[PATCH 06/39] arm64: entry: Ensure branch through syscall table is bounded under speculation
Alex Shi
alex.shi at linaro.org
Fri Mar 9 01:06:49 PST 2018
From: Will Deacon <will.deacon at arm.com>
commit 6314d90e6493 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 at arm.com>
Signed-off-by: Will Deacon <will.deacon at arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
Signed-off-by: Alex Shi <alex.shi at linaro.org>
---
arch/arm64/include/asm/assembler.h | 11 +++++++++++
arch/arm64/kernel/entry.S | 1 +
2 files changed, 12 insertions(+)
diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index 229b37ddf52c..81a5f416a27a 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -101,6 +101,17 @@
hint #20
.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
*/
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 274898465a3f..166cd6626ca7 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -694,6 +694,7 @@ 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
--
2.16.2.440.gc6284da
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