linux-kernel - [PATCH 3/3] [v2] objtool: add UACCESS exceptions for __tsan_volatile

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Message-Id: <20230215130058.3836177-4-arnd@kernel.org>
Date:   Wed, 15 Feb 2023 14:00:58 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kuan-Ying Lee <Kuan-Ying.Lee@...iatek.com>,
        Marco Elver <elver@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] [v2] objtool: add UACCESS exceptions for __tsan_volatile_read/write

From: Arnd Bergmann <arnd@...db.de>

A lot of the tsan helpers are already excempt from the UACCESS warnings,
but some more functions were added that need the same thing:

kernel/kcsan/core.o: warning: objtool: __tsan_volatile_read16+0x0: call to __tsan_unaligned_read16() with UACCESS enabled
kernel/kcsan/core.o: warning: objtool: __tsan_volatile_write16+0x0: call to __tsan_unaligned_write16() with UACCESS enabled
vmlinux.o: warning: objtool: __tsan_unaligned_volatile_read16+0x4: call to __tsan_unaligned_read16() with UACCESS enabled
vmlinux.o: warning: objtool: __tsan_unaligned_volatile_write16+0x4: call to __tsan_unaligned_write16() with UACCESS enabled

As Marco points out, these functions don't even call each other
explicitly but instead gcc (but not clang) notices the functions
being identical and turns one symbol into a direct branch to the
other.

Fixes: 75d75b7a4d54 ("kcsan: Support distinguishing volatile accesses")
Acked-by: Marco Elver <elver@...gle.com>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 tools/objtool/check.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index b0b467d9608a..da52ce861cc2 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1237,6 +1237,8 @@ static const char *uaccess_safe_builtin[] = {
 	"__tsan_atomic64_compare_exchange_val",
 	"__tsan_atomic_thread_fence",
 	"__tsan_atomic_signal_fence",
+	"__tsan_unaligned_read16",
+	"__tsan_unaligned_write16",
 	/* KCOV */
 	"write_comp_data",
 	"check_kcov_mode",
-- 
2.39.1