Intial Thumb2 Sandbox (naclrev 6680)

src/trusted/validator_arm/testdata-thumb/test_external_jumps.S

+@ Copyright (c) 2011 The Native Client Authors.  All rights reserved.
+@ Use of this source code is governed by a BSD-style license that can be
+@ found in the LICENSE file.
+
+.code 16
+.syntax unified
+.globl _start
+.thumb_func
+_start:
+  @ Note: For some reason the start symbol does _NOT_ have the one bit set.
+  @ We test bundle-aligned and bundle-unaligned versions of jumps.
+
+  @ Jump backwards to addresses that wrap around and have the top bit set.
+  @ Such destinations are outside the sandbox's address space and so
+  @ could be dangerous, although it's unlikely that anything is mapped
+  @ here in the range that an ARM jump instruction could reach.
+  b _start - 0x20000   @ disallowed
+  b _start - 0x20004   @ disallowed
+
+  @ Jump backwards to the syscall trampoline page.
+  b _start - 0x8000      @ allowed
+  b _start - 0x73FC      @ disallowed
+  b _start - 0x7fef      @ allowed (16-aligned but not 32-aligned)
+  b _start - 0x7fdf      @ allowed (32-aligned)
+  b _start - 0x7020      @ allowed
+  b _start - 0x1003      @ disallowed
+
+  @ Jump forwards to addresses outside this chunk of code.
+  b _start + 0x1000      @ allowed
+  b _start + 0x1004      @ disallowed
+
+  @ Jump forwards further.
+  b _start + 0x100000   @ allowed
+  b _start + 0x100004   @ disallowed
+
+  @ Jump to zero page.
+  @ This is intended to be "b 0b111", but the assembler crashes if I write that.
+  @ Obviously this assumes that _start == 0x20000.
+  b _start - 0x10000     @ allowed (0b111)
+  b _start - 0x0fffc     @ disallowed
+
+  b end_of_code          @ allowed
+
+end_of_code:
+  mov r0, r0             @ Necessary for jumping here to be legal (otherwise cs stops short, and umapped regions are treated like trampolines.