linux-kernel - Re: [PATCH] riscv: kprobe: Fixup kernel panic when probing an illegal position

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Message-ID: <87357pravt.fsf@all.your.base.are.belong.to.us>
Date:   Wed, 01 Feb 2023 10:30:14 +0100
From:   Björn Töpel <bjorn@...nel.org>
To:     Guo Ren <guoren@...nel.org>
Cc:     palmer@...belt.com, paul.walmsley@...ive.com, mhiramat@...nel.org,
        conor.dooley@...rochip.com, penberg@...nel.org,
        mark.rutland@....com, liaochang <liaochang1@...wei.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH] riscv: kprobe: Fixup kernel panic when probing an
 illegal position

Guo Ren <guoren@...nel.org> writes:

>> > +     if (!arch_check_kprobe(p))
>> > +             return -EILSEQ;
>> > +
>> >       /* copy instruction */
>> >       p->opcode = *p->addr;
>>
>> Not related to your patch, but this can also trigger a misaligned load.
> After rereading the spec, misaligned load/store is not mandatory
> supported. (Although my machines and qemu are correct)

Yes. It would be great if it could be turned on by QEMU (you can with
Spike).

> So I need fixup:
>
> diff --git a/arch/riscv/kernel/probes/kprobes.c
> b/arch/riscv/kernel/probes/kprobes.c
> index 27f8960c321c..0c016d496746 100644
> --- a/arch/riscv/kernel/probes/kprobes.c
> +++ b/arch/riscv/kernel/probes/kprobes.c
> @@ -58,12 +58,14 @@ static bool __kprobes arch_check_kprobe(struct kprobe *p)
>  {
>         unsigned long tmp  = (unsigned long)p->addr - p->offset;
>         unsigned long addr = (unsigned long)p->addr;
> +       kprobe_opcode_t opcode;
>
>         while (tmp <= addr) {
>                 if (tmp == addr)
>                         return true;
>
> -               tmp += GET_INSN_LENGTH(*(kprobe_opcode_t *)tmp);
> +               memcpy(&opcode, (void *)tmp, sizeof(kprobe_opcode_t));
> +               tmp += GET_INSN_LENGTH(opcode);

I'd prefer sizeof(opcode).

>         }
>
>         return false;
> @@ -80,7 +82,7 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
>                 return -EILSEQ;
>
>         /* copy instruction */
> -       p->opcode = *p->addr;
> +       memcpy(&p->opcode, p->addr, sizeof(kprobe_opcode_t));

Same comment as above, and this would ideally be a separate patch.


Björn