linux-kernel - Re: [PATCH V4 4/8] riscv: traps: Add noinstr to prevent instrumentation inserted

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Date:   Sun, 11 Sep 2022 17:09:25 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Guo Ren <guoren@...nel.org>
Cc:     arnd@...db.de, palmer@...osinc.com, tglx@...utronix.de,
        luto@...nel.org, conor.dooley@...rochip.com, heiko@...ech.de,
        jszhang@...nel.org, lazyparser@...il.com, falcon@...ylab.org,
        chenhuacai@...nel.org, apatel@...tanamicro.com,
        atishp@...shpatra.org, palmer@...belt.com,
        paul.walmsley@...ive.com, bigeasy@...utronix.de,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH V4 4/8] riscv: traps: Add noinstr to prevent
 instrumentation inserted

On Sat, Sep 10, 2022 at 05:17:44PM +0800, Guo Ren wrote:

> > > -asmlinkage __visible __trap_section void name(struct pt_regs *regs)  \
> > > +asmlinkage __visible __trap_section void noinstr name(struct pt_regs *regs)  \
> >
> > But now you have __trap_section and noinstr both adding a section
> > attribute.
> 
> Oops, thx for correcting. Here is my solution.
> 
> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> index 635e6ec26938..eba744caa711 100644
> --- a/arch/riscv/kernel/traps.c
> +++ b/arch/riscv/kernel/traps.c
> @@ -92,9 +92,11 @@ static void do_trap_error(struct pt_regs *regs, int
> signo, int code,
>  }
> 
>  #if defined(CONFIG_XIP_KERNEL) && defined(CONFIG_RISCV_ALTERNATIVE)
> -#define __trap_section         __section(".xip.traps")
> +#define __trap_section                                                 \
> +       noinline notrace __attribute((__section__(".xip.traps")))       \
> +       __no_kcsan __no_sanitize_address __no_profile __no_sanitize_coverage
>  #else
> -#define __trap_section
> +#define __trap_section noinstr
>  #endif

This is almost guaranteed to get out of sync when the compiler guys add
yet another sanitizier. Please consider picking up this patch:

  https://lore.kernel.org/all/20211110115736.3776-7-jiangshanlai@gmail.com/

and using __noinstr_section(".xip.traps")