• Soby Mathew's avatar
    PIE: Position Independant Executable support for BL31 · 931f7c61
    Soby Mathew authored
    
    This patch introduces Position Independant Executable(PIE) support
    in TF-A. As a initial prototype, only BL31 can support PIE. A trivial
    dynamic linker is implemented which supports fixing up Global Offset
    Table(GOT) and Dynamic relocations(.rela.dyn). The fixup_gdt_reloc()
    helper function implements this linker and this needs to be called
    early in the boot sequence prior to invoking C functions. The GOT is
    placed in the RO section of BL31 binary for improved security and the
    BL31 linker script is modified to export the appropriate symbols
    required for the dynamic linker.
    
    The C compiler always generates PC relative addresses to linker symbols
    and hence referencing symbols exporting constants are a problem when
    relocating the binary. Hence the reference to the
    `__PERCPU_TIMESTAMP_SIZE__` symbol in PMF is removed and is now calculated
    at runtime based on start and end addresses.
    
    Change-Id: I1228583ff92cf432963b7cef052e95d995cca93d
    Signed-off-by: default avatarSoby Mathew <soby.mathew@arm.com>
    931f7c61
bl31.ld.S 8.45 KB
/*
 * Copyright (c) 2013-2018, ARM Limited and Contributors. All rights reserved.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

#include <platform_def.h>
#include <xlat_tables_defs.h>

OUTPUT_FORMAT(PLATFORM_LINKER_FORMAT)
OUTPUT_ARCH(PLATFORM_LINKER_ARCH)
ENTRY(bl31_entrypoint)


MEMORY {
    RAM (rwx): ORIGIN = BL31_BASE, LENGTH = BL31_LIMIT - BL31_BASE
}

#ifdef PLAT_EXTRA_LD_SCRIPT
#include <plat.ld.S>
#endif

SECTIONS
{
    . = BL31_BASE;
    ASSERT(. == ALIGN(PAGE_SIZE),
           "BL31_BASE address is not aligned on a page boundary.")

    __BL31_START__ = .;

#if SEPARATE_CODE_AND_RODATA
    .text . : {
        __TEXT_START__ = .;
        *bl31_entrypoint.o(.text*)
        *(.text*)
        *(.vectors)
        . = ALIGN(PAGE_SIZE);
        __TEXT_END__ = .;
    } >RAM

    .rodata . : {
        __RODATA_START__ = .;
        *(.rodata*)

        /* Ensure 8-byte alignment for descriptors and ensure inclusion */
        . = ALIGN(8);
        __RT_SVC_DESCS_START__ = .;
        KEEP(*(rt_svc_descs))
        __RT_SVC_DESCS_END__ = .;

#if ENABLE_PMF
        /* Ensure 8-byte alignment for descriptors and ensure inclusion */
        . = ALIGN(8);
        __PMF_SVC_DESCS_START__ = .;
        KEEP(*(pmf_svc_descs))
        __PMF_SVC_DESCS_END__ = .;
#endif /* ENABLE_PMF */

        /*
         * Ensure 8-byte alignment for cpu_ops so that its fields are also
         * aligned. Also ensure cpu_ops inclusion.
         */
        . = ALIGN(8);
        __CPU_OPS_START__ = .;
        KEEP(*(cpu_ops))
        __CPU_OPS_END__ = .;

        /*
         * Keep the .got section in the RO section as the it is patched
         * prior to enabling the MMU and having the .got in RO is better for
         * security.
         */
        . = ALIGN(16);
        __GOT_START__ = .;
        *(.got)
        __GOT_END__ = .;

        /* Place pubsub sections for events */
        . = ALIGN(8);
#include <pubsub_events.h>

        . = ALIGN(PAGE_SIZE);
        __RODATA_END__ = .;
    } >RAM
#else
    ro . : {
        __RO_START__ = .;
        *bl31_entrypoint.o(.text*)
        *(.text*)
        *(.rodata*)

        /* Ensure 8-byte alignment for descriptors and ensure inclusion */
        . = ALIGN(8);
        __RT_SVC_DESCS_START__ = .;
        KEEP(*(rt_svc_descs))
        __RT_SVC_DESCS_END__ = .;

#if ENABLE_PMF
        /* Ensure 8-byte alignment for descriptors and ensure inclusion */
        . = ALIGN(8);
        __PMF_SVC_DESCS_START__ = .;
        KEEP(*(pmf_svc_descs))
        __PMF_SVC_DESCS_END__ = .;
#endif /* ENABLE_PMF */

        /*
         * Ensure 8-byte alignment for cpu_ops so that its fields are also
         * aligned. Also ensure cpu_ops inclusion.
         */
        . = ALIGN(8);
        __CPU_OPS_START__ = .;
        KEEP(*(cpu_ops))
        __CPU_OPS_END__ = .;

        /* Place pubsub sections for events */
        . = ALIGN(8);
#include <pubsub_events.h>

        *(.vectors)
        __RO_END_UNALIGNED__ = .;
        /*
         * Memory page(s) mapped to this section will be marked as read-only,
         * executable.  No RW data from the next section must creep in.
         * Ensure the rest of the current memory page is unused.
         */
        . = ALIGN(PAGE_SIZE);
        __RO_END__ = .;
    } >RAM
#endif

    ASSERT(__CPU_OPS_END__ > __CPU_OPS_START__,
           "cpu_ops not defined for this platform.")

