linux-kernel - Re: radeon.ko/i586: BUG: kernel NULL pointer dereference, address:00000004

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Message-ID: <20230717113623.41878887@gandalf.local.home>
Date:   Mon, 17 Jul 2023 11:36:23 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     <kkabe@...a.pgw.jp>
Cc:     regressions@...ts.linux.dev, bagasdotme@...il.com,
        alexander.deucher@....com, christian.koenig@....com,
        Xinhui.Pan@....com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
        linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org
Subject: Re: radeon.ko/i586: BUG: kernel NULL pointer dereference,
 address:00000004

On Fri, 14 Jul 2023 14:34:04 +0900
<kkabe@...a.pgw.jp> wrote:

> Patch in
> https://bugzilla.kernel.org/show_bug.cgi?id=217669#c4
> fixed the problem in freedesktop.org kernel 5.18.0-rc2 .
> This may explain that in kernel.org tree, the said commit is in kernel-5.19.

You mean the patch that adds:

	#if defined(FTRACE_MCOUNT_MAX_OFFSET) && (FTRACE_MCOUNT_MAX_OFFSET)

?

Nothing should be setting FTRACE_MCOUNT_MAX_OFFSET to anything but non
zero. But doing a grep, I now see:

# define FTRACE_MCOUNT_MAX_OFFSET ENDBR_INSN_SIZE

Where it breaks that assumption if ENDBR_INSN_SIZE == 0 :-p
 (and that's my code!)

OK, does this fix it? (I haven't tested nor compiled this)

-- Steve

diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
index 897cf02c20b1..801f4414da3e 100644
--- a/arch/x86/include/asm/ftrace.h
+++ b/arch/x86/include/asm/ftrace.h
@@ -13,7 +13,7 @@
 #ifdef CONFIG_HAVE_FENTRY
 # include <asm/ibt.h>
 /* Add offset for endbr64 if IBT enabled */
-# define FTRACE_MCOUNT_MAX_OFFSET	ENDBR_INSN_SIZE
+# define FTRACE_MCOUNT_MAX_OFFSET	(ENDBR_INSN_SIZE + MCOUNT_INSN_SIZE)
 #endif
 
 #ifdef CONFIG_DYNAMIC_FTRACE