From f3ed64a6273ebdc1ddf22262c4e5f724688b7393 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Thu, 12 Apr 2018 12:11:02 +0100 Subject: [PATCH] arm64: entry: Ensure branch through syscall table is bounded under speculation From: Will Deacon 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 Signed-off-by: Will Deacon Signed-off-by: Catalin Marinas [v4.9: use existing scno & sc_nr definitions] Signed-off-by: Mark Rutland [v4.9 backport] Tested-by: Greg Hackmann Signed-off-by: Greg Kroah-Hartman --- 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 b223b1b4d5cd..540c24f74837 100644 --- a/arch/arm64/include/asm/assembler.h +++ b/arch/arm64/include/asm/assembler.h @@ -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 */ 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