linux-kernel - [PATCH 4.4 77/77] x86/ptrace: fix up botched merge of spectrev1 fix

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Message-Id: <20190904175310.513008739@linuxfoundation.org>
Date:   Wed,  4 Sep 2019 19:54:04 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Brad Spengler <spender@...ecurity.net>,
        Dianzhang Chen <dianzhangchen0@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>, bp@...en8.de,
        hpa@...or.com
Subject: [PATCH 4.4 77/77] x86/ptrace: fix up botched merge of spectrev1 fix

From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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@...ecurity.net>
Cc: Dianzhang Chen <dianzhangchen0@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: <bp@...en8.de>
Cc: <hpa@...or.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kernel/ptrace.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -698,11 +698,10 @@ static unsigned long ptrace_get_debugreg
 {
 	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;