[PATCH 0/3] [v2] objtool warning fixes

[PATCH 0/3] [v2] objtool warning fixes

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

These are three of the easier fixes for objtool warnings around
kasan/kmsan/kcsan. I dropped one patch since Peter had come up
with a better fix, and adjusted the changelog text based on
feedback.

Link: https://lore.kernel.org/all/20230208164011.2287122-1-arnd@kernel.org/

Arnd Bergmann (3):
  [v2] kasan: mark addr_has_metadata __always_inline
  [v2] kmsan: disable ftrace in kmsan core code
  [v2] objtool: add UACCESS exceptions for __tsan_volatile_read/write

 mm/kasan/kasan.h      | 4 ++--
 mm/kmsan/Makefile     | 8 +++++++-
 tools/objtool/check.c | 2 ++
 3 files changed, 11 insertions(+), 3 deletions(-)

Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Kuan-Ying Lee <Kuan-Ying.Lee@mediatek.com>
Cc: Marco Elver <elver@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: kasan-dev@googlegroups.com
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org

-- 
2.39.1

[PATCH 1/3] [v2] kasan: mark addr_has_metadata __always_inline

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

When the compiler decides not to inline this function, objtool
complains about incorrect UACCESS state:

mm/kasan/generic.o: warning: objtool: __asan_load2+0x11: call to addr_has_metadata() with UACCESS enabled

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Marco Elver <elver@google.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
v2: fix objdump/objtool typo
---
 mm/kasan/kasan.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 3231314e071f..9377b0789edc 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -297,7 +297,7 @@ static inline const void *kasan_shadow_to_mem(const void *shadow_addr)
 		<< KASAN_SHADOW_SCALE_SHIFT);
 }
 
-static inline bool addr_has_metadata(const void *addr)
+static __always_inline bool addr_has_metadata(const void *addr)
 {
 	return (kasan_reset_tag(addr) >=
 		kasan_shadow_to_mem((void *)KASAN_SHADOW_START));
@@ -316,7 +316,7 @@ bool kasan_check_range(unsigned long addr, size_t size, bool write,
 
 #else /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
 
-static inline bool addr_has_metadata(const void *addr)
+static __always_inline bool addr_has_metadata(const void *addr)
 {
 	return (is_vmalloc_addr(addr) || virt_addr_valid(addr));
 }
-- 
2.39.1

[PATCH 2/3] [v2] kmsan: disable ftrace in kmsan core code

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

objtool warns about some suspicous code inside of kmsan:

vmlinux.o: warning: objtool: __msan_metadata_ptr_for_load_n+0x4: call to __fentry__() with UACCESS enabled
vmlinux.o: warning: objtool: __msan_metadata_ptr_for_store_n+0x4: call to __fentry__() with UACCESS enabled
vmlinux.o: warning: objtool: __msan_metadata_ptr_for_load_1+0x4: call to __fentry__() with UACCESS enabled
vmlinux.o: warning: objtool: __msan_metadata_ptr_for_store_1+0x4: call to __fentry__() with UACCESS enabled
vmlinux.o: warning: objtool: __msan_metadata_ptr_for_load_2+0x4: call to __fentry__() with UACCESS enabled
vmlinux.o: warning: objtool: __msan_metadata_ptr_for_store_2+0x4: call to __fentry__() with UACCESS enabled
vmlinux.o: warning: objtool: __msan_metadata_ptr_for_load_4+0x4: call to __fentry__() with UACCESS enabled
vmlinux.o: warning: objtool: __msan_metadata_ptr_for_store_4+0x4: call to __fentry__() with UACCESS enabled
vmlinux.o: warning: objtool: __msan_metadata_ptr_for_load_8+0x4: call to __fentry__() with UACCESS enabled
vmlinux.o: warning: objtool: __msan_metadata_ptr_for_store_8+0x4: call to __fentry__() with UACCESS enabled
vmlinux.o: warning: objtool: __msan_instrument_asm_store+0x4: call to __fentry__() with UACCESS enabled
vmlinux.o: warning: objtool: __msan_chain_origin+0x4: call to __fentry__() with UACCESS enabled
vmlinux.o: warning: objtool: __msan_poison_alloca+0x4: call to __fentry__() with UACCESS enabled
vmlinux.o: warning: objtool: __msan_warning+0x4: call to __fentry__() with UACCESS enabled
vmlinux.o: warning: objtool: __msan_get_context_state+0x4: call to __fentry__() with UACCESS enabled
vmlinux.o: warning: objtool: kmsan_copy_to_user+0x4: call to __fentry__() with UACCESS enabled
vmlinux.o: warning: objtool: kmsan_unpoison_memory+0x4: call to __fentry__() with UACCESS enabled
vmlinux.o: warning: objtool: kmsan_unpoison_entry_regs+0x4: call to __fentry__() with UACCESS enabled
vmlinux.o: warning: objtool: kmsan_report+0x4: call to __fentry__() with UACCESS enabled

The Makefile contained a line to turn off ftrace for the entire directory,
but this does not work. Replace it with individual lines, matching the
approach in kasan.

Fixes: f80be4571b19 ("kmsan: add KMSAN runtime core")
Acked-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
v2: remove the old "CFLAGS_REMOVE.o = $(CC_FLAGS_FTRACE)" line
---
 mm/kmsan/Makefile | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/mm/kmsan/Makefile b/mm/kmsan/Makefile
index 98eab2856626..91cfdde642d1 100644
--- a/mm/kmsan/Makefile
+++ b/mm/kmsan/Makefile
@@ -14,7 +14,13 @@ CC_FLAGS_KMSAN_RUNTIME := -fno-stack-protector
 CC_FLAGS_KMSAN_RUNTIME += $(call cc-option,-fno-conserve-stack)
 CC_FLAGS_KMSAN_RUNTIME += -DDISABLE_BRANCH_PROFILING
 
-CFLAGS_REMOVE.o = $(CC_FLAGS_FTRACE)
+# Disable ftrace to avoid recursion.
+CFLAGS_REMOVE_core.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_hooks.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_init.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_instrumentation.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_report.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_shadow.o = $(CC_FLAGS_FTRACE)
 
 CFLAGS_core.o := $(CC_FLAGS_KMSAN_RUNTIME)
 CFLAGS_hooks.o := $(CC_FLAGS_KMSAN_RUNTIME)
-- 
2.39.1

[PATCH 3/3] [v2] objtool: add UACCESS exceptions for __tsan_volatile_read/write

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.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@google.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.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