[tip: x86/entry] x86/entry, ubsan, objtool: Whitelist __ubsan_handle_*()

[tip: x86/entry] x86/entry, ubsan, objtool: Whitelist __ubsan_handle_*()

[tip-bot2 for Peter Zijlstra]

The following commit has been merged into the x86/entry branch of tip:

Commit-ID:     6b643a07a7e41f9e11cfbb9bba4c5c9791ac2997
Gitweb:        https://git.kernel.org/tip/6b643a07a7e41f9e11cfbb9bba4c5c9791ac2997
Author:        Peter Zijlstra <peterz@infradead.org>
AuthorDate:    Wed, 03 Jun 2020 20:09:06 +02:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Mon, 15 Jun 2020 14:10:09 +02:00

x86/entry, ubsan, objtool: Whitelist __ubsan_handle_*()

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 <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Marco Elver <elver@google.com>
---
 include/linux/compiler_types.h |  2 +-
 tools/objtool/check.c          | 28 +++++++++++++++++++++++++++-
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 85b8d23..14513e8 100644
--- 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__ */
 
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 5fbb90a..3e214f8 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2190,10 +2190,36 @@ static inline const char *call_dest_name(struct instruction *insn)
 	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;