xref: /openbmc/linux/arch/arm/kernel/elf.c (revision eaf3f9e6)
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 
elf_check_arch(const struct elf32_hdr * x)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 
elf_set_personality(const struct elf32_hdr * x)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  */
arm_elf_read_implies_exec(int executable_stack)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 
elf_fdpic_arch_lay_out_mm(struct elf_fdpic_params * exec_params,struct elf_fdpic_params * interp_params,unsigned long * start_stack,unsigned long * start_brk)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
134