Merge tag 'usercopy-v4.8-rc6-part2' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull more hardened usercopyfixes from Kees Cook:

 - force check_object_size() to be inline too

 - move page-spanning check behind a CONFIG since it's triggering false
   positives

[ Changed the page-spanning config option to depend on EXPERT in the
  merge.  That way it still gets build testing, and you can enable it if
  you want to, but is never enabled for "normal" configurations ]

* tag 'usercopy-v4.8-rc6-part2' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  usercopy: remove page-spanning test for now
  usercopy: force check_object_size() inline

3 files changed, 48 insertions, 28 deletions

diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
index 10c9e601398b..2b5b10eed74f 100644
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -118,8 +118,8 @@ static inline int arch_within_stack_frames(const void * const stack,
 extern void __check_object_size(const void *ptr, unsigned long n,
 					bool to_user);
 
-static inline void check_object_size(const void *ptr, unsigned long n,
-				     bool to_user)
+static __always_inline void check_object_size(const void *ptr, unsigned long n,
+					      bool to_user)
 {
 	if (!__builtin_constant_p(n))
 		__check_object_size(ptr, n, to_user);
diff --git a/mm/usercopy.c b/mm/usercopy.c
index a3cc3052f830..089328f2b920 100644
--- a/mm/usercopy.c
+++ b/mm/usercopy.c
@@ -134,31 +134,16 @@ static inline const char *check_bogus_address(const void *ptr, unsigned long n)
 	return NULL;
 }
 
-static inline const char *check_heap_object(const void *ptr, unsigned long n,
-					    bool to_user)
+/* Checks for allocs that are marked in some way as spanning multiple pages. */
+static inline const char *check_page_span(const void *ptr, unsigned long n,
+					  struct page *page, bool to_user)
 {
-	struct page *page, *endpage;
+#ifdef CONFIG_HARDENED_USERCOPY_PAGESPAN
 	const void *end = ptr + n - 1;
+	struct page *endpage;
 	bool is_reserved, is_cma;
 
 	/*
-	 * Some architectures (arm64) return true for virt_addr_valid() on
-	 * vmalloced addresses. Work around this by checking for vmalloc
-	 * first.
-	 */
-	if (is_vmalloc_addr(ptr))
-		return NULL;
-
-	if (!virt_addr_valid(ptr))
-		return NULL;
-
-	page = virt_to_head_page(ptr);
-
-	/* Check slab allocator for flags and size. */
-	if (PageSlab(page))
-		return __check_heap_object(ptr, n, page);
-
-	/*
 	 * Sometimes the kernel data regions are not marked Reserved (see
 	 * check below). And sometimes [_sdata,_edata) does not cover
 	 * rodata and/or bss, so check each range explicitly.
@@ -186,7 +171,7 @@ static inline const char *check_heap_object(const void *ptr, unsigned long n,
 		   ((unsigned long)end & (unsigned long)PAGE_MASK)))
 		return NULL;
 
-	/* Allow if start and end are inside the same compound page. */
+	/* Allow if fully inside the same compound (__GFP_COMP) page. */
 	endpage = virt_to_head_page(end);
 	if (likely(endpage == page))
 		return NULL;
@@ -199,20 +184,44 @@ static inline const char *check_heap_object(const void *ptr, unsigned long n,
 	is_reserved = PageReserved(page);
 	is_cma = is_migrate_cma_page(page);
 	if (!is_reserved && !is_cma)
-		goto reject;
+		return "<spans multiple pages>";
 
 	for (ptr += PAGE_SIZE; ptr <= end; ptr += PAGE_SIZE) {
 		page = virt_to_head_page(ptr);
 		if (is_reserved && !PageReserved(page))
-			goto reject;
+			return "<spans Reserved and non-Reserved pages>";
 		if (is_cma && !is_migrate_cma_page(page))
-			goto reject;
+			return "<spans CMA and non-CMA pages>";
 	}
+#endif
 
 	return NULL;
+}
+
+static inline const char *check_heap_object(const void *ptr, unsigned long n,
+					    bool to_user)
+{
+	struct page *page;
+
+	/*
+	 * Some architectures (arm64) return true for virt_addr_valid() on
+	 * vmalloced addresses. Work around this by checking for vmalloc
+	 * first.
+	 */
+	if (is_vmalloc_addr(ptr))
+		return NULL;
+
+	if (!virt_addr_valid(ptr))
+		return NULL;
+
+	page = virt_to_head_page(ptr);
+
+	/* Check slab allocator for flags and size. */
+	if (PageSlab(page))
+		return __check_heap_object(ptr, n, page);
 
-reject:
-	return "<spans multiple pages>";
+	/* Verify object does not incorrectly span multiple pages. */
+	return check_page_span(ptr, n, page, to_user);
 }
 
 /*
diff --git a/security/Kconfig b/security/Kconfig
index da10d9b573a4..118f4549404e 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -147,6 +147,17 @@ config HARDENED_USERCOPY
 	  or are part of the kernel text. This kills entire classes
 	  of heap overflow exploits and similar kernel memory exposures.
 
+config HARDENED_USERCOPY_PAGESPAN
+	bool "Refuse to copy allocations that span multiple pages"
+	depends on HARDENED_USERCOPY
+	depends on EXPERT
+	help
+	  When a multi-page allocation is done without __GFP_COMP,
+	  hardened usercopy will reject attempts to copy it. There are,
+	  however, several cases of this in the kernel that have not all
+	  been removed. This config is intended to be used only while
+	  trying to find such users.
+
 source security/selinux/Kconfig
 source security/smack/Kconfig
 source security/tomoyo/Kconfig