linux-kernel - Re: [PATCH] riscv: kprobe: Fixup misaligned load text

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Message-ID: <87tu05pvur.fsf@all.your.base.are.belong.to.us>
Date:   Wed, 01 Feb 2023 10:40:12 +0100
From:   Björn Töpel <bjorn@...nel.org>
To:     guoren@...nel.org, guoren@...nel.org, palmer@...osinc.com,
        conor.dooley@...rochip.com, liaochang1@...wei.com
Cc:     linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org,
        Guo Ren <guoren@...ux.alibaba.com>,
        Bjorn Topel <bjorn.topel@...il.com>
Subject: Re: [PATCH] riscv: kprobe: Fixup misaligned load text

guoren@...nel.org writes:

> From: Guo Ren <guoren@...ux.alibaba.com>
>
> The current kprobe would cause a misaligned load for the probe point.
> This patch fixup it with two half-word loads instead.
>
> Fixes: c22b0bcb1dd0 ("riscv: Add kprobes supported")
> Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
> Signed-off-by: Guo Ren <guoren@...nel.org>
> Link: https://lore.kernel.org/linux-riscv/878rhig9zj.fsf@all.your.base.are.belong.to.us/
> Reported-by: Bjorn Topel <bjorn.topel@...il.com>
> ---
>  arch/riscv/kernel/probes/kprobes.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
> index 41c7481afde3..c1160629cef4 100644
> --- a/arch/riscv/kernel/probes/kprobes.c
> +++ b/arch/riscv/kernel/probes/kprobes.c
> @@ -74,7 +74,9 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
>  		return -EILSEQ;
>  
>  	/* copy instruction */
> -	p->opcode = *p->addr;
> +	p->opcode = (kprobe_opcode_t)(*(u16 *)probe_addr);
> +	if (GET_INSN_LENGTH(p->opcode) == 4)
> +		p->opcode |= (kprobe_opcode_t)(*(u16 *)(probe_addr + 2))
>  	<< 16;

Ugh, those casts. :-( What about the memcpy variant you had in the other
thread?