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

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

[Mark Rutland]

On Tue, Oct 09, 2018 at 06:11:03PM +0800, Chunhui Li wrote:
> From: "chunhui.li" <chunhui.li@mediatek.com>
> 
>    kasan detect unwind_frame out-of-bounds error when one task
> dump another, log as below
> BUG: KASAN: out-of-bounds in unwind_frame+0x140/0x20c Read of
> size 8 at addr ffffffea1e2378e0 by task AnrMonitorThrea/1111
> avoid kasan out-of-bounds error by disable kasan for stacktrace.c

This doesn't look right. Since unwind_frame uses READ_ONCE_NOCHECK(),
we should never perform an access that KASAN complains about.

I don't think that we should completely disable instrumentation of
stacktrace.c.

Can you please figure out precisely which line KASAN is complaining
about? i.e. use scripts/faddr2line.

Thanks,
Mark.

> 
> Signed-off-by: chunhui.li <chunhui.li@mediatek.com>
> ---
>  arch/arm64/kernel/Makefile | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> index 95ac737..606d0e2 100644
> --- a/arch/arm64/kernel/Makefile
> +++ b/arch/arm64/kernel/Makefile
> @@ -57,6 +57,8 @@ arm64-obj-$(CONFIG_CRASH_DUMP)		+= crash_dump.o
>  arm64-obj-$(CONFIG_ARM_SDE_INTERFACE)	+= sdei.o
>  arm64-obj-$(CONFIG_ARM64_SSBD)		+= ssbd.o
>  
> +KASAN_SANITIZE_stacktrace.o := n
> +
>  obj-y					+= $(arm64-obj-y) vdso/ probes/
>  obj-m					+= $(arm64-obj-m)
>  head-y					:= head.o
> -- 
> 1.9.1
> 

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

[Chunhui Li (李春辉)]

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
69	frame->sp = fp + 0x10;
70	frame->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")))

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();

Thanks
Chunhui Li

-----邮件原件-----
发件人: Mark Rutland [mailto:mark.rutland@arm.com] 
发送时间: 2018年10月9日 18:39
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
主题: Re: [PATCH] kasan: avoid out-of-bounds in unwind_frame

On Tue, Oct 09, 2018 at 06:11:03PM +0800, Chunhui Li wrote:
> From: "chunhui.li" <chunhui.li@mediatek.com>
> 
>    kasan detect unwind_frame out-of-bounds error when one task dump 
> another, log as below
> BUG: KASAN: out-of-bounds in unwind_frame+0x140/0x20c Read of size 8 
> at addr ffffffea1e2378e0 by task AnrMonitorThrea/1111 avoid kasan 
> out-of-bounds error by disable kasan for stacktrace.c

This doesn't look right. Since unwind_frame uses READ_ONCE_NOCHECK(), we should never perform an access that KASAN complains about.

I don't think that we should completely disable instrumentation of stacktrace.c.

Can you please figure out precisely which line KASAN is complaining about? i.e. use scripts/faddr2line.

Thanks,
Mark.

> 
> Signed-off-by: chunhui.li <chunhui.li@mediatek.com>
> ---
>  arch/arm64/kernel/Makefile | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile 
> index 95ac737..606d0e2 100644
> --- a/arch/arm64/kernel/Makefile
> +++ b/arch/arm64/kernel/Makefile
> @@ -57,6 +57,8 @@ arm64-obj-$(CONFIG_CRASH_DUMP)		+= crash_dump.o
>  arm64-obj-$(CONFIG_ARM_SDE_INTERFACE)	+= sdei.o
>  arm64-obj-$(CONFIG_ARM64_SSBD)		+= ssbd.o
>  
> +KASAN_SANITIZE_stacktrace.o := n
> +
>  obj-y					+= $(arm64-obj-y) vdso/ probes/
>  obj-m					+= $(arm64-obj-m)
>  head-y					:= head.o
> --
> 1.9.1
> 

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

[Mark Rutland]

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

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

[Chunhui Li (李春辉)]

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