From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: Wed, 4 Sep 2019 10:27:18 +0000 (+0200)
Subject: x86/ptrace: fix up botched merge of spectrev1 fix
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=69f692bb7e684592aaba779299bc576626d414b4;p=GitHub%2FLineageOS%2FG12%2Fandroid_kernel_amlogic_linux-4.9.git

x86/ptrace: fix up botched merge of spectrev1 fix

I incorrectly merged commit 31a2fbb390fe ("x86/ptrace: Fix possible
spectre-v1 in ptrace_get_debugreg()") when backporting it, as was
graciously pointed out at
https://grsecurity.net/teardown_of_a_failed_linux_lts_spectre_fix.php

Resolve the upstream difference with the stable kernel merge to properly
protect things.

Reported-by: Brad Spengler <spender@grsecurity.net>
Cc: Dianzhang Chen <dianzhangchen0@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: <bp@alien8.de>
Cc: <hpa@zytor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 8d20fb09722c..7f377f8792aa 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -651,11 +651,10 @@ static unsigned long ptrace_get_debugreg(struct task_struct *tsk, int n)
 {
 	struct thread_struct *thread = &tsk->thread;
 	unsigned long val = 0;
-	int index = n;
 
 	if (n < HBP_NUM) {
+		int index = array_index_nospec(n, HBP_NUM);
 		struct perf_event *bp = thread->ptrace_bps[index];
-		index = array_index_nospec(index, HBP_NUM);
 
 		if (bp)
 			val = bp->hw.info.address;