From 90b7a5df152a64d2bea20beb438e8b81049a5c30 Mon Sep 17 00:00:00 2001 From: Fangrui Song Date: Wed, 22 Jun 2022 10:55:12 -0700 Subject: [PATCH] aarch64: Disallow copy relocations on protected data If an executable has copy relocations for extern protected data, that can only work if the shared object containing the definition is built with assumptions (a) the compiler emits GOT-generating relocations (b) the linker produces R_*_GLOB_DAT instead of R_*_RELATIVE. Otherwise the shared object uses its own definition directly and the executable accesses a stale copy. Note: the GOT relocations defeat the purpose of protected visibility as an optimization, and it turns out this never worked perfectly. glibc 2.36 will warn on copy relocations on protected data. Let's produce a warning at link time, matching ld.lld which has been used on many aarch64 OSes. Note: x86 requires GNU_PROPERTY_NO_COPY_ON_PROTECTED to have the error. This is to largely due to GCC 5's "x86-64: Optimize access to globals in PIE with copy reloc" which started to use direct access relocations for external data symbols in -fpie mode. GCC's aarch64 port does not have the change. Nowadays with most builds switching to -fpie/-fpic, aarch64 mostly doesn't need to worry about copy relocations. So for aarch64 we simply don't check GNU_PROPERTY_NO_COPY_ON_PROTECTED. --- bfd/elfnn-aarch64.c | 28 ++++++++++++++++++- ld/testsuite/ld-aarch64/aarch64-elf.exp | 9 ++++++ .../ld-aarch64/copy-reloc-protected.d | 2 ++ ld/testsuite/ld-aarch64/protected.s | 8 ++++++ 4 files changed, 46 insertions(+), 1 deletion(-) create mode 100644 ld/testsuite/ld-aarch64/copy-reloc-protected.d create mode 100644 ld/testsuite/ld-aarch64/protected.s diff --git a/bfd/elfnn-aarch64.c b/bfd/elfnn-aarch64.c index ca24a6b5678..81311fc5a32 100644 --- a/bfd/elfnn-aarch64.c +++ b/bfd/elfnn-aarch64.c @@ -2579,6 +2579,9 @@ struct elf_aarch64_link_hash_entry this symbol. */ unsigned int got_type; + /* TRUE if symbol is defined as a protected symbol. */ + unsigned int def_protected : 1; + /* A pointer to the most recently used stub hash entry against this symbol. */ struct elf_aarch64_stub_hash_entry *stub_cache; @@ -2855,9 +2858,16 @@ elfNN_aarch64_copy_indirect_symbol (struct bfd_link_info *info, static void elfNN_aarch64_merge_symbol_attribute (struct elf_link_hash_entry *h, unsigned int st_other, - bool definition ATTRIBUTE_UNUSED, + bool definition, bool dynamic ATTRIBUTE_UNUSED) { + if (definition) + { + struct elf_aarch64_link_hash_entry *eh + = (struct elf_aarch64_link_hash_entry *)h; + eh->def_protected = ELF_ST_VISIBILITY (st_other) == STV_PROTECTED; + } + unsigned int isym_sto = st_other & ~ELF_ST_VISIBILITY (-1); unsigned int h_sto = h->other & ~ELF_ST_VISIBILITY (-1); @@ -8701,6 +8711,22 @@ elfNN_aarch64_allocate_dynrelocs (struct elf_link_hash_entry *h, void *inf) if (h->dyn_relocs == NULL) return true; + for (p = h->dyn_relocs; p != NULL; p = p->next) + if (eh->def_protected) + { + /* Disallow copy relocations against protected symbol. */ + asection *s = p->sec->output_section; + if (s != NULL && (s->flags & SEC_READONLY) != 0) + { + info->callbacks->einfo + /* xgettext:c-format */ + (_ ("%F%P: %pB: copy relocation against non-copyable " + "protected symbol `%s'\n"), + p->sec->owner, h->root.root.string); + return false; + } + } + /* In the shared -Bsymbolic case, discard space allocated for dynamic pc-relative relocs against symbols which turn out to be defined in regular objects. For the normal shared case, discard diff --git a/ld/testsuite/ld-aarch64/aarch64-elf.exp b/ld/testsuite/ld-aarch64/aarch64-elf.exp index 64476f111e0..31162277bd9 100644 --- a/ld/testsuite/ld-aarch64/aarch64-elf.exp +++ b/ld/testsuite/ld-aarch64/aarch64-elf.exp @@ -407,6 +407,8 @@ set aarch64elflinktests { {copy-reloc-exe-2.s} {{objdump -R copy-reloc-2.d}} "copy-reloc-2"} {"ld-aarch64/exe with copy relocation elimination" "-e0 tmpdir/copy-reloc-so.so" "" "" {copy-reloc-exe-eliminate.s} {{objdump -R copy-reloc-eliminate.d}} "copy-reloc-elimination"} + {"Build .so with protected data" "-shared" "" "" {protected.s} + {} "protected.so"} {"ld-aarch64/so with global func" "-shared" "" "" {func-in-so.s} {} "func-in-so.so"} {"ld-aarch64/func sym hash opt for exe" @@ -416,8 +418,15 @@ set aarch64elflinktests { {} "libbti-plt-so.so"} } +set aarch64elfcclinktests [list \ + [list "copy relocation on protected data" \ + "-no-pie tmpdir/copy-reloc-exe.o tmpdir/protected.so" "" \ + {} {{error_output copy-reloc-protected.d}} "copy-reloc-protected"] +] + if [check_shared_lib_support] { run_ld_link_tests $aarch64elflinktests + run_cc_link_tests $aarch64elfcclinktests } run_dump_test "bti-plt-3" diff --git a/ld/testsuite/ld-aarch64/copy-reloc-protected.d b/ld/testsuite/ld-aarch64/copy-reloc-protected.d new file mode 100644 index 00000000000..99a356a3df6 --- /dev/null +++ b/ld/testsuite/ld-aarch64/copy-reloc-protected.d @@ -0,0 +1,2 @@ +.*: tmpdir/copy-reloc-exe.o: copy relocation against non-copyable protected symbol `global_a' +#... diff --git a/ld/testsuite/ld-aarch64/protected.s b/ld/testsuite/ld-aarch64/protected.s new file mode 100644 index 00000000000..eb3fb402dc4 --- /dev/null +++ b/ld/testsuite/ld-aarch64/protected.s @@ -0,0 +1,8 @@ +.global global_a +.protected global_a +.type global_a, %object +.size global_a, 4 + +.data +global_a: +.word 0xcafedead -- 2.30.2