[PATCH 4.16 106/279] arm64: fix possible spectre-v1 in ptrace_hbp_get_event()

[Greg Kroah-Hartman]

4.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mark Rutland <mark.rutland@xxxxxxx>

[ Upstream commit 19791a7ca674fb3009bb068260e852a2f05b605c ]

It's possible for userspace to control idx. Sanitize idx when using it
as an array index.

Found by smatch.

Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/arm64/kernel/ptrace.c |   14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -25,6 +25,7 @@
 #include <linux/sched/signal.h>
 #include <linux/sched/task_stack.h>
 #include <linux/mm.h>
+#include <linux/nospec.h>
 #include <linux/smp.h>
 #include <linux/ptrace.h>
 #include <linux/user.h>
@@ -249,15 +250,20 @@ static struct perf_event *ptrace_hbp_get
 
 	switch (note_type) {
 	case NT_ARM_HW_BREAK:
-		if (idx < ARM_MAX_BRP)
-			bp = tsk->thread.debug.hbp_break[idx];
+		if (idx >= ARM_MAX_BRP)
+			goto out;
+		idx = array_index_nospec(idx, ARM_MAX_BRP);
+		bp = tsk->thread.debug.hbp_break[idx];
 		break;
 	case NT_ARM_HW_WATCH:
-		if (idx < ARM_MAX_WRP)
-			bp = tsk->thread.debug.hbp_watch[idx];
+		if (idx >= ARM_MAX_WRP)
+			goto out;
+		idx = array_index_nospec(idx, ARM_MAX_WRP);
+		bp = tsk->thread.debug.hbp_watch[idx];
 		break;
 	}
 
+out:
 	return bp;
 }