From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
To: Nadav Amit <nadav.amit@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, linux-kernel@vger.kernel.org,
Nadav Amit <namit@vmware.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH] x86/kprobes: Fix 1 byte conditional jump target
Date: Mon, 6 Feb 2023 23:18:25 +0900 [thread overview]
Message-ID: <20230206231825.9997d73ded8497df9006585d@kernel.org> (raw)
In-Reply-To: <20230204210807.3930-1-namit@vmware.com>
On Sat, 4 Feb 2023 21:08:07 +0000
Nadav Amit <nadav.amit@gmail.com> wrote:
> From: Nadav Amit <namit@vmware.com>
>
> Commit 3bc753c06dd0 ("kbuild: treat char as always unsigned") broke
> kprobes. Setting a probe-point on 1 byte conditional jump can cause the
> kernel to crash, as the branch target is not sign extended.
Oops, indeed!
>
> Fix by using s8 instead of char and use immediate.value instead of
> immediate.bytes for consistency.
Looks good to me. Thanks for finding this bug!
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Fixes: 3bc753c06dd0 ("kbuild: treat char as always unsigned")
Thank you!
>
> Cc: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Nadav Amit <namit@vmware.com>
> ---
> arch/x86/kernel/kprobes/core.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index b36f3c367cb2..6a56d56b3817 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -625,7 +625,7 @@ static int prepare_emulation(struct kprobe *p, struct insn *insn)
> /* 1 byte conditional jump */
> p->ainsn.emulate_op = kprobe_emulate_jcc;
> p->ainsn.jcc.type = opcode & 0xf;
> - p->ainsn.rel32 = *(char *)insn->immediate.bytes;
> + p->ainsn.rel32 = *(s8 *)&insn->immediate.value;
> break;
> case 0x0f:
> opcode = insn->opcode.bytes[1];
> --
> 2.34.1
>
--
Masami Hiramatsu (Google) <mhiramat@kernel.org>
next prev parent reply other threads:[~2023-02-06 14:18 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-04 21:08 [PATCH] x86/kprobes: Fix 1 byte conditional jump target Nadav Amit
2023-02-05 7:49 ` Nadav Amit
2023-02-06 14:19 ` Masami Hiramatsu
2023-02-06 14:18 ` Masami Hiramatsu [this message]
2023-02-06 18:42 ` Dave Hansen
2023-02-06 19:05 ` Nadav Amit
2023-02-06 22:38 ` Dave Hansen
2023-02-07 0:54 ` Masami Hiramatsu
2023-02-07 15:21 ` Masami Hiramatsu
2023-02-07 15:33 ` Dave Hansen
2023-02-08 6:34 ` Nadav Amit
2023-02-08 6:56 ` Dave Hansen
2023-02-08 6:58 ` Nadav Amit
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