linux-kernel - Re: [PATCH] x86: profiling: Using generic unwinding in profile

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Date:   Mon, 3 Apr 2023 09:24:19 +0800
From:   Chen Zhongjin <chenzhongjin@...wei.com>
To:     "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: Re: [PATCH] x86: profiling: Using generic unwinding in profile_pc

Just ping... Or has profile code already been obsoleted?

On 2023/2/24 10:18, chenzhongjin wrote:
> Syzbot has been reporting the problem of stack-out-of-bounds in
> profile_pc for a long time:
> https://syzkaller.appspot.com/bug?extid=84fe685c02cd112a2ac3
>
> profile_pc tries to get pc if current regs is inside lock function. For
> !CONFIG_FRAME_POINTER it used a hack way to get the pc from stack, which
> is not work with ORC. It makes profile_pc returns wrong result, and
> frequently triggers KASAN.
>
> This can be fixed by using the unwind_start, it will skip the first
> regs frame and get the caller of lock function directly, or 0 if
> unwind_get_return_address finds the unwinding failed. For all of FP, ORC
> and guess unwinders it works.
>
> Fixes: 0cb91a229364 ("[PATCH] i386: Account spinlocks to the caller during profiling for !FP kernels")
> Reported-by: syzbot+84fe685c02cd112a2ac3@...kaller.appspotmail.com
> Signed-off-by: Chen Zhongjin <chenzhongjin@...wei.com>
> ---
>   arch/x86/kernel/time.c | 20 ++++++--------------
>   1 file changed, 6 insertions(+), 14 deletions(-)
>
> diff --git a/arch/x86/kernel/time.c b/arch/x86/kernel/time.c
> index e42faa792c07..5e0446f49906 100644
> --- a/arch/x86/kernel/time.c
> +++ b/arch/x86/kernel/time.c
> @@ -24,26 +24,18 @@
>   #include <asm/timer.h>
>   #include <asm/hpet.h>
>   #include <asm/time.h>
> +#include <asm/unwind.h>
>   
>   unsigned long profile_pc(struct pt_regs *regs)
>   {
>   	unsigned long pc = instruction_pointer(regs);
>   
>   	if (!user_mode(regs) && in_lock_functions(pc)) {
> -#ifdef CONFIG_FRAME_POINTER
> -		return *(unsigned long *)(regs->bp + sizeof(long));
> -#else
> -		unsigned long *sp = (unsigned long *)regs->sp;
> -		/*
> -		 * Return address is either directly at stack pointer
> -		 * or above a saved flags. Eflags has bits 22-31 zero,
> -		 * kernel addresses don't.
> -		 */
> -		if (sp[0] >> 22)
> -			return sp[0];
> -		if (sp[1] >> 22)
> -			return sp[1];
> -#endif
> +		struct unwind_state state;
> +
> +		/* unwind_start will skip the first regs frame */
> +		unwind_start(&state, current, regs, NULL);
> +		pc = unwind_get_return_address(&state);
>   	}
>   	return pc;
>   }