1 files changed, 378 insertions, 0 deletions

diff --git a/arch/arm64/kernel/module-plts.c b/arch/arm64/kernel/module-plts.c
new file mode 100644
index 000000000..29569284f
--- /dev/null
+++ b/arch/arm64/kernel/module-plts.c
@@ -0,0 +1,378 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2014-2017 Linaro Ltd. <ard.biesheuvel@linaro.org>
+ */
+
+#include <linux/elf.h>
+#include <linux/ftrace.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/moduleloader.h>
+#include <linux/sort.h>
+
+static struct plt_entry __get_adrp_add_pair(u64 dst, u64 pc,
+					    enum aarch64_insn_register reg)
+{
+	u32 adrp, add;
+
+	adrp = aarch64_insn_gen_adr(pc, dst, reg, AARCH64_INSN_ADR_TYPE_ADRP);
+	add = aarch64_insn_gen_add_sub_imm(reg, reg, dst % SZ_4K,
+					   AARCH64_INSN_VARIANT_64BIT,
+					   AARCH64_INSN_ADSB_ADD);
+
+	return (struct plt_entry){ cpu_to_le32(adrp), cpu_to_le32(add) };
+}
+
+struct plt_entry get_plt_entry(u64 dst, void *pc)
+{
+	struct plt_entry plt;
+	static u32 br;
+
+	if (!br)
+		br = aarch64_insn_gen_branch_reg(AARCH64_INSN_REG_16,
+						 AARCH64_INSN_BRANCH_NOLINK);
+
+	plt = __get_adrp_add_pair(dst, (u64)pc, AARCH64_INSN_REG_16);
+	plt.br = cpu_to_le32(br);
+
+	return plt;
+}
+
+bool plt_entries_equal(const struct plt_entry *a, const struct plt_entry *b)
+{
+	u64 p, q;
+
+	/*
+	 * Check whether both entries refer to the same target:
+	 * do the cheapest checks first.
+	 * If the 'add' or 'br' opcodes are different, then the target
+	 * cannot be the same.
+	 */
+	if (a->add != b->add || a->br != b->br)
+		return false;
+
+	p = ALIGN_DOWN((u64)a, SZ_4K);
+	q = ALIGN_DOWN((u64)b, SZ_4K);
+
+	/*
+	 * If the 'adrp' opcodes are the same then we just need to check
+	 * that they refer to the same 4k region.
+	 */
+	if (a->adrp == b->adrp && p == q)
+		return true;
+
+	return (p + aarch64_insn_adrp_get_offset(le32_to_cpu(a->adrp))) ==
+	       (q + aarch64_insn_adrp_get_offset(le32_to_cpu(b->adrp)));
+}
+
+static bool in_init(const struct module *mod, void *loc)
+{
+	return (u64)loc - (u64)mod->init_layout.base < mod->init_layout.size;
+}
+
+u64 module_emit_plt_entry(struct module *mod, Elf64_Shdr *sechdrs,
+			  void *loc, const Elf64_Rela *rela,
+			  Elf64_Sym *sym)
+{
+	struct mod_plt_sec *pltsec = !in_init(mod, loc) ? &mod->arch.core :
+							  &mod->arch.init;
+	struct plt_entry *plt = (struct plt_entry *)sechdrs[pltsec->plt_shndx].sh_addr;
+	int i = pltsec->plt_num_entries;
+	int j = i - 1;
+	u64 val = sym->st_value + rela->r_addend;
+
+	if (is_forbidden_offset_for_adrp(&plt[i].adrp))
+		i++;
+
+	plt[i] = get_plt_entry(val, &plt[i]);
+
+	/*
+	 * Check if the entry we just created is a duplicate. Given that the
+	 * relocations are sorted, this will be the last entry we allocated.
+	 * (if one exists).
