linux-kernel - Re: [PATCH 1/2] x86: make profile_pc() use arch_stack

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Date:   Fri, 7 Apr 2023 21:56:19 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Qi Zheng <zhengqi.arch@...edance.com>
Cc:     peterz@...radead.org, keescook@...omium.org,
        dave.hansen@...ux.intel.com, bp@...en8.de, mingo@...hat.com,
        tglx@...utronix.de, rostedt@...dmis.org, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Chen Zhongjin <chenzhongjin@...wei.com>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 1/2] x86: make profile_pc() use arch_stack_walk()

On Thu, Mar 30, 2023 at 04:15:51PM +0800, Qi Zheng wrote:
> The profile_pc() try to get pc by doing a trick to read
> the contents of the stack. This may cause false positives
> for KASAN, like the following:
> 
>  BUG: KASAN: stack-out-of-bounds in profile_pc+0x5b/0x90
>  Read of size 8 at addr ffff8881062a7a00 by task id/130040

I don't think this was actually a false positive.  The !FRAME_POINTER
code in profile_pc() has been badly broken for many years.

BTW, there was a similar patch here:

  https://lore.kernel.org/lkml/20230224021858.120078-1-chenzhongjin@huawei.com/

I thought CONFIG_PROFILING was obsolete but Andi said previously he
wants to keep it for at least boot-time profiling.

Andi did suggest removing the lock profiling hacks, which means all the
profile_pc() implementations can just be removed in favor of the generic
instruction_pointer().

-- 
Josh