Commit 0c314a88 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Ingo Molnar
Browse files

objtool: Fix stack overflow in validate_branch() 



On an allmodconfig kernel compiled with Clang, objtool is segfaulting in
drivers/scsi/qla2xxx/qla2xxx.o due to a stack overflow in
validate_branch().

Due in part to KASAN being enabled, the qla2xxx code has a large number
of conditional jumps, causing objtool to go quite deep in its recursion.

By far the biggest offender of stack usage is the recently added
'prev_state' stack variable in validate_insn(), coming in at 328 bytes.

Move that variable (and its tracing usage) to handle_insn_ops() and make
handle_insn_ops() noinline to keep its stack frame outside the recursive
call chain.

Reported-by: default avatarNathan Chancellor <nathan@kernel.org>
Fixes: fcb268b4 ("objtool: Trace instruction state changes during function validation")
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/21bb161c23ca0d8c942a960505c0d327ca2dc7dc.1764691895.git.jpoimboe@kernel.org
Closes: https://lore.kernel.org/20251201202329.GA3225984@ax162
parent 4a26e703

tools/objtool/check.c

+13 −14
Original line number Diff line number Diff line
@@ -3282,18 +3282,19 @@ static int propagate_alt_cfi(struct objtool_file *file, struct instruction *insn 
	return 0;

}



static int handle_insn_ops(struct instruction *insn,

static int noinline handle_insn_ops(struct instruction *insn,

				    struct instruction *next_insn,

				    struct insn_state *state)

{

	struct insn_state prev_state __maybe_unused = *state;

	struct stack_op *op;

	int ret;

	int ret = 0;



	for (op = insn->stack_ops; op; op = op->next) {



		ret = update_cfi_state(insn, next_insn, &state->cfi, op);

		if (ret)

			return ret;

			goto done;



		if (!opts.uaccess || !insn->alt_group)

			continue;
@@ -3303,7 +3304,8 @@ static int handle_insn_ops(struct instruction *insn, 
				state->uaccess_stack = 1;

			} else if (state->uaccess_stack >> 31) {

				WARN_INSN(insn, "PUSHF stack exhausted");

				return 1;

				ret = 1;

				goto done;

			}

			state->uaccess_stack <<= 1;

			state->uaccess_stack  |= state->uaccess;
@@ -3319,7 +3321,10 @@ static int handle_insn_ops(struct instruction *insn, 
		}

	}



	return 0;

done:

	TRACE_INSN_STATE(insn, &prev_state, state);



	return ret;

}



static bool insn_cfi_match(struct instruction *insn, struct cfi_state *cfi2)
@@ -3694,8 +3699,6 @@ static int validate_insn(struct objtool_file *file, struct symbol *func, 
			 struct instruction *prev_insn, struct instruction *next_insn,

			 bool *dead_end)

{

	/* prev_state and alt_name are not used if there is no disassembly support */

	struct insn_state prev_state __maybe_unused;

	char *alt_name __maybe_unused = NULL;

	struct alternative *alt;

	u8 visited;
@@ -3798,11 +3801,7 @@ static int validate_insn(struct objtool_file *file, struct symbol *func, 
	if (skip_alt_group(insn))

		return 0;



	prev_state = *statep;

	ret = handle_insn_ops(insn, next_insn, statep);

	TRACE_INSN_STATE(insn, &prev_state, statep);



	if (ret)

	if (handle_insn_ops(insn, next_insn, statep))

		return 1;



	switch (insn->type) {