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Implements HARDENED_USERCOPY verification of copy_to_user/copy_from_user

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bounds checking for most architectures on SLAB and SLUB.
 -----BEGIN PGP SIGNATURE-----
 Version: GnuPG v1
 Comment: Kees Cook <kees@outflux.net>
 
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 =USIR
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Merge tag 'usercopy-v4.8' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull usercopy protection from Kees Cook:
 "Tbhis implements HARDENED_USERCOPY verification of copy_to_user and
  copy_from_user bounds checking for most architectures on SLAB and
  SLUB"

* tag 'usercopy-v4.8' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  mm: SLUB hardened usercopy support
  mm: SLAB hardened usercopy support
  s390/uaccess: Enable hardened usercopy
  sparc/uaccess: Enable hardened usercopy
  powerpc/uaccess: Enable hardened usercopy
  ia64/uaccess: Enable hardened usercopy
  arm64/uaccess: Enable hardened usercopy
  ARM: uaccess: Enable hardened usercopy
  x86/uaccess: Enable hardened usercopy
  mm: Hardened usercopy
  mm: Implement stack frame object validation
  mm: Add is_migrate_cma_page
This commit is contained in:
Linus Torvalds 2016-08-08 14:48:14 -07:00
commit 1eccfa090e
28 changed files with 555 additions and 22 deletions
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9
arch/Kconfig
View File

@ -461,6 +461,15 @@ config CC_STACKPROTECTOR_STRONG
endchoice
config HAVE_ARCH_WITHIN_STACK_FRAMES
bool
help
An architecture should select this if it can walk the kernel stack
frames to determine if an object is part of either the arguments
or local variables (i.e. that it excludes saved return addresses,
and similar) by implementing an inline arch_within_stack_frames(),
which is used by CONFIG_HARDENED_USERCOPY.
config HAVE_CONTEXT_TRACKING
bool
help

1
arch/arm/Kconfig
View File

@ -35,6 +35,7 @@ config ARM
select HARDIRQS_SW_RESEND
select HAVE_ARCH_AUDITSYSCALL if (AEABI && !OABI_COMPAT)
select HAVE_ARCH_BITREVERSE if (CPU_32v7M || CPU_32v7) && !CPU_32v6
select HAVE_ARCH_HARDENED_USERCOPY
select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL && !CPU_ENDIAN_BE32 && MMU
select HAVE_ARCH_KGDB if !CPU_ENDIAN_BE32 && MMU
select HAVE_ARCH_MMAP_RND_BITS if MMU

11
arch/arm/include/asm/uaccess.h
View File

@ -480,7 +480,10 @@ arm_copy_from_user(void *to, const void __user *from, unsigned long n);
static inline unsigned long __must_check
__copy_from_user(void *to, const void __user *from, unsigned long n)
{
unsigned int __ua_flags = uaccess_save_and_enable();
unsigned int __ua_flags;
check_object_size(to, n, false);
__ua_flags = uaccess_save_and_enable();
n = arm_copy_from_user(to, from, n);
uaccess_restore(__ua_flags);
return n;
@ -495,11 +498,15 @@ static inline unsigned long __must_check
__copy_to_user(void __user *to, const void *from, unsigned long n)
{
#ifndef CONFIG_UACCESS_WITH_MEMCPY
unsigned int __ua_flags = uaccess_save_and_enable();
unsigned int __ua_flags;
check_object_size(from, n, true);
__ua_flags = uaccess_save_and_enable();
n = arm_copy_to_user(to, from, n);
uaccess_restore(__ua_flags);
return n;
#else
check_object_size(from, n, true);
return arm_copy_to_user(to, from, n);
#endif
}

1
arch/arm64/Kconfig
View File

@ -54,6 +54,7 @@ config ARM64
select HAVE_ALIGNED_STRUCT_PAGE if SLUB
select HAVE_ARCH_AUDITSYSCALL
select HAVE_ARCH_BITREVERSE
select HAVE_ARCH_HARDENED_USERCOPY
select HAVE_ARCH_HUGE_VMAP
select HAVE_ARCH_JUMP_LABEL
select HAVE_ARCH_KASAN if SPARSEMEM_VMEMMAP && !(ARM64_16K_PAGES && ARM64_VA_BITS_48)

