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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Brad Spengler <spender@grsecurity.net>,
        Dianzhang Chen <dianzhangchen0@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>, bp@alien8.de,
        hpa@zytor.com
Subject: [PATCH 5.2 141/143] x86/ptrace: fix up botched merge of spectrev1 fix
Date:   Wed,  4 Sep 2019 19:54:44 +0200
Message-Id: <20190904175319.981793215@linuxfoundation.org>
In-Reply-To: <20190904175314.206239922@linuxfoundation.org>
References: <20190904175314.206239922@linuxfoundation.org>
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From: Greg Kroah-Hartman <gregkh@linuxfoundation.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@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>
---
 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
@@ -644,11 +644,10 @@ 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;