--- /dev/null
+/*
+ * Copyright (C) 2014-2016 Linaro Ltd. <ard.biesheuvel@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/elf.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/sort.h>
+
+struct plt_entry {
+ /*
+ * A program that conforms to the AArch64 Procedure Call Standard
+ * (AAPCS64) must assume that a veneer that alters IP0 (x16) and/or
+ * IP1 (x17) may be inserted at any branch instruction that is
+ * exposed to a relocation that supports long branches. Since that
+ * is exactly what we are dealing with here, we are free to use x16
+ * as a scratch register in the PLT veneers.
+ */
+ __le32 mov0; /* movn x16, #0x.... */
+ __le32 mov1; /* movk x16, #0x...., lsl #16 */
+ __le32 mov2; /* movk x16, #0x...., lsl #32 */
+ __le32 br; /* br x16 */
+};
+
+u64 module_emit_plt_entry(struct module *mod, const Elf64_Rela *rela,
+ Elf64_Sym *sym)
+{
+ struct plt_entry *plt = (struct plt_entry *)mod->arch.plt->sh_addr;
+ int i = mod->arch.plt_num_entries;
+ u64 val = sym->st_value + rela->r_addend;
+
+ /*
+ * We only emit PLT entries against undefined (SHN_UNDEF) symbols,
+ * which are listed in the ELF symtab section, but without a type
+ * or a size.
+ * So, similar to how the module loader uses the Elf64_Sym::st_value
+ * field to store the resolved addresses of undefined symbols, let's
+ * borrow the Elf64_Sym::st_size field (whose value is never used by
+ * the module loader, even for symbols that are defined) to record
+ * the address of a symbol's associated PLT entry as we emit it for a
+ * zero addend relocation (which is the only kind we have to deal with
+ * in practice). This allows us to find duplicates without having to
+ * go through the table every time.
+ */
+ if (rela->r_addend == 0 && sym->st_size != 0) {
+ BUG_ON(sym->st_size < (u64)plt || sym->st_size >= (u64)&plt[i]);
+ return sym->st_size;
+ }
+
+ mod->arch.plt_num_entries++;
+ BUG_ON(mod->arch.plt_num_entries > mod->arch.plt_max_entries);
+
+ /*
+ * MOVK/MOVN/MOVZ opcode:
+ * +--------+------------+--------+-----------+-------------+---------+
+ * | sf[31] | opc[30:29] | 100101 | hw[22:21] | imm16[20:5] | Rd[4:0] |
+ * +--------+------------+--------+-----------+-------------+---------+
+ *
+ * Rd := 0x10 (x16)
+ * hw := 0b00 (no shift), 0b01 (lsl #16), 0b10 (lsl #32)
+ * opc := 0b11 (MOVK), 0b00 (MOVN), 0b10 (MOVZ)
+ * sf := 1 (64-bit variant)
+ */
+ plt[i] = (struct plt_entry){
+ cpu_to_le32(0x92800010 | (((~val ) & 0xffff)) << 5),
+ cpu_to_le32(0xf2a00010 | ((( val >> 16) & 0xffff)) << 5),
+ cpu_to_le32(0xf2c00010 | ((( val >> 32) & 0xffff)) << 5),
+ cpu_to_le32(0xd61f0200)
+ };
+
+ if (rela->r_addend == 0)
+ sym->st_size = (u64)&plt[i];
+
+ return (u64)&plt[i];
+}
+
+#define cmp_3way(a,b) ((a) < (b) ? -1 : (a) > (b))
+
+static int cmp_rela(const void *a, const void *b)
+{
+ const Elf64_Rela *x = a, *y = b;
+ int i;
+
+ /* sort by type, symbol index and addend */
+ i = cmp_3way(ELF64_R_TYPE(x->r_info), ELF64_R_TYPE(y->r_info));
+ if (i == 0)
+ i = cmp_3way(ELF64_R_SYM(x->r_info), ELF64_R_SYM(y->r_info));
+ if (i == 0)
+ i = cmp_3way(x->r_addend, y->r_addend);
+ return i;
+}
+
+static bool duplicate_rel(const Elf64_Rela *rela, int num)
+{
+ /*
+ * Entries are sorted by type, symbol index and addend. That means
+ * that, if a duplicate entry exists, it must be in the preceding
+ * slot.
+ */
+ return num > 0 && cmp_rela(rela + num, rela + num - 1) == 0;
+}
+
+static unsigned int count_plts(Elf64_Sym *syms, Elf64_Rela *rela, int num)
+{
+ unsigned int ret = 0;
+ Elf64_Sym *s;
+ int i;
+
+ for (i = 0; i < num; i++) {
+ switch (ELF64_R_TYPE(rela[i].r_info)) {
+ case R_AARCH64_JUMP26:
+ case R_AARCH64_CALL26:
+ /*
+ * We only have to consider branch targets that resolve
+ * to undefined symbols. This is not simply a heuristic,
+ * it is a fundamental limitation, since the PLT itself
+ * is part of the module, and needs to be within 128 MB
+ * as well, so modules can never grow beyond that limit.
