[v4.9.y,06/42] arm64: entry: Ensure branch through syscall table is bounded under speculation

Message ID 20180412111138.40990-7-mark.rutland@arm.com
State New
Headers show
Series
  • arm64 spectre patches
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Commit Message

Mark Rutland April 12, 2018, 11:11 a.m.
From: Will Deacon <will.deacon@arm.com>


commit 6314d90e64936c584f300a52ef173603fb2461b5 upstream.

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>

[v4.9: use existing scno & sc_nr definitions]
Signed-off-by: Mark Rutland <mark.rutland@arm.com> [v4.9 backport]

---
 arch/arm64/include/asm/assembler.h | 11 +++++++++++
 arch/arm64/kernel/entry.S          |  1 +
 2 files changed, 12 insertions(+)

-- 
2.11.0

Patch

diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index b223b1b4d5cd..540c24f74837 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -94,6 +94,17 @@ 
 	.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
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 3f1cd7a795bb..c154b1608405 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -795,6 +795,7 @@  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