15
arch/arm64/include/asm/uaccess.h
View File

@ -265,22 +265,25 @@ extern unsigned long __must_check __clear_user(void __user *addr, unsigned long
static inline unsigned long __must_check __copy_from_user(void *to, const void __user *from, unsigned long n)
{
kasan_check_write(to, n);
return __arch_copy_from_user(to, from, n);
check_object_size(to, n, false);
return __arch_copy_from_user(to, from, n);
}
static inline unsigned long __must_check __copy_to_user(void __user *to, const void *from, unsigned long n)
{
kasan_check_read(from, n);
return __arch_copy_to_user(to, from, n);
check_object_size(from, n, true);
return __arch_copy_to_user(to, from, n);
}
static inline unsigned long __must_check copy_from_user(void *to, const void __user *from, unsigned long n)
{
kasan_check_write(to, n);
if (access_ok(VERIFY_READ, from, n))
if (access_ok(VERIFY_READ, from, n)) {
check_object_size(to, n, false);
n = __arch_copy_from_user(to, from, n);
else /* security hole - plug it */
} else /* security hole - plug it */
memset(to, 0, n);
return n;
}
@ -289,8 +292,10 @@ static inline unsigned long __must_check copy_to_user(void __user *to, const voi
{
kasan_check_read(from, n);
if (access_ok(VERIFY_WRITE, to, n))
if (access_ok(VERIFY_WRITE, to, n)) {
check_object_size(from, n, true);
n = __arch_copy_to_user(to, from, n);
}
return n;
}

1
arch/ia64/Kconfig
View File

@ -52,6 +52,7 @@ config IA64
select MODULES_USE_ELF_RELA
select ARCH_USE_CMPXCHG_LOCKREF
select HAVE_ARCH_AUDITSYSCALL
select HAVE_ARCH_HARDENED_USERCOPY
default y
help
The Itanium Processor Family is Intel's 64-bit successor to

18
arch/ia64/include/asm/uaccess.h
View File

@ -241,12 +241,18 @@ extern unsigned long __must_check __copy_user (void __user *to, const void __use
static inline unsigned long
__copy_to_user (void __user *to, const void *from, unsigned long count)
{
if (!__builtin_constant_p(count))
check_object_size(from, count, true);
return __copy_user(to, (__force void __user *) from, count);
}
static inline unsigned long
__copy_from_user (void *to, const void __user *from, unsigned long count)
{
if (!__builtin_constant_p(count))
check_object_size(to, count, false);
return __copy_user((__force void __user *) to, from, count);
}
@ -258,8 +264,11 @@ __copy_from_user (void *to, const void __user *from, unsigned long count)
const void *__cu_from = (from); \
long __cu_len = (n); \
\
if (__access_ok(__cu_to, __cu_len, get_fs())) \
__cu_len = __copy_user(__cu_to, (__force void __user *) __cu_from, __cu_len); \
if (__access_ok(__cu_to, __cu_len, get_fs())) { \
if (!__builtin_constant_p(n)) \
check_object_size(__cu_from, __cu_len, true); \
__cu_len = __copy_user(__cu_to, (__force void __user *) __cu_from, __cu_len); \
} \
__cu_len; \
})
@ -270,8 +279,11 @@ __copy_from_user (void *to, const void __user *from, unsigned long count)
long __cu_len = (n); \
\
__chk_user_ptr(__cu_from); \
if (__access_ok(__cu_from, __cu_len, get_fs())) \
if (__access_ok(__cu_from, __cu_len, get_fs())) { \
if (!__builtin_constant_p(n)) \
check_object_size(__cu_to, __cu_len, false); \
__cu_len = __copy_user((__force void __user *) __cu_to, __cu_from, __cu_len); \
} \
__cu_len; \
})

1
arch/powerpc/Kconfig
View File

@ -166,6 +166,7 @@ config PPC
select HAVE_LIVEPATCH if HAVE_DYNAMIC_FTRACE_WITH_REGS
select GENERIC_CPU_AUTOPROBE
select HAVE_VIRT_CPU_ACCOUNTING
select HAVE_ARCH_HARDENED_USERCOPY
config GENERIC_CSUM
def_bool CPU_LITTLE_ENDIAN