#if ENABLE_SPM
    /*
     * Exception vectors of the SPM shim layer. They must be aligned to a 2K
     * address, but we need to place them in a separate page so that we can set
     * individual permissions to them, so the actual alignment needed is 4K.
     *
     * There's no need to include this into the RO section of BL31 because it
     * doesn't need to be accessed by BL31.
     */
    spm_shim_exceptions : ALIGN(PAGE_SIZE) {
        __SPM_SHIM_EXCEPTIONS_START__ = .;
        *(.spm_shim_exceptions)
        . = ALIGN(PAGE_SIZE);
        __SPM_SHIM_EXCEPTIONS_END__ = .;
    } >RAM
#endif

    /*
     * Define a linker symbol to mark start of the RW memory area for this
     * image.
     */
    __RW_START__ = . ;

    /*
     * .data must be placed at a lower address than the stacks if the stack
     * protector is enabled. Alternatively, the .data.stack_protector_canary
     * section can be placed independently of the main .data section.
     */
   .data . : {
        __DATA_START__ = .;
        *(.data*)
        __DATA_END__ = .;
    } >RAM

    . = ALIGN(16);
    /*
     * .rela.dyn needs to come after .data for the read-elf utility to parse
     * this section correctly.
     */
    __RELA_START__ = .;
    .rela.dyn . : {
    } >RAM
    __RELA_END__ = .;

#ifdef BL31_PROGBITS_LIMIT
    ASSERT(. <= BL31_PROGBITS_LIMIT, "BL31 progbits has exceeded its limit.")
#endif

    stacks (NOLOAD) : {
        __STACKS_START__ = .;
        *(tzfw_normal_stacks)
        __STACKS_END__ = .;
    } >RAM

    /*
     * The .bss section gets initialised to 0 at runtime.
     * Its base address should be 16-byte aligned for better performance of the
     * zero-initialization code.
     */
    .bss (NOLOAD) : ALIGN(16) {
        __BSS_START__ = .;
        *(.bss*)
        *(COMMON)
#if !USE_COHERENT_MEM
        /*
         * Bakery locks are stored in normal .bss memory
         *
         * Each lock's data is spread across multiple cache lines, one per CPU,
         * but multiple locks can share the same cache line.
         * The compiler will allocate enough memory for one CPU's bakery locks,
         * the remaining cache lines are allocated by the linker script
         */
        . = ALIGN(CACHE_WRITEBACK_GRANULE);
        __BAKERY_LOCK_START__ = .;
        *(bakery_lock)
        . = ALIGN(CACHE_WRITEBACK_GRANULE);
        __PERCPU_BAKERY_LOCK_SIZE__ = ABSOLUTE(. - __BAKERY_LOCK_START__);
        . = . + (__PERCPU_BAKERY_LOCK_SIZE__ * (PLATFORM_CORE_COUNT - 1));
        __BAKERY_LOCK_END__ = .;

	/*
	 * If BL31 doesn't use any bakery lock then __PERCPU_BAKERY_LOCK_SIZE__
	 * will be zero. For this reason, the only two valid values for
	 * __PERCPU_BAKERY_LOCK_SIZE__ are 0 or the platform defined value
	 * PLAT_PERCPU_BAKERY_LOCK_SIZE.
	 */
#ifdef PLAT_PERCPU_BAKERY_LOCK_SIZE
    ASSERT((__PERCPU_BAKERY_LOCK_SIZE__ == 0) || (__PERCPU_BAKERY_LOCK_SIZE__ == PLAT_PERCPU_BAKERY_LOCK_SIZE),
        "PLAT_PERCPU_BAKERY_LOCK_SIZE does not match bakery lock requirements");
#endif
#endif

#if ENABLE_PMF
        /*
         * Time-stamps are stored in normal .bss memory
         *
         * The compiler will allocate enough memory for one CPU's time-stamps,
         * the remaining memory for other CPU's is allocated by the
         * linker script
         */
        . = ALIGN(CACHE_WRITEBACK_GRANULE);
        __PMF_TIMESTAMP_START__ = .;
        KEEP(*(pmf_timestamp_array))
        . = ALIGN(CACHE_WRITEBACK_GRANULE);
        __PMF_PERCPU_TIMESTAMP_END__ = .;
        __PERCPU_TIMESTAMP_SIZE__ = ABSOLUTE(. - __PMF_TIMESTAMP_START__);
        . = . + (__PERCPU_TIMESTAMP_SIZE__ * (PLATFORM_CORE_COUNT - 1));
        __PMF_TIMESTAMP_END__ = .;
#endif /* ENABLE_PMF */
        __BSS_END__ = .;
    } >RAM

    /*
     * The xlat_table section is for full, aligned page tables (4K).
     * Removing them from .bss avoids forcing 4K alignment on
     * the .bss section. The tables are initialized to zero by the translation
     * tables library.
     */
    xlat_table (NOLOAD) : {
        *(xlat_table)
    } >RAM

#if USE_COHERENT_MEM
    /*
     * The base address of the coherent memory section must be page-aligned (4K)
     * to guarantee that the coherent data are stored on their own pages and
     * are not mixed with normal data.  This is required to set up the correct
     * memory attributes for the coherent data page tables.
     */
    coherent_ram (NOLOAD) : ALIGN(PAGE_SIZE) {
        __COHERENT_RAM_START__ = .;
        /*
         * Bakery locks are stored in coherent memory
         *
         * Each lock's data is contiguous and fully allocated by the compiler
         */
        *(bakery_lock)
        *(tzfw_coherent_mem)
        __COHERENT_RAM_END_UNALIGNED__ = .;
        /*
         * Memory page(s) mapped to this section will be marked
         * as device memory.  No other unexpected data must creep in.
         * Ensure the rest of the current memory page is unused.
         */
        . = ALIGN(PAGE_SIZE);
        __COHERENT_RAM_END__ = .;
    } >RAM
#endif

    /*
     * Define a linker symbol to mark end of the RW memory area for this
     * image.
     */
    __RW_END__ = .;
    __BL31_END__ = .;

    ASSERT(. <= BL31_LIMIT, "BL31 image has exceeded its limit.")
}