From: Will Deacon <will.deacon@arm.com>
Date: Mon, 5 Feb 2018 15:34:20 +0000
Subject: arm64: entry: Ensure branch through syscall table is bounded under
 speculation
Git-commit: 6314d90e64936c584f300a52ef173603fb2461b5
Patch-mainline: v4.16-rc1
References: bsc#1068032

In a similar manner to array_index_mask_nospec, this patch introduces an
assembly macro (mask_nospec64) which can be used to bound a value under
speculation. This macro is then used to ensure that the indirect branch
through the syscall table is bounded under speculation, with out-of-range
addresses speculating as calls to sys_io_setup (0).

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
[mb: use scno and sc_nr instead of xscno and xsc_nr]
Signed-off-by: Matthias Brugger <mbrugger@suse.com>
---
 arch/arm64/include/asm/assembler.h |   11 +++++++++++
 arch/arm64/kernel/entry.S          |    1 +
 2 files changed, 12 insertions(+)

--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -115,6 +115,17 @@
 	.endm
 
 /*
+ * Sanitise a 64-bit bounded index wrt speculation, returning zero if out
+ * of bounds.
+ */
+	.macro	mask_nospec64, idx, limit, tmp
+	sub	\tmp, \idx, \limit
+	bic	\tmp, \tmp, \idx
+	and	\idx, \idx, \tmp, asr #63
+	csdb
+	.endm
+
+/*
  * NOP sequence
  */
 	.macro	nops, num
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -901,6 +901,7 @@ el0_svc_naked:					// compat entry point
 	b.ne	__sys_trace
 	cmp     scno, sc_nr                     // check upper syscall limit
 	b.hs	ni_sys
+	mask_nospec64 scno, sc_nr, x19	// enforce bounds for syscall number
 	ldr	x16, [stbl, scno, lsl #3]	// address in the syscall table
 	blr	x16				// call sys_* routine
 	b	ret_fast_syscall