instrumented.h: add KMSAN support

To avoid false positives, KMSAN needs to unpoison the data copied from the
userspace.  To detect infoleaks - check the memory buffer passed to
copy_to_user().

Link: https://lkml.kernel.org/r/20220915150417.722975-19-glider@google.com
Signed-off-by: Alexander Potapenko <glider@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vegard Nossum <vegard.nossum@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/instrumented.h b/include/linux/instrumented.h
index 9f1dba8..501fa84 100644 (file)
--- a/include/linux/instrumented.h
+++ b/include/linux/instrumented.h
@@ -2,7 +2,7 @@
 
 /*
  * This header provides generic wrappers for memory access instrumentation that
- * the compiler cannot emit for: KASAN, KCSAN.
+ * the compiler cannot emit for: KASAN, KCSAN, KMSAN.
  */
 #ifndef _LINUX_INSTRUMENTED_H
 #define _LINUX_INSTRUMENTED_H
@@ -10,6 +10,7 @@
 #include <linux/compiler.h>
 #include <linux/kasan-checks.h>
 #include <linux/kcsan-checks.h>
+#include <linux/kmsan-checks.h>
 #include <linux/types.h>
 
 /**
@@ -117,6 +118,7 @@ instrument_copy_to_user(void __user *to, const void *from, unsigned long n)
 {
        kasan_check_read(from, n);
        kcsan_check_read(from, n);
+       kmsan_copy_to_user(to, from, n, 0);
 }
 
 /**
@@ -151,6 +153,7 @@ static __always_inline void
 instrument_copy_from_user_after(const void *to, const void __user *from,
                                unsigned long n, unsigned long left)
 {
+       kmsan_unpoison_memory(to, n - left);
 }
 
 /**
@@ -162,10 +165,14 @@ instrument_copy_from_user_after(const void *to, const void __user *from,
  *
  * @to destination variable, may not be address-taken
  */
-#define instrument_get_user(to)                         \
-({                                                      \
+#define instrument_get_user(to)                                \
+({                                                     \
+       u64 __tmp = (u64)(to);                          \
+       kmsan_unpoison_memory(&__tmp, sizeof(__tmp));   \
+       to = __tmp;                                     \
 })
 
+
 /**
  * instrument_put_user() - add instrumentation to put_user()-like macros
  *
@@ -177,8 +184,9 @@ instrument_copy_from_user_after(const void *to, const void __user *from,
  * @ptr userspace pointer to copy to
  * @size number of bytes to copy
  */
-#define instrument_put_user(from, ptr, size)                    \
-({                                                              \
+#define instrument_put_user(from, ptr, size)                   \
+({                                                             \
+       kmsan_copy_to_user(ptr, &from, sizeof(from), 0);        \
 })
 
 #endif /* _LINUX_INSTRUMENTED_H */

diff --git a/include/linux/kmsan-checks.h b/include/linux/kmsan-checks.h
index a6522a0..c4cae33 100644 (file)
--- a/include/linux/kmsan-checks.h
+++ b/include/linux/kmsan-checks.h
@@ -46,6 +46,21 @@ void kmsan_unpoison_memory(const void *address, size_t size);
  */
 void kmsan_check_memory(const void *address, size_t size);
 
+/**
+ * kmsan_copy_to_user() - Notify KMSAN about a data transfer to userspace.
+ * @to:      destination address in the userspace.
+ * @from:    source address in the kernel.
+ * @to_copy: number of bytes to copy.
+ * @left:    number of bytes not copied.
+ *
+ * If this is a real userspace data transfer, KMSAN checks the bytes that were
+ * actually copied to ensure there was no information leak. If @to belongs to
+ * the kernel space (which is possible for compat syscalls), KMSAN just copies
+ * the metadata.
+ */
+void kmsan_copy_to_user(void __user *to, const void *from, size_t to_copy,
+                       size_t left);
+
 #else
 
 static inline void kmsan_poison_memory(const void *address, size_t size,
@@ -58,6 +73,10 @@ static inline void kmsan_unpoison_memory(const void *address, size_t size)
 static inline void kmsan_check_memory(const void *address, size_t size)
 {
 }
+static inline void kmsan_copy_to_user(void __user *to, const void *from,
+                                     size_t to_copy, size_t left)
+{
+}
 
 #endif
 

diff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c
index 6f3e64b..5c0eb25 100644 (file)
--- a/mm/kmsan/hooks.c
+++ b/mm/kmsan/hooks.c
@@ -205,6 +205,44 @@ void kmsan_iounmap_page_range(unsigned long start, unsigned long end)
        kmsan_leave_runtime();
 }
 
+void kmsan_copy_to_user(void __user *to, const void *from, size_t to_copy,
+                       size_t left)
+{
+       unsigned long ua_flags;
+
+       if (!kmsan_enabled || kmsan_in_runtime())
+               return;
+       /*
+        * At this point we've copied the memory already. It's hard to check it
+        * before copying, as the size of actually copied buffer is unknown.
+        */
+
+       /* copy_to_user() may copy zero bytes. No need to check. */
+       if (!to_copy)
+               return;
+       /* Or maybe copy_to_user() failed to copy anything. */
+       if (to_copy <= left)
+               return;
+
+       ua_flags = user_access_save();
+       if ((u64)to < TASK_SIZE) {
+               /* This is a user memory access, check it. */
+               kmsan_internal_check_memory((void *)from, to_copy - left, to,
+                                           REASON_COPY_TO_USER);
+       } else {
+               /* Otherwise this is a kernel memory access. This happens when a
+                * compat syscall passes an argument allocated on the kernel
+                * stack to a real syscall.
+                * Don't check anything, just copy the shadow of the copied
+                * bytes.
+                */
+               kmsan_internal_memmove_metadata((void *)to, (void *)from,
+                                               to_copy - left);
+       }
+       user_access_restore(ua_flags);
+}
+EXPORT_SYMBOL(kmsan_copy_to_user);
+
 /* Functions from kmsan-checks.h follow. */
 void kmsan_poison_memory(const void *address, size_t size, gfp_t flags)
 {