+	 */
+	if (j >= 0 && plt_entries_equal(plt + i, plt + j))
+		return (u64)&plt[j];
+
+	pltsec->plt_num_entries += i - j;
+	if (WARN_ON(pltsec->plt_num_entries > pltsec->plt_max_entries))
+		return 0;
+
+	return (u64)&plt[i];
+}
+
+#ifdef CONFIG_ARM64_ERRATUM_843419
+u64 module_emit_veneer_for_adrp(struct module *mod, Elf64_Shdr *sechdrs,
+				void *loc, u64 val)
+{
+	struct mod_plt_sec *pltsec = !in_init(mod, loc) ? &mod->arch.core :
+							  &mod->arch.init;
+	struct plt_entry *plt = (struct plt_entry *)sechdrs[pltsec->plt_shndx].sh_addr;
+	int i = pltsec->plt_num_entries++;
+	u32 br;
+	int rd;
+
+	if (WARN_ON(pltsec->plt_num_entries > pltsec->plt_max_entries))
+		return 0;
+
+	if (is_forbidden_offset_for_adrp(&plt[i].adrp))
+		i = pltsec->plt_num_entries++;
+
+	/* get the destination register of the ADRP instruction */
+	rd = aarch64_insn_decode_register(AARCH64_INSN_REGTYPE_RD,
+					  le32_to_cpup((__le32 *)loc));
+
+	br = aarch64_insn_gen_branch_imm((u64)&plt[i].br, (u64)loc + 4,
+					 AARCH64_INSN_BRANCH_NOLINK);
+
+	plt[i] = __get_adrp_add_pair(val, (u64)&plt[i], rd);
+	plt[i].br = cpu_to_le32(br);
+
+	return (u64)&plt[i];
+}
+#endif
+
+#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,
+			       Elf64_Word dstidx, Elf_Shdr *dstsec)
+{
+	unsigned int ret = 0;
+	Elf64_Sym *s;
+	int i;
+
+	for (i = 0; i < num; i++) {
+		u64 min_align;
+
+		switch (ELF64_R_TYPE(rela[i].r_info)) {
+		case R_AARCH64_JUMP26:
+		case R_AARCH64_CALL26:
+			if (!IS_ENABLED(CONFIG_RANDOMIZE_BASE))
+				break;
+
+			/*
+			 * We only have to consider branch targets that resolve
+			 * to symbols that are defined in a different section.
+			 * This is not simply a heuristic, it is a fundamental
+			 * limitation, since there is no guaranteed way to emit
+			 * PLT entries sufficiently close to the branch if the
+			 * section size exceeds the range of a branch
+			 * instruction. So ignore relocations against defined
+			 * symbols if they live in the same section as the
+			 * relocation target.
+			 */
+			s = syms + ELF64_R_SYM(rela[i].r_info);
+			if (s->st_shndx == dstidx)
+				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;
+		case R_AARCH64_ADR_PREL_PG_HI21_NC:
+		case R_AARCH64_ADR_PREL_PG_HI21:
+			if (!IS_ENABLED(CONFIG_ARM64_ERRATUM_843419) ||
+			    !cpus_have_const_cap(ARM64_WORKAROUND_843419))
+				break;
+
+			/*
+			 * Determine the minimal safe alignment for this ADRP
+			 * instruction: the section alignment at which it is
+			 * guaranteed not to appear at a vulnerable offset.
+			 *
+			 * This comes down to finding the least significant zero
+			 * bit in bits [11:3] of the section offset, and
+			 * increasing the section's alignment so that the
+			 * resulting address of this instruction is guaranteed
+			 * to equal the offset in that particular bit (as well
+			 * as all less signficant bits). This ensures that the
+			 * address modulo 4 KB != 0xfff8 or 0xfffc (which would
+			 * have all ones in bits [11:3])
+			 */
+			min_align = 2ULL << ffz(rela[i].r_offset | 0x7);
+
+			/*
+			 * Allocate veneer space for each ADRP that may appear
+			 * at a vulnerable offset nonetheless. At relocation
+			 * time, some of these will remain unused since some
+			 * ADRP instructions can be patched to ADR instructions
+			 * instead.
+			 */
+			if (min_align > SZ_4K)
+				ret++;
+			else
+				dstsec->sh_addralign = max(dstsec->sh_addralign,
+							   min_align);
+			break;
+		}
+	}
+
+	if (IS_ENABLED(CONFIG_ARM64_ERRATUM_843419) &&
+	    cpus_have_const_cap(ARM64_WORKAROUND_843419))
+		/*
+		 * Add some slack so we can skip PLT slots that may trigger
+		 * the erratum due to the placement of the ADRP instruction.