21
arch/powerpc/include/asm/uaccess.h
View File

@ -310,10 +310,15 @@ static inline unsigned long copy_from_user(void *to,
{
unsigned long over;
if (access_ok(VERIFY_READ, from, n))
if (access_ok(VERIFY_READ, from, n)) {
if (!__builtin_constant_p(n))
check_object_size(to, n, false);
return __copy_tofrom_user((__force void __user *)to, from, n);
}
if ((unsigned long)from < TASK_SIZE) {
over = (unsigned long)from + n - TASK_SIZE;
if (!__builtin_constant_p(n - over))
check_object_size(to, n - over, false);
return __copy_tofrom_user((__force void __user *)to, from,
n - over) + over;
}
@ -325,10 +330,15 @@ static inline unsigned long copy_to_user(void __user *to,
{
unsigned long over;
if (access_ok(VERIFY_WRITE, to, n))
if (access_ok(VERIFY_WRITE, to, n)) {
if (!__builtin_constant_p(n))
check_object_size(from, n, true);
return __copy_tofrom_user(to, (__force void __user *)from, n);
}
if ((unsigned long)to < TASK_SIZE) {
over = (unsigned long)to + n - TASK_SIZE;
if (!__builtin_constant_p(n))
check_object_size(from, n - over, true);
return __copy_tofrom_user(to, (__force void __user *)from,
n - over) + over;
}
@ -372,6 +382,10 @@ static inline unsigned long __copy_from_user_inatomic(void *to,
if (ret == 0)
return 0;
}
if (!__builtin_constant_p(n))
check_object_size(to, n, false);
return __copy_tofrom_user((__force void __user *)to, from, n);
}
@ -398,6 +412,9 @@ static inline unsigned long __copy_to_user_inatomic(void __user *to,
if (ret == 0)
return 0;
}
if (!__builtin_constant_p(n))
check_object_size(from, n, true);
return __copy_tofrom_user(to, (__force const void __user *)from, n);
}

1
arch/s390/Kconfig
View File

@ -123,6 +123,7 @@ config S390
select HAVE_ALIGNED_STRUCT_PAGE if SLUB
select HAVE_ARCH_AUDITSYSCALL
select HAVE_ARCH_EARLY_PFN_TO_NID
select HAVE_ARCH_HARDENED_USERCOPY
select HAVE_ARCH_JUMP_LABEL
select CPU_NO_EFFICIENT_FFS if !HAVE_MARCH_Z9_109_FEATURES
select HAVE_ARCH_SECCOMP_FILTER

2
arch/s390/lib/uaccess.c
View File

@ -104,6 +104,7 @@ static inline unsigned long copy_from_user_mvcp(void *x, const void __user *ptr,
unsigned long __copy_from_user(void *to, const void __user *from, unsigned long n)
{
check_object_size(to, n, false);
if (static_branch_likely(&have_mvcos))
return copy_from_user_mvcos(to, from, n);
return copy_from_user_mvcp(to, from, n);
@ -177,6 +178,7 @@ static inline unsigned long copy_to_user_mvcs(void __user *ptr, const void *x,
unsigned long __copy_to_user(void __user *to, const void *from, unsigned long n)
{
check_object_size(from, n, true);
if (static_branch_likely(&have_mvcos))
return copy_to_user_mvcos(to, from, n);
return copy_to_user_mvcs(to, from, n);

1
arch/sparc/Kconfig
View File

@ -43,6 +43,7 @@ config SPARC
select OLD_SIGSUSPEND
select ARCH_HAS_SG_CHAIN
select CPU_NO_EFFICIENT_FFS
select HAVE_ARCH_HARDENED_USERCOPY
config SPARC32
def_bool !64BIT

14
arch/sparc/include/asm/uaccess_32.h
View File

@ -248,22 +248,28 @@ unsigned long __copy_user(void __user *to, const void __user *from, unsigned lon
static inline unsigned long copy_to_user(void __user *to, const void *from, unsigned long n)
{
if (n && __access_ok((unsigned long) to, n))
if (n && __access_ok((unsigned long) to, n)) {
if (!__builtin_constant_p(n))
check_object_size(from, n, true);
return __copy_user(to, (__force void __user *) from, n);
else
} else
return n;
}
static inline unsigned long __copy_to_user(void __user *to, const void *from, unsigned long n)
{
if (!__builtin_constant_p(n))
check_object_size(from, n, true);
return __copy_user(to, (__force void __user *) from, n);
}
static inline unsigned long copy_from_user(void *to, const void __user *from, unsigned long n)
{
if (n && __access_ok((unsigned long) from, n))
if (n && __access_ok((unsigned long) from, n)) {
if (!__builtin_constant_p(n))
check_object_size(to, n, false);
return __copy_user((__force void __user *) to, from, n);
else
} else
return n;
}