+ */
+ s = syms + ELF64_R_SYM(rela[i].r_info);
+ if (s->st_shndx != SHN_UNDEF)
+ break;
+
+ /*
+ * Jump relocations with non-zero addends against
+ * undefined symbols are supported by the ELF spec, but
+ * do not occur in practice (e.g., 'jump n bytes past
+ * the entry point of undefined function symbol f').
+ * So we need to support them, but there is no need to
+ * take them into consideration when trying to optimize
+ * this code. So let's only check for duplicates when
+ * the addend is zero: this allows us to record the PLT
+ * entry address in the symbol table itself, rather than
+ * having to search the list for duplicates each time we
+ * emit one.
+ */
+ if (rela[i].r_addend != 0 || !duplicate_rel(rela, i))
+ ret++;
+ break;
+ }
+ }
+ return ret;
+}
+
+int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
+ char *secstrings, struct module *mod)
+{
+ unsigned long plt_max_entries = 0;
+ Elf64_Sym *syms = NULL;
+ int i;
+
+ /*
+ * Find the empty .plt section so we can expand it to store the PLT
+ * entries. Record the symtab address as well.
+ */
+ for (i = 0; i < ehdr->e_shnum; i++) {
+ if (strcmp(".plt", secstrings + sechdrs[i].sh_name) == 0)
+ mod->arch.plt = sechdrs + i;
+ else if (sechdrs[i].sh_type == SHT_SYMTAB)
+ syms = (Elf64_Sym *)sechdrs[i].sh_addr;
+ }
+
+ if (!mod->arch.plt) {
+ pr_err("%s: module PLT section missing\n", mod->name);
+ return -ENOEXEC;
+ }
+ if (!syms) {
+ pr_err("%s: module symtab section missing\n", mod->name);
+ return -ENOEXEC;
+ }
+
+ for (i = 0; i < ehdr->e_shnum; i++) {
+ Elf64_Rela *rels = (void *)ehdr + sechdrs[i].sh_offset;
+ int numrels = sechdrs[i].sh_size / sizeof(Elf64_Rela);
+ Elf64_Shdr *dstsec = sechdrs + sechdrs[i].sh_info;
+
+ if (sechdrs[i].sh_type != SHT_RELA)
+ continue;
+
+ /* ignore relocations that operate on non-exec sections */
+ if (!(dstsec->sh_flags & SHF_EXECINSTR))
+ continue;
+
+ /* sort by type, symbol index and addend */
+ sort(rels, numrels, sizeof(Elf64_Rela), cmp_rela, NULL);
+
+ plt_max_entries += count_plts(syms, rels, numrels);
+ }
+
+ mod->arch.plt->sh_type = SHT_NOBITS;
+ mod->arch.plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
+ mod->arch.plt->sh_addralign = L1_CACHE_BYTES;
+ mod->arch.plt->sh_size = plt_max_entries * sizeof(struct plt_entry);
+ mod->arch.plt_num_entries = 0;
+ mod->arch.plt_max_entries = plt_max_entries;
+ return 0;
+}
GFP_KERNEL, PAGE_KERNEL_EXEC, 0,
NUMA_NO_NODE, __builtin_return_address(0));
+ if (!p && IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) &&
+ !IS_ENABLED(CONFIG_KASAN))
+ /*
+ * KASAN can only deal with module allocations being served
+ * from the reserved module region, since the remainder of
+ * the vmalloc region is already backed by zero shadow pages,
+ * and punching holes into it is non-trivial. Since the module
+ * region is not randomized when KASAN is enabled, it is even
+ * less likely that the module region gets exhausted, so we
+ * can simply omit this fallback in that case.
+ */
+ p = __vmalloc_node_range(size, MODULE_ALIGN, VMALLOC_START,
+ VMALLOC_END, GFP_KERNEL, PAGE_KERNEL_EXEC, 0,
+ NUMA_NO_NODE, __builtin_return_address(0));
+
if (p && (kasan_module_alloc(p, size) < 0)) {
vfree(p);
return NULL;
case R_AARCH64_CALL26:
ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 2, 26,
AARCH64_INSN_IMM_26);
+
+ if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) &&
+ ovf == -ERANGE) {
+ val = module_emit_plt_entry(me, &rel[i], sym);
+ ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 2,
+ 26, AARCH64_INSN_IMM_26);
+ }
break;
default:
projects / users / willy / pagecache.git / commitdiff