[PATCH 4.14 056/173] arm64: fix possible spectre-v1 write in ptrace_hbp_set_event()

[Greg Kroah-Hartman]

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

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

From: Mark Rutland <mark.rutl...@arm.com>

[ Upstream commit 14d6e289a89780377f8bb09de8926d3c62d763cd ]

It's possible for userspace to control idx. Sanitize idx when using it
as an array index, to inhibit the potential spectre-v1 write gadget.

Found by smatch.

Signed-off-by: Mark Rutland <mark.rutl...@arm.com>
Cc: Catalin Marinas <catalin.mari...@arm.com>
Cc: Will Deacon <will.dea...@arm.com>
Signed-off-by: Will Deacon <will.dea...@arm.com>
Signed-off-by: Sasha Levin <alexander.le...@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 arch/arm64/kernel/ptrace.c |   19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -274,19 +274,22 @@ static int ptrace_hbp_set_event(unsigned
 
        switch (note_type) {
        case NT_ARM_HW_BREAK:
-               if (idx < ARM_MAX_BRP) {
-                       tsk->thread.debug.hbp_break[idx] = bp;
-                       err = 0;
-               }
+               if (idx >= ARM_MAX_BRP)
+                       goto out;
+               idx = array_index_nospec(idx, ARM_MAX_BRP);
+               tsk->thread.debug.hbp_break[idx] = bp;
+               err = 0;
                break;
        case NT_ARM_HW_WATCH:
-               if (idx < ARM_MAX_WRP) {
-                       tsk->thread.debug.hbp_watch[idx] = bp;
-                       err = 0;
-               }
+               if (idx >= ARM_MAX_WRP)
+                       goto out;
+               idx = array_index_nospec(idx, ARM_MAX_WRP);
+               tsk->thread.debug.hbp_watch[idx] = bp;
+               err = 0;
                break;
        }
 
+out:
        return err;
 }