even then, the LSE atomics have to be explicitly disabled), so if this only affects 6.0.x, I don't think we need to carry any workaround upstream.

> there is patch from internet, avoid kasan by wrapping with kasan_disable_current, it seems better.
> https://lore.kernel.org/patchwork/patch/644463
> such as:
> +kasan_disable_current();
>   // access fp
> +kasan_enable_current();

Please note that the solution later in the thread [1] was to use READ_ONCE_NOCHECK().

Thanks,
Mark.

[1] https://lore.kernel.org/patchwork/patch/644463/#829858