[PATCH v3 1/2] kcsan: Instrument memcpy/memset/memmove with newer Clang

[PATCH v3 1/2] kcsan: Instrument memcpy/memset/memmove with newer Clang

[Marco Elver]

With Clang version 16+, -fsanitize=thread will turn
memcpy/memset/memmove calls in instrumented functions into
__tsan_memcpy/__tsan_memset/__tsan_memmove calls respectively.

Add these functions to the core KCSAN runtime, so that we (a) catch data
races with mem* functions, and (b) won't run into linker errors with
such newer compilers.

Cc: stable@vger.kernel.org # v5.10+
Signed-off-by: Marco Elver <elver@google.com>
---
v3:
* Truncate sizes larger than MAX_ENCODABLE_SIZE, so we still set up
  watchpoints on them. Iterating through MAX_ENCODABLE_SIZE blocks may
  result in pathological cases where performance would seriously suffer.
  So let's avoid that for now.
* Just use memcpy/memset/memmove instead of __mem*() functions. Many
  architectures that already support KCSAN don't define them (mips,
  s390), and having both __mem* and mem versions of the functions
  provides little benefit elsewhere; and backporting would become more
  difficult, too. The compiler should not inline them given all
  parameters are non-constants here.

v2:
* Fix for architectures which do not provide their own
  memcpy/memset/memmove and instead use the generic versions in
  lib/string. In this case we'll just alias the __tsan_ variants.
---
 kernel/kcsan/core.c | 50 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
index fe12dfe254ec..54d077e1a2dc 100644
--- a/kernel/kcsan/core.c
+++ b/kernel/kcsan/core.c
@@ -14,10 +14,12 @@
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/list.h>
+#include <linux/minmax.h>
 #include <linux/moduleparam.h>
 #include <linux/percpu.h>
 #include <linux/preempt.h>
 #include <linux/sched.h>
+#include <linux/string.h>
 #include <linux/uaccess.h>
 
 #include "encoding.h"
@@ -1308,3 +1310,51 @@ noinline void __tsan_atomic_signal_fence(int memorder)
 	}
 }
 EXPORT_SYMBOL(__tsan_atomic_signal_fence);
+
+#ifdef __HAVE_ARCH_MEMSET
+void *__tsan_memset(void *s, int c, size_t count);
+noinline void *__tsan_memset(void *s, int c, size_t count)
+{
+	/*
+	 * Instead of not setting up watchpoints where accessed size is greater
+	 * than MAX_ENCODABLE_SIZE, truncate checked size to MAX_ENCODABLE_SIZE.
+	 */
+	size_t check_len = min_t(size_t, count, MAX_ENCODABLE_SIZE);
+
+	check_access(s, check_len, KCSAN_ACCESS_WRITE, _RET_IP_);
+	return memset(s, c, count);
+}
+#else
+void *__tsan_memset(void *s, int c, size_t count) __alias(memset);
+#endif
+EXPORT_SYMBOL(__tsan_memset);
+
+#ifdef __HAVE_ARCH_MEMMOVE
+void *__tsan_memmove(void *dst, const void *src, size_t len);
+noinline void *__tsan_memmove(void *dst, const void *src, size_t len)
+{
+	size_t check_len = min_t(size_t, len, MAX_ENCODABLE_SIZE);
+
+	check_access(dst, check_len, KCSAN_ACCESS_WRITE, _RET_IP_);
+	check_access(src, check_len, 0, _RET_IP_);
+	return memmove(dst, src, len);
+}
+#else
+void *__tsan_memmove(void *dst, const void *src, size_t len) __alias(memmove);
+#endif
+EXPORT_SYMBOL(__tsan_memmove);
+
+#ifdef __HAVE_ARCH_MEMCPY
+void *__tsan_memcpy(void *dst, const void *src, size_t len);
+noinline void *__tsan_memcpy(void *dst, const void *src, size_t len)
+{
+	size_t check_len = min_t(size_t, len, MAX_ENCODABLE_SIZE);
+
+	check_access(dst, check_len, KCSAN_ACCESS_WRITE, _RET_IP_);
+	check_access(src, check_len, 0, _RET_IP_);
+	return memcpy(dst, src, len);
+}
+#else
+void *__tsan_memcpy(void *dst, const void *src, size_t len) __alias(memcpy);
+#endif
+EXPORT_SYMBOL(__tsan_memcpy);
-- 
2.37.2.789.g6183377224-goog

[PATCH v3 2/2] objtool, kcsan: Add volatile read/write instrumentation to whitelist

[Marco Elver]

Adds KCSAN's volatile instrumentation to objtool's uaccess whitelist.

