From: Alexandre Chartre <[email protected]> Currently objtool prevents any branch to an alternative. While preventing branching from the outside to the middle of an alternative makes perfect sense, branching within the same alternative should be allowed. To do so, identify each alternative and check that a branch to an alternative comes from the same alternative.
Signed-off-by: Alexandre Chartre <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Link: https://lkml.kernel.org/r/[email protected] --- tools/objtool/check.c | 26 ++++++++++++++++++++------ tools/objtool/check.h | 3 ++- 2 files changed, 22 insertions(+), 7 deletions(-) --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -770,7 +770,9 @@ static int handle_group_alt(struct objto struct instruction *orig_insn, struct instruction **new_insn) { + static unsigned int alt_group_next_index = 1; struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL; + unsigned int alt_group = alt_group_next_index++; unsigned long dest_off; last_orig_insn = NULL; @@ -779,7 +781,7 @@ static int handle_group_alt(struct objto if (insn->offset >= special_alt->orig_off + special_alt->orig_len) break; - insn->alt_group = true; + insn->alt_group = alt_group; last_orig_insn = insn; } @@ -813,6 +815,7 @@ static int handle_group_alt(struct objto } last_new_insn = NULL; + alt_group = alt_group_next_index++; insn = *new_insn; sec_for_each_insn_from(file, insn) { if (insn->offset >= special_alt->new_off + special_alt->new_len) @@ -822,6 +825,7 @@ static int handle_group_alt(struct objto insn->ignore = orig_insn->ignore_alts; insn->func = orig_insn->func; + insn->alt_group = alt_group; /* * Since alternative replacement code is copy/pasted by the @@ -2163,6 +2167,15 @@ static int validate_return(struct symbol return 0; } +static bool is_branch_to_alternative(struct instruction *from, + struct instruction *to) +{ + if (!from || !to->alt_group || !list_empty(&to->alts)) + return false; + + return (from->alt_group != to->alt_group); +} + /* * Follow the branch starting at the given instruction, and recursively follow * any other branches (jumps). Meanwhile, track the frame pointer state at @@ -2170,6 +2183,7 @@ static int validate_return(struct symbol * tools/objtool/Documentation/stack-validation.txt. */ static int validate_branch(struct objtool_file *file, struct symbol *func, + struct instruction *from, struct instruction *insn, struct insn_state state) { struct alternative *alt; @@ -2180,7 +2194,7 @@ static int validate_branch(struct objtoo sec = insn->sec; - if (insn->alt_group && list_empty(&insn->alts)) { + if (is_branch_to_alternative(from, insn)) { WARN_FUNC("don't know how to handle branch to middle of alternative instruction group", sec, insn->offset); return 1; @@ -2227,7 +2241,7 @@ static int validate_branch(struct objtoo if (alt->skip_orig) skip_orig = true; - ret = validate_branch(file, func, alt->insn, state); + ret = validate_branch(file, func, NULL, alt->insn, state); if (ret) { if (backtrace) BT_FUNC("(alt)", insn); @@ -2271,7 +2285,7 @@ static int validate_branch(struct objtoo } else if (insn->jump_dest) { ret = validate_branch(file, func, - insn->jump_dest, state); + insn, insn->jump_dest, state); if (ret) { if (backtrace) BT_FUNC("(branch)", insn); @@ -2402,7 +2416,7 @@ static int validate_unwind_hints(struct while (&insn->list != &file->insn_list && (!sec || insn->sec == sec)) { if (insn->hint && !insn->visited) { - ret = validate_branch(file, insn->func, insn, state); + ret = validate_branch(file, insn->func, NULL, insn, state); if (ret && backtrace) BT_FUNC("<=== (hint)", insn); warnings += ret; @@ -2543,7 +2557,7 @@ static int validate_symbol(struct objtoo state->uaccess = sym->uaccess_safe; - ret = validate_branch(file, insn->func, insn, *state); + ret = validate_branch(file, insn->func, NULL, insn, *state); if (ret && backtrace) BT_FUNC("<=== (sym)", insn); return ret; --- a/tools/objtool/check.h +++ b/tools/objtool/check.h @@ -30,12 +30,13 @@ struct instruction { unsigned int len; enum insn_type type; unsigned long immediate; - bool alt_group, dead_end, ignore, ignore_alts; + bool dead_end, ignore, ignore_alts; bool hint; bool retpoline_safe; s8 instr; u8 visited; u8 ret_offset; + int alt_group; struct symbol *call_dest; struct instruction *jump_dest; struct instruction *first_jump_src;
