From 31a2fbb390fee4231281b939e1979e810f945415 Mon Sep 17 00:00:00 2001
From: Dianzhang Chen <dianzhangchen0@gmail.com>
Date: Tue, 25 Jun 2019 23:30:17 +0800
Subject: [PATCH] x86/ptrace: Fix possible spectre-v1 in ptrace_get_debugreg()
Git-commit: 31a2fbb390fee4231281b939e1979e810f945415
Patch-mainline: v5.3-rc1
References: bnc#1149376, CVE-2019-15902

The index to access the threads ptrace_bps is controlled by userspace via
Syscall: sys_ptrace(), hence leading to a potential exploitation of the
Spectre variant 1 vulnerability.

The index can be controlled from:
    ptrace -> arch_ptrace -> ptrace_get_debugreg.

Fix this by sanitizing the user supplied index before using it access
thread->ptrace_bps.

Signed-off-by: Dianzhang Chen <dianzhangchen0@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: bp@alien8.de
Cc: hpa@zytor.com
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/1561476617-3759-1-git-send-email-dianzhangchen0@gmail.com
Signed-off-by: Michal Hocko <mhocko@suse.com>

---
 arch/x86/kernel/ptrace.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -24,6 +24,7 @@
 #include <linux/rcupdate.h>
 #include <linux/export.h>
 #include <linux/context_tracking.h>
+#include <linux/nospec.h>
 
 #include <linux/uaccess.h>
 #include <asm/pgtable.h>
@@ -653,7 +654,8 @@ static unsigned long ptrace_get_debugreg
 	unsigned long val = 0;
 
 	if (n < HBP_NUM) {
-		struct perf_event *bp = thread->ptrace_bps[n];
+		int index = array_index_nospec(n, HBP_NUM);
+		struct perf_event *bp = thread->ptrace_bps[index];
 
 		if (bp)
 			val = bp->hw.info.address;