11
arch/sparc/include/asm/uaccess_64.h
View File

@ -210,8 +210,12 @@ unsigned long copy_from_user_fixup(void *to, const void __user *from,
static inline unsigned long __must_check
copy_from_user(void *to, const void __user *from, unsigned long size)
{
unsigned long ret = ___copy_from_user(to, from, size);
unsigned long ret;
if (!__builtin_constant_p(size))
check_object_size(to, size, false);
ret = ___copy_from_user(to, from, size);
if (unlikely(ret))
ret = copy_from_user_fixup(to, from, size);
@ -227,8 +231,11 @@ unsigned long copy_to_user_fixup(void __user *to, const void *from,
static inline unsigned long __must_check
copy_to_user(void __user *to, const void *from, unsigned long size)
{
unsigned long ret = ___copy_to_user(to, from, size);
unsigned long ret;
if (!__builtin_constant_p(size))
check_object_size(from, size, true);
ret = ___copy_to_user(to, from, size);
if (unlikely(ret))
ret = copy_to_user_fixup(to, from, size);
return ret;

2
arch/x86/Kconfig
View File

@ -80,6 +80,7 @@ config X86
select HAVE_ALIGNED_STRUCT_PAGE if SLUB
select HAVE_AOUT if X86_32
select HAVE_ARCH_AUDITSYSCALL
select HAVE_ARCH_HARDENED_USERCOPY
select HAVE_ARCH_HUGE_VMAP if X86_64 || X86_PAE
select HAVE_ARCH_JUMP_LABEL
select HAVE_ARCH_KASAN if X86_64 && SPARSEMEM_VMEMMAP
@ -91,6 +92,7 @@ config X86
select HAVE_ARCH_SOFT_DIRTY if X86_64
select HAVE_ARCH_TRACEHOOK
select HAVE_ARCH_TRANSPARENT_HUGEPAGE
select HAVE_ARCH_WITHIN_STACK_FRAMES
select HAVE_EBPF_JIT if X86_64
select HAVE_CC_STACKPROTECTOR
select HAVE_CMPXCHG_DOUBLE

44
arch/x86/include/asm/thread_info.h
View File

@ -176,6 +176,50 @@ static inline unsigned long current_stack_pointer(void)
return sp;
}
/*
* Walks up the stack frames to make sure that the specified object is
* entirely contained by a single stack frame.
*
* Returns:
* 1 if within a frame
* -1 if placed across a frame boundary (or outside stack)
* 0 unable to determine (no frame pointers, etc)
*/
static inline int arch_within_stack_frames(const void * const stack,
const void * const stackend,
const void *obj, unsigned long len)
{
#if defined(CONFIG_FRAME_POINTER)
const void *frame = NULL;
const void *oldframe;
oldframe = __builtin_frame_address(1);
if (oldframe)
frame = __builtin_frame_address(2);
/*
* low ----------------------------------------------> high
* [saved bp][saved ip][args][local vars][saved bp][saved ip]
* ^----------------^
* allow copies only within here
*/
while (stack <= frame && frame < stackend) {
/*
* If obj + len extends past the last frame, this
* check won't pass and the next frame will be 0,
* causing us to bail out and correctly report
* the copy as invalid.
*/
if (obj + len <= frame)
return obj >= oldframe + 2 * sizeof(void *) ? 1 : -1;
oldframe = frame;
frame = *(const void * const *)frame;
}
return -1;
#else
return 0;
#endif
}
#else /* !__ASSEMBLY__ */
#ifdef CONFIG_X86_64

10
arch/x86/include/asm/uaccess.h
View File

@ -761,9 +761,10 @@ copy_from_user(void *to, const void __user *from, unsigned long n)
* case, and do only runtime checking for non-constant sizes.
*/
if (likely(sz < 0 || sz >= n))
if (likely(sz < 0 || sz >= n)) {
check_object_size(to, n, false);
n = _copy_from_user(to, from, n);
else if(__builtin_constant_p(n))
} else if (__builtin_constant_p(n))
copy_from_user_overflow();
else
__copy_from_user_overflow(sz, n);
@ -781,9 +782,10 @@ copy_to_user(void __user *to, const void *from, unsigned long n)
might_fault();
/* See the comment in copy_from_user() above. */
if (likely(sz < 0 || sz >= n))
if (likely(sz < 0 || sz >= n)) {
check_object_size(from, n, true);
n = _copy_to_user(to, from, n);
else if(__builtin_constant_p(n))
} else if (__builtin_constant_p(n))
copy_to_user_overflow();
else
__copy_to_user_overflow(sz, n);

