linux-kernel - [PATCH v2 23/23] objtool, kcsan: Remove memory barrier instrumentation from noinstr

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Date:   Thu, 18 Nov 2021 09:10:27 +0100
From:   Marco Elver <elver@...gle.com>
To:     elver@...gle.com, "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Alexander Potapenko <glider@...gle.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Waiman Long <longman@...hat.com>,
        Will Deacon <will@...nel.org>, kasan-dev@...glegroups.com,
        linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org
Subject: [PATCH v2 23/23] objtool, kcsan: Remove memory barrier
 instrumentation from noinstr

Teach objtool to turn instrumentation required for memory barrier
modeling into nops in noinstr text.

The __tsan_func_entry/exit calls are still emitted by compilers even
with the __no_sanitize_thread attribute. The memory barrier
instrumentation will be inserted explicitly (without compiler help), and
thus needs to also explicitly be removed.

Signed-off-by: Marco Elver <elver@...gle.com>
---
v2:
* Rewrite after rebase to v5.16-rc1.
---
 tools/objtool/check.c               | 37 ++++++++++++++++++++++-------
 tools/objtool/include/objtool/elf.h |  2 +-
 2 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 61dfb66b30b6..2b2587e5ec69 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1071,12 +1071,7 @@ static void annotate_call_site(struct objtool_file *file,
 		return;
 	}
 
-	/*
-	 * Many compilers cannot disable KCOV with a function attribute
-	 * so they need a little help, NOP out any KCOV calls from noinstr
-	 * text.
-	 */
-	if (insn->sec->noinstr && sym->kcov) {
+	if (insn->sec->noinstr && sym->removable_instr) {
 		if (reloc) {
 			reloc->type = R_NONE;
 			elf_write_reloc(file->elf, reloc);
@@ -1991,6 +1986,32 @@ static int read_intra_function_calls(struct objtool_file *file)
 	return 0;
 }
 
+static bool is_removable_instr(const char *name)
+{
+	/*
+	 * Many compilers cannot disable KCOV with a function attribute so they
+	 * need a little help, NOP out any KCOV calls from noinstr text.
+	 */
+	if (!strncmp(name, "__sanitizer_cov_", 16))
+		return true;
+
+	/*
+	 * Compilers currently do not remove __tsan_func_entry/exit with the
+	 * __no_sanitize_thread attribute, remove them.
+	 *
+	 * Memory barrier instrumentation is not emitted by the compiler, but
+	 * inserted explicitly, so we need to also remove them.
+	 */
+	if (!strncmp(name, "__tsan_func_", 12) ||
+	    !strcmp(name, "__kcsan_mb") ||
+	    !strcmp(name, "__kcsan_wmb") ||
+	    !strcmp(name, "__kcsan_rmb") ||
+	    !strcmp(name, "__kcsan_release"))
+		return true;
+
+	return false;
+}
+
 static int classify_symbols(struct objtool_file *file)
 {
 	struct section *sec;
@@ -2011,8 +2032,8 @@ static int classify_symbols(struct objtool_file *file)
 			if (!strcmp(func->name, "__fentry__"))
 				func->fentry = true;
 
-			if (!strncmp(func->name, "__sanitizer_cov_", 16))
-				func->kcov = true;
+			if (is_removable_instr(func->name))
+				func->removable_instr = true;
 		}
 	}
 
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index cdc739fa9a6f..62e790a09ad2 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -58,7 +58,7 @@ struct symbol {
 	u8 static_call_tramp : 1;
 	u8 retpoline_thunk   : 1;
 	u8 fentry            : 1;
-	u8 kcov              : 1;
+	u8 removable_instr   : 1;
 	struct list_head pv_target;
 };
 
-- 
2.34.0.rc2.393.gf8c9666880-goog