Commit f3ed64a6 authored Apr 12, 2018 by Mark Rutland Committed by Greg Kroah-Hartman Apr 20, 2018

arm64: entry: Ensure branch through syscall table is bounded under speculation




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]
Tested-by: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 891bea95

arch/arm64/include/asm/assembler.h

+11 −0

Original line number	Diff line number	Diff line
		@@ -93,6 +93,17 @@
		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
		*/

arch/arm64/kernel/entry.S

+1 −0

Original line number	Diff line number	Diff line
		@@ -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