source: mainline/uspace/lib/c/generic/elf/elf_mod.c@ 64d38cd

/*
 * Copyright (c) 2006 Sergey Bondari
 * Copyright (c) 2006 Jakub Jermar
 * Copyright (c) 2011 Jiri Svoboda
 * 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.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
 */

/** @addtogroup generic
 * @{
 */

/**
 * @file
 * @brief       Userspace ELF module loader.
 *
 * This module allows loading ELF binaries (both executables and
 * shared objects) from VFS. The current implementation allocates
 * anonymous memory, fills it with segment data and then adjusts
 * the memory areas' flags to the final value. In the future,
 * the segments will be mapped directly from the file.
 */

#include <errno.h>
#include <stdio.h>
#include <vfs/vfs.h>
#include <stddef.h>
#include <stdint.h>
#include <align.h>
#include <assert.h>
#include <as.h>
#include <elf/elf.h>
#include <smc.h>
#include <loader/pcb.h>
#include <entry_point.h>
#include <str_error.h>
#include <stdlib.h>
#include <macros.h>

#include <elf/elf_load.h>

#define DPRINTF(...)

static const char *error_codes[] = {
        "no error",
        "invalid image",
        "address space error",
        "incompatible image",
        "unsupported image type",
        "irrecoverable error",
        "file io error"
};

static unsigned int elf_load_module(elf_ld_t *elf);
static int load_segment(elf_ld_t *elf, elf_segment_header_t *entry);

/** Load ELF binary from a file.
 *
 * Load an ELF binary from the specified file. If the file is
 * an executable program, it is loaded unbiased. If it is a shared
 * object, it is loaded with the bias @a so_bias. Some information
 * extracted from the binary is stored in a elf_info_t structure
 * pointed to by @a info.
 *
 * @param file      ELF file.
 * @param info      Pointer to a structure for storing information
 *                  extracted from the binary.
 *
 * @return EE_OK on success or EE_xx error code.
 *
 */
int elf_load_file(int file, eld_flags_t flags, elf_finfo_t *info)
{
        elf_ld_t elf;

        int ofile;
        errno_t rc = vfs_clone(file, -1, true, &ofile);
        if (rc == EOK) {
                rc = vfs_open(ofile, MODE_READ);
        }
        if (rc != EOK) {
                return EE_IO;
        }

        elf.fd = ofile;
        elf.info = info;
        elf.flags = flags;

        int ret = elf_load_module(&elf);

        vfs_put(ofile);
        return ret;
}

int elf_load_file_name(const char *path, eld_flags_t flags, elf_finfo_t *info)
{
        int file;
        errno_t rc = vfs_lookup(path, 0, &file);
        if (rc == EOK) {
                int ret = elf_load_file(file, flags, info);
                vfs_put(file);
                return ret;
        } else {
                return EE_IO;
        }
}

/** Process TLS program header.
 *
 * @param elf  Pointer to loader state buffer.
 * @param hdr  TLS program header
 * @param info Place to store TLS info
 */
static void tls_program_header(void *base, elf_tls_info_t *info)
{
        const elf_segment_header_t *tls = elf_get_phdr(base, PT_TLS);
        size_t bias = elf_get_bias(base);

        if (tls == NULL) {
                /* Ensure valid TLS info even if there is no TLS header. */
                info->tdata = NULL;
                info->tdata_size = 0;
                info->tbss_size = 0;
                info->tls_align = 1;
        } else {
                info->tdata = (void *) tls->p_vaddr + bias;
                info->tdata_size = tls->p_filesz;
                info->tbss_size = tls->p_memsz - tls->p_filesz;
                info->tls_align = tls->p_align;
        }
}

/** Load an ELF binary.
 *
 * The @a elf structure contains the loader state, including
 * an open file, from which the binary will be loaded,
 * a pointer to the @c info structure etc.
 *
 * @param elf           Pointer to loader state buffer.
 * @return EE_OK on success or EE_xx error code.
 */
static unsigned int elf_load_module(elf_ld_t *elf)
{
        elf_header_t header_buf;
        elf_header_t *header = &header_buf;
        aoff64_t pos = 0;
        size_t nr;
        int i, ret;
        errno_t rc;

        rc = vfs_read(elf->fd, &pos, header, sizeof(elf_header_t), &nr);
        if (rc != EOK || nr != sizeof(elf_header_t)) {
                DPRINTF("Read error.\n");
                return EE_IO;
        }

