• Douglas Raillard's avatar
    Add support for GCC stack protection · 51faada7
    Douglas Raillard authored
    
    Introduce new build option ENABLE_STACK_PROTECTOR. It enables
    compilation of all BL images with one of the GCC -fstack-protector-*
    options.
    
    A new platform function plat_get_stack_protector_canary() is introduced.
    It returns a value that is used to initialize the canary for stack
    corruption detection. Returning a random value will prevent an attacker
    from predicting the value and greatly increase the effectiveness of the
    protection.
    
    A message is printed at the ERROR level when a stack corruption is
    detected.
    
    To be effective, the global data must be stored at an address
    lower than the base of the stacks. Failure to do so would allow an
    attacker to overwrite the canary as part of an attack which would void
    the protection.
    
    FVP implementation of plat_get_stack_protector_canary is weak as
    there is no real source of entropy on the FVP. It therefore relies on a
    timer's value, which could be predictable.
    
    Change-Id: Icaaee96392733b721fa7c86a81d03660d3c1bc06
    Signed-off-by: default avatarDouglas Raillard <douglas.raillard@arm.com>
    51faada7
bl2_entrypoint.S 4.83 KB
/*
 * Copyright (c) 2016-2017, ARM Limited and Contributors. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * Redistributions of source code must retain the above copyright notice, this
 * list of conditions and the following disclaimer.
 *
 * Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 *
 * Neither the name of ARM nor the names of its contributors may be used
 * to endorse or promote products derived from this software without specific
 * prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include <arch.h>
#include <asm_macros.S>
#include <bl_common.h>


	.globl	bl2_vector_table
	.globl	bl2_entrypoint


vector_base bl2_vector_table
	b	bl2_entrypoint
	b	report_exception	/* Undef */
	b	report_exception	/* SVC call */
	b	report_exception	/* Prefetch abort */
	b	report_exception	/* Data abort */
	b	report_exception	/* Reserved */
	b	report_exception	/* IRQ */
	b	report_exception	/* FIQ */


func bl2_entrypoint
	/*---------------------------------------------
	 * Save from r1 the extents of the trusted ram
	 * available to BL2 for future use.
	 * r0 is not currently used.
	 * ---------------------------------------------
	 */
 	mov	r11, r1

	/* ---------------------------------------------
	 * Set the exception vector to something sane.
	 * ---------------------------------------------
	 */
	ldr	r0, =bl2_vector_table
	stcopr	r0, VBAR
	isb

	/* -----------------------------------------------------
	 * Enable the instruction cache
	 * -----------------------------------------------------
	 */
	ldcopr	r0, SCTLR
	orr	r0, r0, #SCTLR_I_BIT
	stcopr	r0, SCTLR
	isb

	/* ---------------------------------------------
	 * Since BL2 executes after BL1, it is assumed
	 * here that BL1 has already has done the
	 * necessary register initializations.
	 * ---------------------------------------------
	 */

	/* ---------------------------------------------
	 * Invalidate the RW memory used by the BL2
	 * image. This includes the data and NOBITS
	 * sections. This is done to safeguard against
	 * possible corruption of this memory by dirty
	 * cache lines in a system cache as a result of
	 * use by an earlier boot loader stage.
	 * ---------------------------------------------
	 */
	ldr	r0, =__RW_START__
	ldr	r1, =__RW_END__
	sub	r1, r1, r0
	bl	inv_dcache_range

	/* ---------------------------------------------
	 * Zero out NOBITS sections. There are 2 of them:
	 *   - the .bss section;
	 *   - the coherent memory section.
	 * ---------------------------------------------
	 */
	ldr	r0, =__BSS_START__
	ldr	r1, =__BSS_SIZE__
	bl	zeromem

#if USE_COHERENT_MEM
	ldr	r0, =__COHERENT_RAM_START__
	ldr	r1, =__COHERENT_RAM_UNALIGNED_SIZE__
	bl	zeromem
#endif

	/* --------------------------------------------
	 * Allocate a stack whose memory will be marked
	 * as Normal-IS-WBWA when the MMU is enabled.
	 * There is no risk of reading stale stack
	 * memory after enabling the MMU as only the
	 * primary cpu is running at the moment.
	 * --------------------------------------------
	 */
	bl	plat_set_my_stack

	/* ---------------------------------------------
	 * Initialize the stack protector canary before
	 * any C code is called.
	 * ---------------------------------------------
	 */
#if STACK_PROTECTOR_ENABLED
	bl	update_stack_protector_canary
#endif

	/* ---------------------------------------------
	 * Perform early platform setup & platform
	 * specific early arch. setup e.g. mmu setup
	 * ---------------------------------------------
	 */
	mov	r0, r11
	bl	bl2_early_platform_setup
	bl	bl2_plat_arch_setup

	/* ---------------------------------------------
	 * Jump to main function.
	 * ---------------------------------------------
	 */
	bl	bl2_main

	/* ---------------------------------------------
	 * Should never reach this point.
	 * ---------------------------------------------
	 */
	no_ret	plat_panic_handler

endfunc bl2_entrypoint