ARM: 9014/2: Replace string mem* functions for KASan

Functions like memset()/memmove()/memcpy() do a lot of memory
accesses.

If a bad pointer is passed to one of these functions it is important
to catch this. Compiler instrumentation cannot do this since these
functions are written in assembly.

KASan replaces these memory functions with instrumented variants.

The original functions are declared as weak symbols so that
the strong definitions in mm/kasan/kasan.c can replace them.

The original functions have aliases with a '__' prefix in their
name, so we can call the non-instrumented variant if needed.

We must use __memcpy()/__memset() in place of memcpy()/memset()
when we copy .data to RAM and when we clear .bss, because
kasan_early_init cannot be called before the initialization of
.data and .bss.

For the kernel compression and EFI libstub's custom string
libraries we need a special quirk: even if these are built
without KASan enabled, they rely on the global headers for their
custom string libraries, which means that e.g. memcpy()
will be defined to __memcpy() and we get link failures.
Since these implementations are written i C rather than
assembly we use e.g. __alias(memcpy) to redirected any
users back to the local implementation.

Cc: Andrey Ryabinin <[email protected]>
Cc: Alexander Potapenko <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: [email protected]
Reviewed-by: Ard Biesheuvel <[email protected]>
Tested-by: Ard Biesheuvel <[email protected]> # QEMU/KVM/mach-virt/LPAE/8G
Tested-by: Florian Fainelli <[email protected]> # Brahma SoCs
Tested-by: Ahmad Fatoum <[email protected]> # i.MX6Q
Reported-by: Russell King - ARM Linux <[email protected]>
Signed-off-by: Ahmad Fatoum <[email protected]>
Signed-off-by: Abbott Liu <[email protected]>
Signed-off-by: Florian Fainelli <[email protected]>
Signed-off-by: Linus Walleij <[email protected]>
Signed-off-by: Russell King <[email protected]>

Author: linusw

arch/arm/boot/compressed/string.c

@@ -7,6 +7,25 @@
 
 #include <linux/string.h>
 
+/*
+ * The decompressor is built without KASan but uses the same redirects as the
+ * rest of the kernel when CONFIG_KASAN is enabled, defining e.g. memcpy()
+ * to __memcpy() but since we are not linking with the main kernel string
+ * library in the decompressor, that will lead to link failures.
+ *
+ * Undefine KASan's versions, define the wrapped functions and alias them to
+ * the right names so that when e.g. __memcpy() appear in the code, it will
+ * still be linked to this local version of memcpy().
+ */
+#ifdef CONFIG_KASAN
+#undef memcpy
+#undef memmove
+#undef memset
+void *__memcpy(void *__dest, __const void *__src, size_t __n) __alias(memcpy);
+void *__memmove(void *__dest, __const void *__src, size_t count) __alias(memmove);
+void *__memset(void *s, int c, size_t count) __alias(memset);
+#endif
+
 void *memcpy(void *__dest, __const void *__src, size_t __n)
 {
 	int i = 0;

arch/arm/include/asm/string.h

@@ -5,6 +5,9 @@
 /*
  * We don't do inline string functions, since the
  * optimised inline asm versions are not small.
+ *
+ * The __underscore versions of some functions are for KASan to be able
+ * to replace them with instrumented versions.
  */
 
 #define __HAVE_ARCH_STRRCHR
@@ -15,15 +18,18 @@ extern char * strchr(const char * s, int c);
 
 #define __HAVE_ARCH_MEMCPY
 extern void * memcpy(void *, const void *, __kernel_size_t);
+extern void *__memcpy(void *dest, const void *src, __kernel_size_t n);
 
 #define __HAVE_ARCH_MEMMOVE
 extern void * memmove(void *, const void *, __kernel_size_t);
+extern void *__memmove(void *dest, const void *src, __kernel_size_t n);
 
 #define __HAVE_ARCH_MEMCHR
 extern void * memchr(const void *, int, __kernel_size_t);
 
 #define __HAVE_ARCH_MEMSET
 extern void * memset(void *, int, __kernel_size_t);
+extern void *__memset(void *s, int c, __kernel_size_t n);
 
 #define __HAVE_ARCH_MEMSET32
 extern void *__memset32(uint32_t *, uint32_t v, __kernel_size_t);
@@ -39,4 +45,24 @@ static inline void *memset64(uint64_t *p, uint64_t v, __kernel_size_t n)
 	return __memset64(p, v, n * 8, v >> 32);
 }
 
+/*
+ * For files that are not instrumented (e.g. mm/slub.c) we
+ * must use non-instrumented versions of the mem*
+ * functions named __memcpy() etc. All such kernel code has
+ * been tagged with KASAN_SANITIZE_file.o = n, which means
+ * that the address sanitization argument isn't passed to the
+ * compiler, and __SANITIZE_ADDRESS__ is not set. As a result
+ * these defines kick in.
+ */
+#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
+#define memcpy(dst, src, len) __memcpy(dst, src, len)
+#define memmove(dst, src, len) __memmove(dst, src, len)
+#define memset(s, c, n) __memset(s, c, n)
+
+#ifndef __NO_FORTIFY
+#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
+#endif
+
+#endif
+
 #endif

arch/arm/kernel/head-common.S

@@ -95,15 +95,15 @@ __mmap_switched:
  THUMB(	ldmia	r4!, {r0, r1, r2, r3} )
  THUMB(	mov	sp, r3 )
 	sub	r2, r2, r1
-	bl	memcpy				@ copy .data to RAM
+	bl	__memcpy			@ copy .data to RAM
 #endif
 
    ARM(	ldmia	r4!, {r0, r1, sp} )
  THUMB(	ldmia	r4!, {r0, r1, r3} )
  THUMB(	mov	sp, r3 )
 	sub	r2, r1, r0
 	mov	r1, #0
-	bl	memset				@ clear .bss
+	bl	__memset			@ clear .bss
 
 	ldmia	r4, {r0, r1, r2, r3}
 	str	r9, [r0]			@ Save processor ID

arch/arm/lib/memcpy.S

@@ -58,10 +58,13 @@
 
 /* Prototype: void *memcpy(void *dest, const void *src, size_t n); */
 
+.weak memcpy
+ENTRY(__memcpy)
 ENTRY(mmiocpy)
 ENTRY(memcpy)
 
 #include "copy_template.S"
 
 ENDPROC(memcpy)
 ENDPROC(mmiocpy)
+ENDPROC(__memcpy)

arch/arm/lib/memmove.S

@@ -24,12 +24,14 @@
  * occurring in the opposite direction.
  */
 
+.weak memmove
+ENTRY(__memmove)
 ENTRY(memmove)
 	UNWIND(	.fnstart			)
 
 		subs	ip, r0, r1
 		cmphi	r2, ip
-		bls	memcpy
+		bls	__memcpy
 
 		stmfd	sp!, {r0, r4, lr}
 	UNWIND(	.fnend				)
@@ -222,3 +224,4 @@ ENTRY(memmove)
 18:		backward_copy_shift	push=24	pull=8
 
 ENDPROC(memmove)
+ENDPROC(__memmove)

arch/arm/lib/memset.S

@@ -13,6 +13,8 @@
 	.text
 	.align	5
 
+.weak memset
+ENTRY(__memset)
 ENTRY(mmioset)
 ENTRY(memset)
 UNWIND( .fnstart         )
@@ -132,6 +134,7 @@ UNWIND( .fnstart            )
 UNWIND( .fnend   )
 ENDPROC(memset)
 ENDPROC(mmioset)
+ENDPROC(__memset)
 
 ENTRY(__memset32)
 UNWIND( .fnstart         )