linux/arch/arm/kernel/elf.c
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   1// SPDX-License-Identifier: GPL-2.0
   2#include <linux/export.h>
   3#include <linux/sched.h>
   4#include <linux/personality.h>
   5#include <linux/binfmts.h>
   6#include <linux/elf.h>
   7#include <linux/elf-fdpic.h>
   8#include <asm/system_info.h>
   9
  10int elf_check_arch(const struct elf32_hdr *x)
  11{
  12        unsigned int eflags;
  13
  14        /* Make sure it's an ARM executable */
  15        if (x->e_machine != EM_ARM)
  16                return 0;
  17
  18        /* Make sure the entry address is reasonable */
  19        if (x->e_entry & 1) {
  20                if (!(elf_hwcap & HWCAP_THUMB))
  21                        return 0;
  22        } else if (x->e_entry & 3)
  23                return 0;
  24
  25        eflags = x->e_flags;
  26        if ((eflags & EF_ARM_EABI_MASK) == EF_ARM_EABI_UNKNOWN) {
  27                unsigned int flt_fmt;
  28
  29                /* APCS26 is only allowed if the CPU supports it */
  30                if ((eflags & EF_ARM_APCS_26) && !(elf_hwcap & HWCAP_26BIT))
  31                        return 0;
  32
  33                flt_fmt = eflags & (EF_ARM_VFP_FLOAT | EF_ARM_SOFT_FLOAT);
  34
  35                /* VFP requires the supporting code */
  36                if (flt_fmt == EF_ARM_VFP_FLOAT && !(elf_hwcap & HWCAP_VFP))
  37                        return 0;
  38        }
  39        return 1;
  40}
  41EXPORT_SYMBOL(elf_check_arch);
  42
  43void elf_set_personality(const struct elf32_hdr *x)
  44{
  45        unsigned int eflags = x->e_flags;
  46        unsigned int personality = current->personality & ~PER_MASK;
  47
  48        /*
  49         * We only support Linux ELF executables, so always set the
  50         * personality to LINUX.
  51         */
  52        personality |= PER_LINUX;
  53
  54        /*
  55         * APCS-26 is only valid for OABI executables
  56         */
  57        if ((eflags & EF_ARM_EABI_MASK) == EF_ARM_EABI_UNKNOWN &&
  58            (eflags & EF_ARM_APCS_26))
  59                personality &= ~ADDR_LIMIT_32BIT;
  60        else
  61                personality |= ADDR_LIMIT_32BIT;
  62
  63        set_personality(personality);
  64
  65        /*
  66         * Since the FPA coprocessor uses CP1 and CP2, and iWMMXt uses CP0
  67         * and CP1, we only enable access to the iWMMXt coprocessor if the
  68         * binary is EABI or softfloat (and thus, guaranteed not to use
  69         * FPA instructions.)
  70         */
  71        if (elf_hwcap & HWCAP_IWMMXT &&
  72            eflags & (EF_ARM_EABI_MASK | EF_ARM_SOFT_FLOAT)) {
  73                set_thread_flag(TIF_USING_IWMMXT);
  74        } else {
  75                clear_thread_flag(TIF_USING_IWMMXT);
  76        }
  77}
  78EXPORT_SYMBOL(elf_set_personality);
  79
  80/*
  81 * An executable for which elf_read_implies_exec() returns TRUE will
  82 * have the READ_IMPLIES_EXEC personality flag set automatically.
  83 *
  84 * The decision process for determining the results are:
  85 *
  86 * \xC2\xA0 \xC2\xA0 \xC2\xA0 \xC2\xA0 \xC2\xA0 \xC2\xA0    \xC2\xA0CPU: | lacks NX* \xC2\xA0| has NX     |
  87 * ELF: \xC2\xA0 \xC2\xA0 \xC2\xA0 \xC2\xA0    \xC2\xA0 \xC2\xA0 \xC2\xA0| \xC2\xA0 \xC2\xA0 \xC2\xA0 \xC2\xA0 \xC2\xA0 \xC2\xA0| \xC2\xA0 \xC2\xA0 \xC2\xA0 \xC2\xA0 \xC2\xA0  |
  88 * ---------------------|------------|------------|
  89 * missing PT_GNU_STACK | exec-all \xC2\xA0 | exec-all  \xC2\xA0|
  90 * PT_GNU_STACK == RWX \xC2\xA0| exec-all \xC2\xA0 | exec-stack\xC2\xA0|
  91 * PT_GNU_STACK == RW \xC2\xA0 | exec-all  \xC2\xA0| exec-none  |
  92 *
  93 *  exec-all  : all PROT_READ user mappings are executable, except when
  94 *              backed by files on a noexec-filesystem.
  95 *  exec-none : only PROT_EXEC user mappings are executable.
  96 *  exec-stack: only the stack and PROT_EXEC user mappings are executable.
  97 *
  98 *  *this column has no architectural effect: NX markings are ignored by
  99 *   hardware, but may have behavioral effects when "wants X" collides with
 100 *   "cannot be X" constraints in memory permission flags, as in
 101 *   https://lkml.kernel.org/r/20190418055759.GA3155@mellanox.com
 102 *
 103 */
 104int arm_elf_read_implies_exec(int executable_stack)
 105{
 106        if (executable_stack == EXSTACK_DEFAULT)
 107                return 1;
 108        if (cpu_architecture() < CPU_ARCH_ARMv6)
 109                return 1;
 110        return 0;
 111}
 112EXPORT_SYMBOL(arm_elf_read_implies_exec);
 113
 114#if defined(CONFIG_MMU) && defined(CONFIG_BINFMT_ELF_FDPIC)
 115
 116void elf_fdpic_arch_lay_out_mm(struct elf_fdpic_params *exec_params,
 117                               struct elf_fdpic_params *interp_params,
 118                               unsigned long *start_stack,
 119                               unsigned long *start_brk)
 120{
 121        elf_set_personality(&exec_params->hdr);
 122
 123        exec_params->load_addr = 0x8000;
 124        interp_params->load_addr = ELF_ET_DYN_BASE;
 125        *start_stack = TASK_SIZE - SZ_16M;
 126
 127        if ((exec_params->flags & ELF_FDPIC_FLAG_ARRANGEMENT) == ELF_FDPIC_FLAG_INDEPENDENT) {
 128                exec_params->flags &= ~ELF_FDPIC_FLAG_ARRANGEMENT;
 129                exec_params->flags |= ELF_FDPIC_FLAG_CONSTDISP;
 130        }
 131}
 132
 133#endif
 134