2
arch/x86/include/asm/uaccess_32.h
View File

@ -37,6 +37,7 @@ unsigned long __must_check __copy_from_user_ll_nocache_nozero
static __always_inline unsigned long __must_check
__copy_to_user_inatomic(void __user *to, const void *from, unsigned long n)
{
check_object_size(from, n, true);
return __copy_to_user_ll(to, from, n);
}
@ -95,6 +96,7 @@ static __always_inline unsigned long
__copy_from_user(void *to, const void __user *from, unsigned long n)
{
might_fault();
check_object_size(to, n, false);
if (__builtin_constant_p(n)) {
unsigned long ret;

2
arch/x86/include/asm/uaccess_64.h
View File

@ -54,6 +54,7 @@ int __copy_from_user_nocheck(void *dst, const void __user *src, unsigned size)
{
int ret = 0;
check_object_size(dst, size, false);
if (!__builtin_constant_p(size))
return copy_user_generic(dst, (__force void *)src, size);
switch (size) {
@ -119,6 +120,7 @@ int __copy_to_user_nocheck(void __user *dst, const void *src, unsigned size)
{
int ret = 0;
check_object_size(src, size, true);
if (!__builtin_constant_p(size))
return copy_user_generic((__force void *)dst, src, size);
switch (size) {

2
include/linux/mmzone.h
View File

@ -68,8 +68,10 @@ extern char * const migratetype_names[MIGRATE_TYPES];
#ifdef CONFIG_CMA
# define is_migrate_cma(migratetype) unlikely((migratetype) == MIGRATE_CMA)
# define is_migrate_cma_page(_page) (get_pageblock_migratetype(_page) == MIGRATE_CMA)
#else
# define is_migrate_cma(migratetype) false
# define is_migrate_cma_page(_page) false
#endif
#define for_each_migratetype_order(order, type) \

12
include/linux/slab.h
View File

@ -155,6 +155,18 @@ void kfree(const void *);
void kzfree(const void *);
size_t ksize(const void *);
#ifdef CONFIG_HAVE_HARDENED_USERCOPY_ALLOCATOR
const char *__check_heap_object(const void *ptr, unsigned long n,
struct page *page);
#else
static inline const char *__check_heap_object(const void *ptr,
unsigned long n,
struct page *page)
{
return NULL;
}
#endif
/*
* Some archs want to perform DMA into kmalloc caches and need a guaranteed
* alignment larger than the alignment of a 64-bit integer.

24
include/linux/thread_info.h
View File

@ -105,6 +105,30 @@ static inline int test_ti_thread_flag(struct thread_info *ti, int flag)
#define tif_need_resched() test_thread_flag(TIF_NEED_RESCHED)
#ifndef CONFIG_HAVE_ARCH_WITHIN_STACK_FRAMES
static inline int arch_within_stack_frames(const void * const stack,
const void * const stackend,
const void *obj, unsigned long len)
{
return 0;
}
#endif
#ifdef CONFIG_HARDENED_USERCOPY
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)
{
__check_object_size(ptr, n, to_user);
}
#else
static inline void check_object_size(const void *ptr, unsigned long n,
bool to_user)
{ }
#endif /* CONFIG_HARDENED_USERCOPY */
#endif /* __KERNEL__ */
#endif /* _LINUX_THREAD_INFO_H */

2
init/Kconfig
View File

@ -1761,6 +1761,7 @@ choice
config SLAB
bool "SLAB"
select HAVE_HARDENED_USERCOPY_ALLOCATOR
help
The regular slab allocator that is established and known to work
well in all environments. It organizes cache hot objects in
@ -1768,6 +1769,7 @@ config SLAB
config SLUB
bool "SLUB (Unqueued Allocator)"
select HAVE_HARDENED_USERCOPY_ALLOCATOR
help
SLUB is a slab allocator that minimizes cache line usage
instead of managing queues of cached objects (SLAB approach).