        /* Identify ELF */
        if (header->e_ident[EI_MAG0] != ELFMAG0 ||
            header->e_ident[EI_MAG1] != ELFMAG1 ||
            header->e_ident[EI_MAG2] != ELFMAG2 ||
            header->e_ident[EI_MAG3] != ELFMAG3) {
                DPRINTF("Invalid header.\n");
                return EE_INVALID;
        }

        /* Identify ELF compatibility */
        if (header->e_ident[EI_DATA] != ELF_DATA_ENCODING ||
            header->e_machine != ELF_MACHINE ||
            header->e_ident[EI_VERSION] != EV_CURRENT ||
            header->e_version != EV_CURRENT ||
            header->e_ident[EI_CLASS] != ELF_CLASS) {
                DPRINTF("Incompatible data/version/class.\n");
                return EE_INCOMPATIBLE;
        }

        if (header->e_phentsize != sizeof(elf_segment_header_t)) {
                DPRINTF("e_phentsize: %u != %zu\n", header->e_phentsize,
                    sizeof(elf_segment_header_t));
                return EE_INCOMPATIBLE;
        }

        /* Check if the object type is supported. */
        if (header->e_type != ET_EXEC && header->e_type != ET_DYN) {
                DPRINTF("Object type %d is not supported\n", header->e_type);
                return EE_UNSUPPORTED;
        }

        if (header->e_phoff == 0) {
                DPRINTF("Program header table is not present!\n");
                return EE_INCOMPATIBLE;
        }

        /* Read program header table.
         * Normally, there is very few program headers, so don't bother
         * with allocating memory dynamically.
         */
        const int phdr_cap = 16;
        elf_segment_header_t phdr[phdr_cap];
        size_t phdr_len = header->e_phnum * header->e_phentsize;

        if (phdr_len > sizeof(phdr)) {
                DPRINTF("more than %d program headers\n", phdr_cap);
                return EE_UNSUPPORTED;
        }

        pos = header->e_phoff;
        rc = vfs_read(elf->fd, &pos, phdr, phdr_len, &nr);
        if (rc != EOK || nr != phdr_len) {
                DPRINTF("Read error.\n");
                return EE_IO;
        }

        uintptr_t module_base = UINTPTR_MAX;
        uintptr_t module_top = 0;
        uintptr_t base_offset = UINTPTR_MAX;

        /* Walk through PT_LOAD headers, to find out the size of the module. */
        for (i = 0; i < header->e_phnum; i++) {
                if (phdr[i].p_type != PT_LOAD)
                        continue;

                if (module_base > phdr[i].p_vaddr) {
                        module_base = phdr[i].p_vaddr;
                        base_offset = phdr[i].p_offset;
                }
                module_top = max(module_top, phdr[i].p_vaddr + phdr[i].p_memsz);
        }

        if (base_offset != 0) {
                DPRINTF("ELF headers not present in the text segment.\n");
                return EE_INVALID;
        }

        /* Shared objects can be loaded with a bias */
        if (header->e_type != ET_DYN) {
                elf->bias = 0;
        } else {
                if (module_base != 0) {
                        DPRINTF("Unexpected shared object format.\n");
                        return EE_INVALID;
                }

                /* Attempt to allocate a span of memory large enough for the
                 * shared object.
                 */
                // FIXME: This is not reliable when we're running
                //        multi-threaded. Even if this part succeeds, later
                //        allocation can fail because another thread took the
                //        space in the meantime. This is only relevant for
                //        dlopen() though.
                void *area = as_area_create(AS_AREA_ANY, module_top,
                    AS_AREA_READ | AS_AREA_WRITE | AS_AREA_CACHEABLE |
                    AS_AREA_LATE_RESERVE, AS_AREA_UNPAGED);

                if (area == AS_MAP_FAILED) {
                        DPRINTF("Can't find suitable memory area.\n");
                        return EE_MEMORY;
                }

                elf->bias = (uintptr_t) area;
                as_area_destroy(area);
        }

        /* Load all loadable segments. */
        for (i = 0; i < header->e_phnum; i++) {
                if (phdr[i].p_type != PT_LOAD)
                        continue;

                ret = load_segment(elf, &phdr[i]);
                if (ret != EE_OK)
                        return ret;
        }

        void *base = (void *) module_base + elf->bias;
        elf->info->base = base;

        /* Handle TLS. */
        tls_program_header(base, &elf->info->tls);

        /* Handle PT_INTERP. */

        const elf_segment_header_t *interphdr = elf_get_phdr(base, PT_INTERP);

        if (interphdr == NULL) {
                interphdr = NULL;
        } else {
                elf->info->interp =
                    (const char *) (interphdr->p_vaddr + elf->bias);
                if (elf->info->interp[interphdr->p_filesz - 1] != '\0') {
                        DPRINTF("Unterminated ELF interp string.\n");
                        elf->info->interp = NULL;
                } else {
                        DPRINTF("interpreter: \"%s\"\n", elf->info->interp);
                }
        }

