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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     Mark Rutland <mark.rutland@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL 4.18 64/88] arm64: fix possible spectre-v1 write in
 ptrace_hbp_set_event()
Thread-Topic: [PATCH AUTOSEL 4.18 64/88] arm64: fix possible spectre-v1 write
 in ptrace_hbp_set_event()
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Date:   Fri, 7 Sep 2018 00:36:38 +0000
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From: Mark Rutland <mark.rutland@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.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 arch/arm64/kernel/ptrace.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 5c338ce5a7fa..db5440339ab3 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -277,19 +277,22 @@ static int ptrace_hbp_set_event(unsigned int note_typ=
e,
=20
 	switch (note_type) {
 	case NT_ARM_HW_BREAK:
-		if (idx < ARM_MAX_BRP) {
-			tsk->thread.debug.hbp_break[idx] =3D bp;
-			err =3D 0;
-		}
+		if (idx >=3D ARM_MAX_BRP)
+			goto out;
+		idx =3D array_index_nospec(idx, ARM_MAX_BRP);
+		tsk->thread.debug.hbp_break[idx] =3D bp;
+		err =3D 0;
 		break;
 	case NT_ARM_HW_WATCH:
-		if (idx < ARM_MAX_WRP) {
-			tsk->thread.debug.hbp_watch[idx] =3D bp;
-			err =3D 0;
-		}
+		if (idx >=3D ARM_MAX_WRP)
+			goto out;
+		idx =3D array_index_nospec(idx, ARM_MAX_WRP);
+		tsk->thread.debug.hbp_watch[idx] =3D bp;
+		err =3D 0;
 		break;
 	}
=20
+out:
 	return err;
 }
=20
--=20
2.17.1