arm/kernel/elf.c

0001 // SPDX-License-Identifier: GPL-2.0
0002 #include <linux/export.h>
0003 #include <linux/sched.h>
0004 #include <linux/personality.h>
0005 #include <linux/binfmts.h>
0006 #include <linux/elf.h>
0007 #include <linux/elf-fdpic.h>
0008 #include <asm/system_info.h>
0009
0010 int elf_check_arch(const struct elf32_hdr *x)
0011 {
0012     unsigned int eflags;
0013
0014     /* Make sure it's an ARM executable */
0015     if (x->e_machine != EM_ARM)
0016         return 0;
0017
0018     /* Make sure the entry address is reasonable */
0019     if (x->e_entry & 1) {
0020         if (!(elf_hwcap & HWCAP_THUMB))
0021             return 0;
0022     } else if (x->e_entry & 3)
0023         return 0;
0024
0025     eflags = x->e_flags;
0026     if ((eflags & EF_ARM_EABI_MASK) == EF_ARM_EABI_UNKNOWN) {
0027         unsigned int flt_fmt;
0028
0029         /* APCS26 is only allowed if the CPU supports it */
0030         if ((eflags & EF_ARM_APCS_26) && !(elf_hwcap & HWCAP_26BIT))
0031             return 0;
0032
0033         flt_fmt = eflags & (EF_ARM_VFP_FLOAT | EF_ARM_SOFT_FLOAT);
0034
0035         /* VFP requires the supporting code */
0036         if (flt_fmt == EF_ARM_VFP_FLOAT && !(elf_hwcap & HWCAP_VFP))
0037             return 0;
0038     }
0039     return 1;
0040 }
0041 EXPORT_SYMBOL(elf_check_arch);
0042
0043 void elf_set_personality(const struct elf32_hdr *x)
0044 {
0045     unsigned int eflags = x->e_flags;
0046     unsigned int personality = current->personality & ~PER_MASK;
0047
0048     /*
0049      * We only support Linux ELF executables, so always set the
0050      * personality to LINUX.
0051      */
0052     personality |= PER_LINUX;
0053
0054     /*
0055      * APCS-26 is only valid for OABI executables
0056      */
0057     if ((eflags & EF_ARM_EABI_MASK) == EF_ARM_EABI_UNKNOWN &&
0058         (eflags & EF_ARM_APCS_26))
0059         personality &= ~ADDR_LIMIT_32BIT;
0060     else
0061         personality |= ADDR_LIMIT_32BIT;
0062
0063     set_personality(personality);
0064
0065     /*
0066      * Since the FPA coprocessor uses CP1 and CP2, and iWMMXt uses CP0
0067      * and CP1, we only enable access to the iWMMXt coprocessor if the
0068      * binary is EABI or softfloat (and thus, guaranteed not to use
0069      * FPA instructions.)
0070      */
0071     if (elf_hwcap & HWCAP_IWMMXT &&
0072         eflags & (EF_ARM_EABI_MASK | EF_ARM_SOFT_FLOAT)) {
0073         set_thread_flag(TIF_USING_IWMMXT);
0074     } else {
0075         clear_thread_flag(TIF_USING_IWMMXT);
0076     }
0077 }
0078 EXPORT_SYMBOL(elf_set_personality);
0079
0080 /*
0081  * An executable for which elf_read_implies_exec() returns TRUE will
0082  * have the READ_IMPLIES_EXEC personality flag set automatically.
0083  *
0084  * The decision process for determining the results are:
0085  *
0086  *                 CPU: | lacks NX*  | has NX     |
0087  * ELF:                 |            |            |
0088  * ---------------------|------------|------------|
0089  * missing PT_GNU_STACK | exec-all   | exec-all   |
0090  * PT_GNU_STACK == RWX  | exec-all   | exec-stack |
0091  * PT_GNU_STACK == RW   | exec-all   | exec-none  |
0092  *
0093  *  exec-all  : all PROT_READ user mappings are executable, except when
0094  *              backed by files on a noexec-filesystem.
0095  *  exec-none : only PROT_EXEC user mappings are executable.
0096  *  exec-stack: only the stack and PROT_EXEC user mappings are executable.
0097  *
0098  *  *this column has no architectural effect: NX markings are ignored by
0099  *   hardware, but may have behavioral effects when "wants X" collides with
0100  *   "cannot be X" constraints in memory permission flags, as in
0101  *   https://lkml.kernel.org/r/20190418055759.GA3155@mellanox.com
0102  *
0103  */
0104 int arm_elf_read_implies_exec(int executable_stack)
0105 {
0106     if (executable_stack == EXSTACK_DEFAULT)
0107         return 1;
0108     if (cpu_architecture() < CPU_ARCH_ARMv6)
0109         return 1;
0110     return 0;
0111 }
0112 EXPORT_SYMBOL(arm_elf_read_implies_exec);
0113
0114 #if defined(CONFIG_MMU) && defined(CONFIG_BINFMT_ELF_FDPIC)
0115
0116 void elf_fdpic_arch_lay_out_mm(struct elf_fdpic_params *exec_params,
0117                    struct elf_fdpic_params *interp_params,
0118                    unsigned long *start_stack,
0119                    unsigned long *start_brk)
0120 {
0121     elf_set_personality(&exec_params->hdr);
0122
0123     exec_params->load_addr = 0x8000;
0124     interp_params->load_addr = ELF_ET_DYN_BASE;
0125     *start_stack = TASK_SIZE - SZ_16M;
0126
0127     if ((exec_params->flags & ELF_FDPIC_FLAG_ARRANGEMENT) == ELF_FDPIC_FLAG_INDEPENDENT) {
0128         exec_params->flags &= ~ELF_FDPIC_FLAG_ARRANGEMENT;
0129         exec_params->flags |= ELF_FDPIC_FLAG_CONSTDISP;
0130     }
0131 }
0132
0133 #endif