Recent kernel change have shown that this was missing from the uaccess
whitelist (since the first upstreamed version of KCSAN):

  mm/gup.o: warning: objtool: fault_in_readable+0x101: call to __tsan_volatile_write1() with UACCESS enabled

Fixes: 75d75b7a4d54 ("kcsan: Support distinguishing volatile accesses")
Signed-off-by: Marco Elver <elver@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
---
v2:
* Fix commit message.
---
 tools/objtool/check.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index e55fdf952a3a..67afdce3421f 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -999,6 +999,16 @@ static const char *uaccess_safe_builtin[] = {
 	"__tsan_read_write4",
 	"__tsan_read_write8",
 	"__tsan_read_write16",
+	"__tsan_volatile_read1",
+	"__tsan_volatile_read2",
+	"__tsan_volatile_read4",
+	"__tsan_volatile_read8",
+	"__tsan_volatile_read16",
+	"__tsan_volatile_write1",
+	"__tsan_volatile_write2",
+	"__tsan_volatile_write4",
+	"__tsan_volatile_write8",
+	"__tsan_volatile_write16",
 	"__tsan_atomic8_load",
 	"__tsan_atomic16_load",
 	"__tsan_atomic32_load",
-- 
2.37.2.789.g6183377224-goog

Re: [PATCH v3 1/2] kcsan: Instrument memcpy/memset/memmove with newer Clang

[Paul E. McKenney]

On Mon, Sep 12, 2022 at 11:45:40AM +0200, Marco Elver wrote:
> With Clang version 16+, -fsanitize=thread will turn
> memcpy/memset/memmove calls in instrumented functions into
> __tsan_memcpy/__tsan_memset/__tsan_memmove calls respectively.
> 
> Add these functions to the core KCSAN runtime, so that we (a) catch data
> races with mem* functions, and (b) won't run into linker errors with
> such newer compilers.
> 
> Cc: stable@vger.kernel.org # v5.10+
> Signed-off-by: Marco Elver <elver@google.com>

Queued and pushed, thank you!

							Thanx, Paul

> ---
> v3:
> * Truncate sizes larger than MAX_ENCODABLE_SIZE, so we still set up
>   watchpoints on them. Iterating through MAX_ENCODABLE_SIZE blocks may
>   result in pathological cases where performance would seriously suffer.
>   So let's avoid that for now.
> * Just use memcpy/memset/memmove instead of __mem*() functions. Many
>   architectures that already support KCSAN don't define them (mips,
>   s390), and having both __mem* and mem versions of the functions
>   provides little benefit elsewhere; and backporting would become more
>   difficult, too. The compiler should not inline them given all
>   parameters are non-constants here.
> 
> v2:
> * Fix for architectures which do not provide their own
>   memcpy/memset/memmove and instead use the generic versions in
>   lib/string. In this case we'll just alias the __tsan_ variants.
> ---
>  kernel/kcsan/core.c | 50 +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 50 insertions(+)
> 
> diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
> index fe12dfe254ec..54d077e1a2dc 100644
> --- a/kernel/kcsan/core.c
> +++ b/kernel/kcsan/core.c
> @@ -14,10 +14,12 @@
>  #include <linux/init.h>
>  #include <linux/kernel.h>
>  #include <linux/list.h>
> +#include <linux/minmax.h>
>  #include <linux/moduleparam.h>
>  #include <linux/percpu.h>
>  #include <linux/preempt.h>
>  #include <linux/sched.h>
> +#include <linux/string.h>
>  #include <linux/uaccess.h>
>  
>  #include "encoding.h"
> @@ -1308,3 +1310,51 @@ noinline void __tsan_atomic_signal_fence(int memorder)
>  	}
>  }
>  EXPORT_SYMBOL(__tsan_atomic_signal_fence);
> +
> +#ifdef __HAVE_ARCH_MEMSET
> +void *__tsan_memset(void *s, int c, size_t count);
> +noinline void *__tsan_memset(void *s, int c, size_t count)
> +{
> +	/*
> +	 * Instead of not setting up watchpoints where accessed size is greater
> +	 * than MAX_ENCODABLE_SIZE, truncate checked size to MAX_ENCODABLE_SIZE.
> +	 */
> +	size_t check_len = min_t(size_t, count, MAX_ENCODABLE_SIZE);
> +
> +	check_access(s, check_len, KCSAN_ACCESS_WRITE, _RET_IP_);
> +	return memset(s, c, count);
> +}
> +#else
> +void *__tsan_memset(void *s, int c, size_t count) __alias(memset);
> +#endif
> +EXPORT_SYMBOL(__tsan_memset);
> +
> +#ifdef __HAVE_ARCH_MEMMOVE
> +void *__tsan_memmove(void *dst, const void *src, size_t len);
> +noinline void *__tsan_memmove(void *dst, const void *src, size_t len)
> +{
> +	size_t check_len = min_t(size_t, len, MAX_ENCODABLE_SIZE);
> +
> +	check_access(dst, check_len, KCSAN_ACCESS_WRITE, _RET_IP_);
> +	check_access(src, check_len, 0, _RET_IP_);
> +	return memmove(dst, src, len);
> +}
> +#else
> +void *__tsan_memmove(void *dst, const void *src, size_t len) __alias(memmove);
> +#endif
> +EXPORT_SYMBOL(__tsan_memmove);
> +
> +#ifdef __HAVE_ARCH_MEMCPY
> +void *__tsan_memcpy(void *dst, const void *src, size_t len);
> +noinline void *__tsan_memcpy(void *dst, const void *src, size_t len)
> +{
> +	size_t check_len = min_t(size_t, len, MAX_ENCODABLE_SIZE);
> +
> +	check_access(dst, check_len, KCSAN_ACCESS_WRITE, _RET_IP_);
> +	check_access(src, check_len, 0, _RET_IP_);
> +	return memcpy(dst, src, len);
> +}
> +#else
> +void *__tsan_memcpy(void *dst, const void *src, size_t len) __alias(memcpy);
> +#endif
> +EXPORT_SYMBOL(__tsan_memcpy);
> -- 
> 2.37.2.789.g6183377224-goog
>