2022-09-09 07:54:12

by Marco Elver

Subject: [PATCH v2 2/3] kcsan: Instrument memcpy/memset/memmove with newer Clang

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: [email protected] # v5.10+
Signed-off-by: Marco Elver <[email protected]>
---
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 | 39 +++++++++++++++++++++++++++++++++++++++
1 file changed, 39 insertions(+)

diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
index fe12dfe254ec..4015f2a3e7f6 100644
--- a/kernel/kcsan/core.c
+++ b/kernel/kcsan/core.c
@@ -18,6 +18,7 @@
#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 +1309,41 @@ 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)
+{
+ check_access(s, count, 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)
+{
+ check_access(dst, len, KCSAN_ACCESS_WRITE, _RET_IP_);
+ check_access(src, 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)
+{
+ check_access(dst, len, KCSAN_ACCESS_WRITE, _RET_IP_);
+ check_access(src, 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

2022-09-09 08:42:20

by Dmitry Vyukov

Subject: Re: [PATCH v2 2/3] kcsan: Instrument memcpy/memset/memmove with newer Clang

On Fri, 9 Sept 2022 at 09:38, Marco Elver <[email protected]> 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: [email protected] # v5.10+
> Signed-off-by: Marco Elver <[email protected]>
> ---
> 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 | 39 +++++++++++++++++++++++++++++++++++++++
> 1 file changed, 39 insertions(+)
>
> diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
> index fe12dfe254ec..4015f2a3e7f6 100644
> --- a/kernel/kcsan/core.c
> +++ b/kernel/kcsan/core.c
> @@ -18,6 +18,7 @@
> #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 +1309,41 @@ 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)
> +{
> + check_access(s, count, KCSAN_ACCESS_WRITE, _RET_IP_);

These can use large sizes, does it make sense to truncate it to
MAX_ENCODABLE_SIZE?


> + 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)
> +{
> + check_access(dst, len, KCSAN_ACCESS_WRITE, _RET_IP_);
> + check_access(src, 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)
> +{
> + check_access(dst, len, KCSAN_ACCESS_WRITE, _RET_IP_);
> + check_access(src, 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
>

2022-09-09 08:52:29

by Marco Elver

Subject: Re: [PATCH v2 2/3] kcsan: Instrument memcpy/memset/memmove with newer Clang

On Fri, 9 Sept 2022 at 10:38, Dmitry Vyukov <[email protected]> wrote:
>
> On Fri, 9 Sept 2022 at 09:38, Marco Elver <[email protected]> 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: [email protected] # v5.10+
> > Signed-off-by: Marco Elver <[email protected]>
> > ---
> > 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 | 39 +++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 39 insertions(+)
> >
> > diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
> > index fe12dfe254ec..4015f2a3e7f6 100644
> > --- a/kernel/kcsan/core.c
> > +++ b/kernel/kcsan/core.c
> > @@ -18,6 +18,7 @@
> > #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 +1309,41 @@ 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)
> > +{
> > + check_access(s, count, KCSAN_ACCESS_WRITE, _RET_IP_);
>
> These can use large sizes, does it make sense to truncate it to
> MAX_ENCODABLE_SIZE?

Hmm, good point - that way it can still set up watchpoints on them.
I'll do a v3.