+		 */
+		ret += DIV_ROUND_UP(ret, (SZ_4K / sizeof(struct plt_entry)));
+
+	return ret;
+}
+
+static bool branch_rela_needs_plt(Elf64_Sym *syms, Elf64_Rela *rela,
+				  Elf64_Word dstidx)
+{
+
+	Elf64_Sym *s = syms + ELF64_R_SYM(rela->r_info);
+
+	if (s->st_shndx == dstidx)
+		return false;
+
+	return ELF64_R_TYPE(rela->r_info) == R_AARCH64_JUMP26 ||
+	       ELF64_R_TYPE(rela->r_info) == R_AARCH64_CALL26;
+}
+
+/* Group branch PLT relas at the front end of the array. */
+static int partition_branch_plt_relas(Elf64_Sym *syms, Elf64_Rela *rela,
+				      int numrels, Elf64_Word dstidx)
+{
+	int i = 0, j = numrels - 1;
+
+	if (!IS_ENABLED(CONFIG_RANDOMIZE_BASE))
+		return 0;
+
+	while (i < j) {
+		if (branch_rela_needs_plt(syms, &rela[i], dstidx))
+			i++;
+		else if (branch_rela_needs_plt(syms, &rela[j], dstidx))
+			swap(rela[i], rela[j]);
+		else
+			j--;
+	}
+
+	return i;
+}
+
+int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
+			      char *secstrings, struct module *mod)
+{
+	unsigned long core_plts = 0;
+	unsigned long init_plts = 0;
+	Elf64_Sym *syms = NULL;
+	Elf_Shdr *pltsec, *tramp = 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(secstrings + sechdrs[i].sh_name, ".plt"))
+			mod->arch.core.plt_shndx = i;
+		else if (!strcmp(secstrings + sechdrs[i].sh_name, ".init.plt"))
+			mod->arch.init.plt_shndx = i;
+		else if (!strcmp(secstrings + sechdrs[i].sh_name,
+				 ".text.ftrace_trampoline"))
+			tramp = sechdrs + i;
+		else if (sechdrs[i].sh_type == SHT_SYMTAB)
+			syms = (Elf64_Sym *)sechdrs[i].sh_addr;
+	}
+
+	if (!mod->arch.core.plt_shndx || !mod->arch.init.plt_shndx) {
+		pr_err("%s: module PLT section(s) 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 nents, 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 branch relocations requiring a PLT by type, symbol index
+		 * and addend
+		 */
+		nents = partition_branch_plt_relas(syms, rels, numrels,
+						   sechdrs[i].sh_info);
+		if (nents)
+			sort(rels, nents, sizeof(Elf64_Rela), cmp_rela, NULL);
+
+		if (!module_init_layout_section(secstrings + dstsec->sh_name))
+			core_plts += count_plts(syms, rels, numrels,
+						sechdrs[i].sh_info, dstsec);
+		else
+			init_plts += count_plts(syms, rels, numrels,
+						sechdrs[i].sh_info, dstsec);
+	}
+
+	pltsec = sechdrs + mod->arch.core.plt_shndx;
+	pltsec->sh_type = SHT_NOBITS;
+	pltsec->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
+	pltsec->sh_addralign = L1_CACHE_BYTES;
+	pltsec->sh_size = (core_plts  + 1) * sizeof(struct plt_entry);
+	mod->arch.core.plt_num_entries = 0;
+	mod->arch.core.plt_max_entries = core_plts;
+
+	pltsec = sechdrs + mod->arch.init.plt_shndx;
+	pltsec->sh_type = SHT_NOBITS;
+	pltsec->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
+	pltsec->sh_addralign = L1_CACHE_BYTES;
+	pltsec->sh_size = (init_plts + 1) * sizeof(struct plt_entry);
+	mod->arch.init.plt_num_entries = 0;
+	mod->arch.init.plt_max_entries = init_plts;
+
+	if (tramp) {
+		tramp->sh_type = SHT_NOBITS;
+		tramp->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
+		tramp->sh_addralign = __alignof__(struct plt_entry);
+		tramp->sh_size = NR_FTRACE_PLTS * sizeof(struct plt_entry);
+	}
+
+	return 0;
+}