From: Peter Zijlstra <peterz@infradead.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>,
Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCH v2] x86/kprobes: Fix 1 byte conditional jump target
Date: Wed, 8 Feb 2023 21:01:19 +0100 [thread overview]
Message-ID: <Y+P/j0FiocmavHTL@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20230208071708.4048-1-namit@vmware.com>
On Wed, Feb 08, 2023 at 07:17:08AM +0000, Nadav Amit 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 and instead
> zero-extended.
>
> In fact, there is no need for any casting of immediate.value since sign
> extension is already done during its decoding in insn_get_immediate().
>
> Fix by removing the casting of the 1 byte conditional jump target.
> Future patches can also remove the casting (and sign extension) in other
> cases in which immediate.value is being used.
>
> Fixes: 3bc753c06dd0 ("kbuild: treat char as always unsigned")
> Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> Suggested-by: Dave Hansen <dave.hansen@intel.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Nadav Amit <namit@vmware.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
next prev parent reply other threads:[~2023-02-08 20:01 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-08 7:17 [PATCH v2] x86/kprobes: Fix 1 byte conditional jump target Nadav Amit
2023-02-08 20:01 ` Peter Zijlstra [this message]
2023-02-09 14:24 ` Masami Hiramatsu
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