[PATCH 0/3] KCSAN cleanups and noinstr

[PATCH 0/3] KCSAN cleanups and noinstr

[Peter Zijlstra]

Hi all,

Here's two KCSAN cleanups and the required noinstr change for x86.

[PATCH 1/3] x86, kcsan: Remove __no_kcsan_or_inline usage

[Peter Zijlstra]

Now that KCSAN relies on -tsan-distinguish-volatile we no longer need
the annotation for constant_test_bit(). Remove it.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/include/asm/bitops.h |    6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

--- a/arch/x86/include/asm/bitops.h
+++ b/arch/x86/include/asm/bitops.h
@@ -201,12 +201,8 @@ arch_test_and_change_bit(long nr, volati
 	return GEN_BINARY_RMWcc(LOCK_PREFIX __ASM_SIZE(btc), *addr, c, "Ir", nr);
 }
 
-static __no_kcsan_or_inline bool constant_test_bit(long nr, const volatile unsigned long *addr)
+static __always_inline bool constant_test_bit(long nr, const volatile unsigned long *addr)
 {
-	/*
-	 * Because this is a plain access, we need to disable KCSAN here to
-	 * avoid double instrumentation via instrumented bitops.
-	 */
 	return ((1UL << (nr & (BITS_PER_LONG-1))) &
 		(addr[nr >> _BITOPS_LONG_SHIFT])) != 0;
 }

[PATCH 2/3] kcsan: Remove __no_kcsan_or_inline

[Peter Zijlstra]

There are no more user of this function attribute, also, with us now
actively supporting '__no_kcsan inline' it doesn't make sense to have
in any case.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 Documentation/dev-tools/kcsan.rst |    6 ------
 include/linux/compiler_types.h    |    5 +----
 2 files changed, 1 insertion(+), 10 deletions(-)

--- a/Documentation/dev-tools/kcsan.rst
+++ b/Documentation/dev-tools/kcsan.rst
@@ -114,12 +114,6 @@ functions, compilation units, or entire
   To dynamically limit for which functions to generate reports, see the
   `DebugFS interface`_ blacklist/whitelist feature.
 
-  For ``__always_inline`` functions, replace ``__always_inline`` with
-  ``__no_kcsan_or_inline`` (which implies ``__always_inline``)::
-
-    static __no_kcsan_or_inline void foo(void) {
-        ...
-
 * To disable data race detection for a particular compilation unit, add to the
   ``Makefile``::
 
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -193,10 +193,7 @@ struct ftrace_likely_data {
 
 #define __no_kcsan __no_sanitize_thread
 #ifdef __SANITIZE_THREAD__
-# define __no_kcsan_or_inline __no_kcsan notrace __maybe_unused
-# define __no_sanitize_or_inline __no_kcsan_or_inline
-#else
-# define __no_kcsan_or_inline __always_inline
+# define __no_sanitize_or_inline __no_kcsan notrace __maybe_unused
 #endif
 
 #ifndef __no_sanitize_or_inline

[PATCH 3/3] x86, kcsan: Add __no_kcsan to noinstr

[Peter Zijlstra]

The 'noinstr' function attribute means no-instrumentation, this should
very much include *SAN. Because lots of that is broken at present,
only include KCSAN for now, as that is limited to clang11, which has
sane function attribute behaviour.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 include/linux/compiler_types.h |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -118,10 +118,6 @@ struct ftrace_likely_data {
 #define notrace			__attribute__((__no_instrument_function__))
 #endif
 
-/* Section for code which can't be instrumented at all */
-#define noinstr								\
-	noinline notrace __attribute((__section__(".noinstr.text")))
-
 /*
  * it doesn't make sense on ARM (currently the only user of __naked)
  * to trace naked functions because then mcount is called without
@@ -200,6 +196,10 @@ struct ftrace_likely_data {
 #define __no_sanitize_or_inline __always_inline
 #endif
 
+/* Section for code which can't be instrumented at all */
+#define noinstr								\
+	noinline notrace __attribute((__section__(".noinstr.text"))) __no_kcsan
+
 #endif /* __KERNEL__ */
 
 #endif /* __ASSEMBLY__ */

Re: [PATCH 0/3] KCSAN cleanups and noinstr

[Marco Elver]

On Tue, 2 Jun 2020 at 19:34, Peter Zijlstra <peterz@infradead.org> wrote:
>
> Hi all,
>
> Here's two KCSAN cleanups and the required noinstr change for x86.

Thank you!

Reviewed-by: Marco Elver <elver@google.com>

As promised, here are the patches that would take care of KASAN and
UBSAN, rebased on the patches here:
https://lkml.kernel.org/r/20200602184409.22142-1-elver@google.com

Thanks,
-- Marco