4
mm/Makefile
View File

@ -21,6 +21,9 @@ KCOV_INSTRUMENT_memcontrol.o := n
KCOV_INSTRUMENT_mmzone.o := n
KCOV_INSTRUMENT_vmstat.o := n
# Since __builtin_frame_address does work as used, disable the warning.
CFLAGS_usercopy.o += $(call cc-disable-warning, frame-address)
mmu-y := nommu.o
mmu-$(CONFIG_MMU) := gup.o highmem.o memory.o mincore.o \
mlock.o mmap.o mprotect.o mremap.o msync.o rmap.o \
@ -99,3 +102,4 @@ obj-$(CONFIG_USERFAULTFD) += userfaultfd.o
obj-$(CONFIG_IDLE_PAGE_TRACKING) += page_idle.o
obj-$(CONFIG_FRAME_VECTOR) += frame_vector.o
obj-$(CONFIG_DEBUG_PAGE_REF) += debug_page_ref.o
obj-$(CONFIG_HARDENED_USERCOPY) += usercopy.o

30
mm/slab.c
View File

@ -4441,6 +4441,36 @@ static int __init slab_proc_init(void)
module_init(slab_proc_init);
#endif
#ifdef CONFIG_HARDENED_USERCOPY
/*
* Rejects objects that are incorrectly sized.
*
* Returns NULL if check passes, otherwise const char * to name of cache
* to indicate an error.
*/
const char *__check_heap_object(const void *ptr, unsigned long n,
struct page *page)
{
struct kmem_cache *cachep;
unsigned int objnr;
unsigned long offset;
/* Find and validate object. */
cachep = page->slab_cache;
objnr = obj_to_index(cachep, page, (void *)ptr);
BUG_ON(objnr >= cachep->num);
/* Find offset within object. */
offset = ptr - index_to_obj(cachep, page, objnr) - obj_offset(cachep);
/* Allow address range falling entirely within object size. */
if (offset <= cachep->object_size && n <= cachep->object_size - offset)
return NULL;
return cachep->name;
}
#endif /* CONFIG_HARDENED_USERCOPY */
/**
* ksize - get the actual amount of memory allocated for a given object
* @objp: Pointer to the object

40
mm/slub.c
View File

@ -3764,6 +3764,46 @@ void *__kmalloc_node(size_t size, gfp_t flags, int node)
EXPORT_SYMBOL(__kmalloc_node);
#endif
#ifdef CONFIG_HARDENED_USERCOPY
/*
* Rejects objects that are incorrectly sized.
*
* Returns NULL if check passes, otherwise const char * to name of cache
* to indicate an error.
*/
const char *__check_heap_object(const void *ptr, unsigned long n,
struct page *page)
{
struct kmem_cache *s;
unsigned long offset;
size_t object_size;
/* Find object and usable object size. */
s = page->slab_cache;
object_size = slab_ksize(s);
/* Reject impossible pointers. */
if (ptr < page_address(page))
return s->name;
/* Find offset within object. */
offset = (ptr - page_address(page)) % s->size;
/* Adjust for redzone and reject if within the redzone. */
if (kmem_cache_debug(s) && s->flags & SLAB_RED_ZONE) {
if (offset < s->red_left_pad)
return s->name;
offset -= s->red_left_pad;
}
/* Allow address range falling entirely within object size. */
if (offset <= object_size && n <= object_size - offset)
return NULL;
return s->name;
}
#endif /* CONFIG_HARDENED_USERCOPY */
static size_t __ksize(const void *object)
{
struct page *page;

