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

[Mark Rutland]

On Wed, Oct 10, 2018 at 06:45:17AM +0000, Chunhui Li (ææè) 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