From: Peter Zijlstra peterz@infradead.org
commit 7a53f408902d913cd541b4f8ad7dbcd4961f5b82 upstream.
Since not all compilers have a function attribute to disable KCOV instrumentation, objtool can rewrite KCOV instrumentation in noinstr functions as per commit:
f56dae88a81f ("objtool: Handle __sanitize_cov*() tail calls")
However, this has subtle interaction with the SLS validation from commit:
1cc1e4c8aab4 ("objtool: Add straight-line-speculation validation")
In that when a tail-call instrucion is replaced with a RET an additional INT3 instruction is also written, but is not represented in the decoded instruction stream.
This then leads to false positive missing INT3 objtool warnings in noinstr code.
Instead of adding additional struct instruction objects, mark the RET instruction with retpoline_safe to suppress the warning (since we know there really is an INT3).
Fixes: 1cc1e4c8aab4 ("objtool: Add straight-line-speculation validation") Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lkml.kernel.org/r/20220323230712.GA8939@worktop.programming.kicks-as... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- tools/objtool/check.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
--- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -1090,6 +1090,17 @@ static void annotate_call_site(struct ob : arch_nop_insn(insn->len));
insn->type = sibling ? INSN_RETURN : INSN_NOP; + + if (sibling) { + /* + * We've replaced the tail-call JMP insn by two new + * insn: RET; INT3, except we only have a single struct + * insn here. Mark it retpoline_safe to avoid the SLS + * warning, instead of adding another insn. + */ + insn->retpoline_safe = true; + } + return; }