        /* Handle PT_DYNAMIC. */

        const elf_segment_header_t *dynphdr = elf_get_phdr(base, PT_DYNAMIC);

        if (dynphdr == NULL) {
                elf->info->dynamic = NULL;
        } else {
                /* Record pointer to dynamic section into info structure */
                elf->info->dynamic = (void *) (dynphdr->p_vaddr + elf->bias);
                DPRINTF("dynamic section found at %p\n",
                    (void *)elf->info->dynamic);
        }

        elf->info->entry =
            (entry_point_t)((uint8_t *)header->e_entry + elf->bias);

        DPRINTF("Done.\n");

        return EE_OK;
}

/** Print error message according to error code.
 *
 * @param rc Return code returned by elf_load().
 *
 * @return NULL terminated description of error.
 */
const char *elf_error(unsigned int rc)
{
        assert(rc < sizeof(error_codes) / sizeof(char *));

        return error_codes[rc];
}

/** Load segment described by program header entry.
 *
 * @param elf   Loader state.
 * @param entry Program header entry describing segment to be loaded.
 *
 * @return EE_OK on success, error code otherwise.
 */
int load_segment(elf_ld_t *elf, elf_segment_header_t *entry)
{
        void *a;
        int flags = 0;
        uintptr_t bias;
        uintptr_t base;
        void *seg_ptr;
        uintptr_t seg_addr;
        size_t mem_sz;
        aoff64_t pos;
        errno_t rc;
        size_t nr;

        bias = elf->bias;

        seg_addr = entry->p_vaddr + bias;
        seg_ptr = (void *) seg_addr;

        DPRINTF("Load segment at addr %p, size 0x%zx\n", (void *) seg_addr,
            entry->p_memsz);

        if (entry->p_align > 1) {
                if ((entry->p_offset % entry->p_align) !=
                    (seg_addr % entry->p_align)) {
                        DPRINTF("Align check 1 failed offset%%align=0x%zx, "
                            "vaddr%%align=0x%zx\n",
                            entry->p_offset % entry->p_align,
                            seg_addr % entry->p_align);
                        return EE_INVALID;
                }
        }

        /* Final flags that will be set for the memory area */

        if (entry->p_flags & PF_X)
                flags |= AS_AREA_EXEC;
        if (entry->p_flags & PF_W)
                flags |= AS_AREA_WRITE;
        if (entry->p_flags & PF_R)
                flags |= AS_AREA_READ;
        flags |= AS_AREA_CACHEABLE;

        base = ALIGN_DOWN(entry->p_vaddr, PAGE_SIZE);
        mem_sz = entry->p_memsz + (entry->p_vaddr - base);

        DPRINTF("Map to seg_addr=%p-%p.\n", (void *) seg_addr,
            (void *) (entry->p_vaddr + bias +
            ALIGN_UP(entry->p_memsz, PAGE_SIZE)));

        /*
         * For the course of loading, the area needs to be readable
         * and writeable.
         */
        a = as_area_create((uint8_t *) base + bias, mem_sz,
            AS_AREA_READ | AS_AREA_WRITE | AS_AREA_CACHEABLE,
            AS_AREA_UNPAGED);
        if (a == AS_MAP_FAILED) {
                DPRINTF("memory mapping failed (%p, %zu)\n",
                    (void *) (base + bias), mem_sz);
                return EE_MEMORY;
        }

        DPRINTF("as_area_create(%p, %#zx, %d) -> %p\n",
            (void *) (base + bias), mem_sz, flags, (void *) a);

        /*
         * Load segment data
         */
        pos = entry->p_offset;
        rc = vfs_read(elf->fd, &pos, seg_ptr, entry->p_filesz, &nr);
        if (rc != EOK || nr != entry->p_filesz) {
                DPRINTF("read error\n");
                return EE_IO;
        }

        /*
         * The caller wants to modify the segments first. He will then
         * need to set the right access mode and ensure SMC coherence.
         */
        if ((elf->flags & ELDF_RW) != 0)
                return EE_OK;

        rc = as_area_change_flags(seg_ptr, flags);
        if (rc != EOK) {
                DPRINTF("Failed to set memory area flags.\n");
                return EE_MEMORY;
        }

        if (flags & AS_AREA_EXEC) {
                /* Enforce SMC coherence for the segment */
                if (smc_coherence(seg_ptr, entry->p_filesz))
                        return EE_MEMORY;
        }

        return EE_OK;
}

/** @}
 */