4.9-stable review patch. If anyone has any objections, please let me know.
------------------ From: Josh Poimboeuf <jpoim...@redhat.com> commit 258c76059cece01bebae098e81bacb1af2edad17 upstream. Getting objtool to understand retpolines is going to be a bit of a challenge. For now, take advantage of the fact that retpolines are patched in with alternatives. Just read the original (sane) non-alternative instruction, and ignore the patched-in retpoline. This allows objtool to understand the control flow *around* the retpoline, even if it can't yet follow what's inside. This means the ORC unwinder will fail to unwind from inside a retpoline, but will work fine otherwise. Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com> Signed-off-by: David Woodhouse <d...@amazon.co.uk> Signed-off-by: Thomas Gleixner <t...@linutronix.de> Cc: gno...@lxorguk.ukuu.org.uk Cc: Rik van Riel <r...@redhat.com> Cc: Andi Kleen <a...@linux.intel.com> Cc: thomas.lenda...@amd.com Cc: Peter Zijlstra <pet...@infradead.org> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Jiri Kosina <ji...@kernel.org> Cc: Andy Lutomirski <l...@amacapital.net> Cc: Dave Hansen <dave.han...@intel.com> Cc: Kees Cook <keesc...@google.com> Cc: Tim Chen <tim.c.c...@linux.intel.com> Cc: Greg Kroah-Hartman <gre...@linux-foundation.org> Cc: Paul Turner <p...@google.com> Link: https://lkml.kernel.org/r/1515707194-20531-3-git-send-email-d...@amazon.co.uk [dwmw2: Applies to tools/objtool/builtin-check.c not check.[ch]] Signed-off-by: David Woodhouse <d...@amazon.co.uk> Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org> --- tools/objtool/builtin-check.c | 64 +++++++++++++++++++++++++++++++++++++----- 1 file changed, 57 insertions(+), 7 deletions(-) --- a/tools/objtool/builtin-check.c +++ b/tools/objtool/builtin-check.c @@ -51,7 +51,7 @@ struct instruction { unsigned int len, state; unsigned char type; unsigned long immediate; - bool alt_group, visited; + bool alt_group, visited, ignore_alts; struct symbol *call_dest; struct instruction *jump_dest; struct list_head alts; @@ -353,6 +353,40 @@ static void add_ignores(struct objtool_f } /* + * FIXME: For now, just ignore any alternatives which add retpolines. This is + * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline. + * But it at least allows objtool to understand the control flow *around* the + * retpoline. + */ +static int add_nospec_ignores(struct objtool_file *file) +{ + struct section *sec; + struct rela *rela; + struct instruction *insn; + + sec = find_section_by_name(file->elf, ".rela.discard.nospec"); + if (!sec) + return 0; + + list_for_each_entry(rela, &sec->rela_list, list) { + if (rela->sym->type != STT_SECTION) { + WARN("unexpected relocation symbol type in %s", sec->name); + return -1; + } + + insn = find_insn(file, rela->sym->sec, rela->addend); + if (!insn) { + WARN("bad .discard.nospec entry"); + return -1; + } + + insn->ignore_alts = true; + } + + return 0; +} + +/* * Find the destination instructions for all jumps. */ static int add_jump_destinations(struct objtool_file *file) @@ -435,11 +469,18 @@ static int add_call_destinations(struct dest_off = insn->offset + insn->len + insn->immediate; insn->call_dest = find_symbol_by_offset(insn->sec, dest_off); + /* + * FIXME: Thanks to retpolines, it's now considered + * normal for a function to call within itself. So + * disable this warning for now. + */ +#if 0 if (!insn->call_dest) { WARN_FUNC("can't find call dest symbol at offset 0x%lx", insn->sec, insn->offset, dest_off); return -1; } +#endif } else if (rela->sym->type == STT_SECTION) { insn->call_dest = find_symbol_by_offset(rela->sym->sec, rela->addend+4); @@ -601,12 +642,6 @@ static int add_special_section_alts(stru return ret; list_for_each_entry_safe(special_alt, tmp, &special_alts, list) { - alt = malloc(sizeof(*alt)); - if (!alt) { - WARN("malloc failed"); - ret = -1; - goto out; - } orig_insn = find_insn(file, special_alt->orig_sec, special_alt->orig_off); @@ -617,6 +652,10 @@ static int add_special_section_alts(stru goto out; } + /* Ignore retpoline alternatives. */ + if (orig_insn->ignore_alts) + continue; + new_insn = NULL; if (!special_alt->group || special_alt->new_len) { new_insn = find_insn(file, special_alt->new_sec, @@ -642,6 +681,13 @@ static int add_special_section_alts(stru goto out; } + alt = malloc(sizeof(*alt)); + if (!alt) { + WARN("malloc failed"); + ret = -1; + goto out; + } + alt->insn = new_insn; list_add_tail(&alt->list, &orig_insn->alts); @@ -861,6 +907,10 @@ static int decode_sections(struct objtoo add_ignores(file); + ret = add_nospec_ignores(file); + if (ret) + return ret; + ret = add_jump_destinations(file); if (ret) return ret;
