arch/arm/kernel/elf.c

   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
  10 int 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 }
  41 EXPORT_SYMBOL(elf_check_arch);
  42
  43 void 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 }
  78 EXPORT_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  *                 CPU: | lacks NX*  | has NX     |
  87  * ELF:                 |            |            |
  88  * ---------------------|------------|------------|
  89  * missing PT_GNU_STACK | exec-all   | exec-all   |
  90  * PT_GNU_STACK == RWX  | exec-all   | exec-stack |
  91  * PT_GNU_STACK == RW   | exec-all   | 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  */
 104 int 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 }
 112 EXPORT_SYMBOL(arm_elf_read_implies_exec);
 113
 114 #if defined(CONFIG_MMU) && defined(CONFIG_BINFMT_ELF_FDPIC)
 115
 116 void 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