On Wed, Jun 03, 2020 at 06:07:22PM +0200, Peter Zijlstra wrote:
> On Wed, Jun 03, 2020 at 04:47:54PM +0200, Marco Elver wrote:
> > With that in mind, you could whitelist "__ubsan_handle"-prefixed
> > functions in objtool. Given the __always_inline+noinstr+__ubsan_handle
> > case is quite rare, it might be reasonable.
>
> Yes, I think so. Let me go have dinner and then I'll try and do a patch
> to that effect.
Here's a slightly more radical patch, it unconditionally allows UBSAN.
I've not actually boot tested this.. yet.
---
Subject: x86/entry, ubsan, objtool: Whitelist __ubsan_handle_*()
From: Peter Zijlstra <pet...@infradead.org>
Date: Wed Jun 3 20:09:06 CEST 2020
The UBSAN instrumentation only inserts external CALLs when things go
'BAD', much like WARN(). So treat them similar to WARN()s for noinstr,
that is: allow them, at the risk of taking the machine down, to get
their message out.
Suggested-by: Marco Elver <el...@google.com>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
include/linux/compiler_types.h | 2 +-
tools/objtool/check.c | 28 +++++++++++++++++++++++++++-
2 files changed, 28 insertions(+), 2 deletions(-)
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -199,7 +199,7 @@ struct ftrace_likely_data {
/* Section for code which can't be instrumented at all */
#define noinstr
\
noinline notrace __attribute((__section__(".noinstr.text"))) \
- __no_kcsan __no_sanitize_address __no_sanitize_undefined
+ __no_kcsan __no_sanitize_address
#endif /* __KERNEL__ */
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2190,10 +2190,36 @@ static inline const char *call_dest_name
return "{dynamic}";
}
+static inline bool noinstr_call_dest(struct symbol *func)
+{
+ /*
+ * We can't deal with indirect function calls at present;
+ * assume they're instrumented.
+ */
+ if (!func)
+ return false;
+
+ /*
+ * If the symbol is from a noinstr section; we good.
+ */
+ if (func->sec->noinstr)
+ return true;
+
+ /*
+ * The __ubsan_handle_*() calls are like WARN(), they only happen when
+ * something 'BAD' happened. At the risk of taking the machine down,
+ * let them proceed to get the message out.
+ */
+ if (!strncmp(func->name, "__ubsan_handle_", 15))
+ return true;
+
+ return false;
+}
+
static int validate_call(struct instruction *insn, struct insn_state *state)
{
if (state->noinstr && state->instr <= 0 &&
- (!insn->call_dest || !insn->call_dest->sec->noinstr)) {
+ !noinstr_call_dest(insn->call_dest)) {
WARN_FUNC("call to %s() leaves .noinstr.text section",
insn->sec, insn->offset, call_dest_name(insn));
return 1;
