linux-kernel - Re: [PATCH] arm64: kprobe: fix an error in single stepping support

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Message-ID: <Z4N9y8XpblDoI5Jp@e129823.arm.com>
Date: Sun, 12 Jan 2025 08:31:07 +0000
From: Yeoreum Yun <yeoreum.yun@....com>
To: 1534428646@...com
Cc: catalin.marinas@....com, will@...nel.org, mark.rutland@....com,
	kristina.martsenko@....com, liaochang1@...wei.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] arm64: kprobe: fix an error in single stepping support

Hi Yiren,

> From: "Yiren.Xie" <1534428646@...com>
>
> It is obvious a conflict between the code and the comment.
> And verified that with this modification it can read the DAIF status.
>
> Signed-off-by: Yiren.Xie <1534428646@...com>
> ---
>  arch/arm64/kernel/probes/decode-insn.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/probes/decode-insn.c b/arch/arm64/kernel/probes/decode-insn.c
> index 6438bf62e753..22383eb1c22c 100644
> --- a/arch/arm64/kernel/probes/decode-insn.c
> +++ b/arch/arm64/kernel/probes/decode-insn.c
> @@ -40,7 +40,7 @@ static bool __kprobes aarch64_insn_is_steppable(u32 insn)
>  		 */
>  		if (aarch64_insn_is_mrs(insn))
>  			return aarch64_insn_extract_system_reg(insn)
> -			     != AARCH64_INSN_SPCLREG_DAIF;
> +			     == AARCH64_INSN_SPCLREG_DAIF;
>
>  		/*
>  		 * The HINT instruction is steppable only if it is in whitelist

Nit:
When single-stepped, the DAIF bits are set, in setup_singlesteup(),
Reading a DAIF via mrs instruction isn't correct value as comments
describe.

What is conflict?

Thanks.