Commit a845c7cf authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Ingo Molnar
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objtool: Improve retpoline alternative handling



Currently objtool requires all retpolines to be:

  a) patched in with alternatives; and

  b) annotated with ANNOTATE_NOSPEC_ALTERNATIVE.

If you forget to do both of the above, objtool segfaults trying to
dereference a NULL 'insn->call_dest' pointer.

Avoid that situation and print a more helpful error message:

  quirks.o: warning: objtool: efi_delete_dummy_variable()+0x99: unsupported intra-function call
  quirks.o: warning: objtool: If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.

Future improvements can be made to make objtool smarter with respect to
retpolines, but this is a good incremental improvement for now.

Reported-and-tested-by: default avatarGuenter Roeck <linux@roeck-us.net>
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/819e50b6d9c2e1a22e34c1a636c0b2057cc8c6e5.1517284349.git.jpoimboe@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 7e86548e
......@@ -543,18 +543,14 @@ static int add_call_destinations(struct objtool_file *file)
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);
if (!insn->call_dest && !insn->ignore) {
WARN_FUNC("unsupported intra-function call",
insn->sec, insn->offset);
WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
return -1;
}
#endif
} else if (rela->sym->type == STT_SECTION) {
insn->call_dest = find_symbol_by_offset(rela->sym->sec,
rela->addend+4);
......@@ -648,6 +644,8 @@ static int handle_group_alt(struct objtool_file *file,
last_new_insn = insn;
insn->ignore = orig_insn->ignore_alts;
if (insn->type != INSN_JUMP_CONDITIONAL &&
insn->type != INSN_JUMP_UNCONDITIONAL)
continue;
......@@ -729,10 +727,6 @@ static int add_special_section_alts(struct objtool_file *file)
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,
......@@ -1089,11 +1083,11 @@ static int decode_sections(struct objtool_file *file)
if (ret)
return ret;
ret = add_call_destinations(file);
ret = add_special_section_alts(file);
if (ret)
return ret;
ret = add_special_section_alts(file);
ret = add_call_destinations(file);
if (ret)
return ret;
......@@ -1720,10 +1714,12 @@ static int validate_branch(struct objtool_file *file, struct instruction *first,
insn->visited = true;
list_for_each_entry(alt, &insn->alts, list) {
ret = validate_branch(file, alt->insn, state);
if (ret)
return 1;
if (!insn->ignore_alts) {
list_for_each_entry(alt, &insn->alts, list) {
ret = validate_branch(file, alt->insn, state);
if (ret)
return 1;
}
}
switch (insn->type) {
......
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