The following commit has been merged into the objtool/core branch of tip:
Commit-ID: 8c0cca513be9e3dd9c17b55b72b66751f3487577
Gitweb:
https://git.kernel.org/tip/8c0cca513be9e3dd9c17b55b72b66751f3487577
Author: Peter Zijlstra <pet...@infradead.org>
AuthorDate: Thu, 11 Feb 2021 13:03:28 +01:00
Committer: Peter Zijlstra <pet...@infradead.org>
CommitterDate: Wed, 03 Mar 2021 09:38:29 +01:00
objtool: Allow UNWIND_HINT to suppress dodgy stack modifications
rewind_stack_do_exit()
UNWIND_HINT_FUNC
/* Prevent any naive code from trying to unwind to our caller. */
xorl %ebp, %ebp
movq PER_CPU_VAR(cpu_current_top_of_stack), %rax
leaq -PTREGS_SIZE(%rax), %rsp
UNWIND_HINT_REGS
call do_exit
Does unspeakable things to the stack, which objtool currently fails to
detect due to a limitation in instruction decoding. This will be
rectified after which the above will result in:
arch/x86/entry/entry_64.o: warning: objtool: .text+0xab: unsupported stack
register modification
Allow the UNWIND_HINT on the next instruction to suppress this, it
will overwrite the state anyway.
Suggested-by: Josh Poimboeuf <jpoim...@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Acked-by: Josh Poimboeuf <jpoim...@redhat.com>
Tested-by: Nick Desaulniers <ndesaulni...@google.com>
Link: https://lkml.kernel.org/r/20210211173626.918498...@infradead.org
---
tools/objtool/check.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 068cdb4..12b8f0f 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1959,8 +1959,9 @@ static void restore_reg(struct cfi_state *cfi, unsigned
char reg)
* 41 5d pop %r13
* c3 retq
*/
-static int update_cfi_state(struct instruction *insn, struct cfi_state *cfi,
- struct stack_op *op)
+static int update_cfi_state(struct instruction *insn,
+ struct instruction *next_insn,
+ struct cfi_state *cfi, struct stack_op *op)
{
struct cfi_reg *cfa = &cfi->cfa;
struct cfi_reg *regs = cfi->regs;
@@ -2161,7 +2162,7 @@ static int update_cfi_state(struct instruction *insn,
struct cfi_state *cfi,
break;
}
- if (op->dest.reg == cfi->cfa.base) {
+ if (op->dest.reg == cfi->cfa.base && !(next_insn &&
next_insn->hint)) {
WARN_FUNC("unsupported stack register
modification",
insn->sec, insn->offset);
return -1;
@@ -2433,13 +2434,15 @@ static int propagate_alt_cfi(struct objtool_file *file,
struct instruction *insn
return 0;
}
-static int handle_insn_ops(struct instruction *insn, struct insn_state *state)
+static int handle_insn_ops(struct instruction *insn,
+ struct instruction *next_insn,
+ struct insn_state *state)
{
struct stack_op *op;
list_for_each_entry(op, &insn->stack_ops, list) {
- if (update_cfi_state(insn, &state->cfi, op))
+ if (update_cfi_state(insn, next_insn, &state->cfi, op))
return 1;
if (op->dest.type == OP_DEST_PUSHF) {
@@ -2719,7 +2722,7 @@ static int validate_branch(struct objtool_file *file,
struct symbol *func,
return 0;
}
- if (handle_insn_ops(insn, &state))
+ if (handle_insn_ops(insn, next_insn, &state))
return 1;
switch (insn->type) {
