Re: [PATCH] arm64: ftrace: don't dereference a probably invalid address

From: Steven Rostedt <rostedt@goodmis.org>
To: Mark-PK Tsai <mark-pk.tsai@mediatek.com>
Cc: <catalin.marinas@arm.com>, <linux-arm-kernel@lists.infradead.org>,
	<linux-kernel@vger.kernel.org>,
	<linux-mediatek@lists.infradead.org>, <matthias.bgg@gmail.com>,
	<mingo@redhat.com>, <will@kernel.org>, <yj.chiang@mediatek.com>
Subject: Re: [PATCH] arm64: ftrace: don't dereference a probably invalid address
Date: Mon, 7 Jun 2021 10:52:17 -0400	[thread overview]
Message-ID: <20210607105217.772214e5@oasis.local.home> (raw)
In-Reply-To: <20210607141522.3281-1-mark-pk.tsai@mediatek.com>

On Mon, 7 Jun 2021 22:15:22 +0800
Mark-PK Tsai <mark-pk.tsai@mediatek.com> wrote:

> And the crash is becuase kernel trying to read *rec->ip in print_ip_ins() if
> ftrace_bug() get error code -EINVAL.

Right, so the actual fix should be something like this:

[ not tested, nor even compiled ]

-- Steve

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 2e8a3fde7104..72ef4dccbcc4 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1967,12 +1967,18 @@ static int ftrace_hash_ipmodify_update(struct ftrace_ops *ops,
 
 static void print_ip_ins(const char *fmt, const unsigned char *p)
 {
+	char ins[MCOUNT_INSN_SIZE];
 	int i;
 
+	if (copy_from_kernel_nofault(ins, p, MCOUNT_INSN_SIZE)) {
+		printk(KERN_CONT "%s[FAULT](%px)", fmt, p);
+		return;
+	}
+
 	printk(KERN_CONT "%s", fmt);
 
 	for (i = 0; i < MCOUNT_INSN_SIZE; i++)
-		printk(KERN_CONT "%s%02x", i ? ":" : "", p[i]);
+		printk(KERN_CONT "%s%02x", i ? ":" : "", ins[i]);
 }
 
 enum ftrace_bug_type ftrace_bug_type;