268
mm/usercopy.c Normal file
View File

@ -0,0 +1,268 @@
/*
* This implements the various checks for CONFIG_HARDENED_USERCOPY*,
* which are designed to protect kernel memory from needless exposure
* and overwrite under many unintended conditions. This code is based
* on PAX_USERCOPY, which is:
*
* Copyright (C) 2001-2016 PaX Team, Bradley Spengler, Open Source
* Security Inc.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/mm.h>
#include <linux/slab.h>
#include <asm/sections.h>
enum {
BAD_STACK = -1,
NOT_STACK = 0,
GOOD_FRAME,
GOOD_STACK,
};
/*
* Checks if a given pointer and length is contained by the current
* stack frame (if possible).
*
* Returns:
* NOT_STACK: not at all on the stack
* GOOD_FRAME: fully within a valid stack frame
* GOOD_STACK: fully on the stack (when can't do frame-checking)
* BAD_STACK: error condition (invalid stack position or bad stack frame)
*/
static noinline int check_stack_object(const void *obj, unsigned long len)
{
const void * const stack = task_stack_page(current);
const void * const stackend = stack + THREAD_SIZE;
int ret;
/* Object is not on the stack at all. */
if (obj + len <= stack || stackend <= obj)
return NOT_STACK;
/*
* Reject: object partially overlaps the stack (passing the
* the check above means at least one end is within the stack,
* so if this check fails, the other end is outside the stack).
*/
if (obj < stack || stackend < obj + len)
return BAD_STACK;
/* Check if object is safely within a valid frame. */
ret = arch_within_stack_frames(stack, stackend, obj, len);
if (ret)
return ret;
return GOOD_STACK;
}
static void report_usercopy(const void *ptr, unsigned long len,
bool to_user, const char *type)
{
pr_emerg("kernel memory %s attempt detected %s %p (%s) (%lu bytes)\n",
to_user ? "exposure" : "overwrite",
to_user ? "from" : "to", ptr, type ? : "unknown", len);
/*
* For greater effect, it would be nice to do do_group_exit(),
* but BUG() actually hooks all the lock-breaking and per-arch
* Oops code, so that is used here instead.
*/
BUG();
}
/* Returns true if any portion of [ptr,ptr+n) over laps with [low,high). */
static bool overlaps(const void *ptr, unsigned long n, unsigned long low,
unsigned long high)
{
unsigned long check_low = (uintptr_t)ptr;
unsigned long check_high = check_low + n;
/* Does not overlap if entirely above or entirely below. */
if (check_low >= high || check_high < low)
return false;
return true;
}
/* Is this address range in the kernel text area? */
static inline const char *check_kernel_text_object(const void *ptr,
unsigned long n)
{
unsigned long textlow = (unsigned long)_stext;
unsigned long texthigh = (unsigned long)_etext;
unsigned long textlow_linear, texthigh_linear;
if (overlaps(ptr, n, textlow, texthigh))
return "<kernel text>";
/*
* Some architectures have virtual memory mappings with a secondary
* mapping of the kernel text, i.e. there is more than one virtual
* kernel address that points to the kernel image. It is usually
* when there is a separate linear physical memory mapping, in that
* __pa() is not just the reverse of __va(). This can be detected
* and checked:
*/
textlow_linear = (unsigned long)__va(__pa(textlow));
/* No different mapping: we're done. */
if (textlow_linear == textlow)
return NULL;
/* Check the secondary mapping... */
texthigh_linear = (unsigned long)__va(__pa(texthigh));
if (overlaps(ptr, n, textlow_linear, texthigh_linear))
return "<linear kernel text>";
return NULL;
}
static inline const char *check_bogus_address(const void *ptr, unsigned long n)
{
/* Reject if object wraps past end of memory. */
if (ptr + n < ptr)
return "<wrapped address>";
/* Reject if NULL or ZERO-allocation. */
if (ZERO_OR_NULL_PTR(ptr))
return "<null>";
return NULL;
}
static inline const char *check_heap_object(const void *ptr, unsigned long n,
bool to_user)
{
struct page *page, *endpage;
const void *end = ptr + n - 1;
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.
*/
/* Allow reads of kernel rodata region (if not marked as Reserved). */
if (ptr >= (const void *)__start_rodata &&
end <= (const void *)__end_rodata) {
if (!to_user)
return "<rodata>";
return NULL;
}
/* Allow kernel data region (if not marked as Reserved). */
if (ptr >= (const void *)_sdata && end <= (const void *)_edata)
return NULL;
/* Allow kernel bss region (if not marked as Reserved). */
if (ptr >= (const void *)__bss_start &&
end <= (const void *)__bss_stop)
return NULL;
/* Is the object wholly within one base page? */
if (likely(((unsigned long)ptr & (unsigned long)PAGE_MASK) ==
((unsigned long)end & (unsigned long)PAGE_MASK)))
return NULL;
/* Allow if start and end are inside the same compound page. */
endpage = virt_to_head_page(end);
if (likely(endpage == page))
return NULL;
/*
* Reject if range is entirely either Reserved (i.e. special or
* device memory), or CMA. Otherwise, reject since the object spans
* several independently allocated pages.
*/
is_reserved = PageReserved(page);
is_cma = is_migrate_cma_page(page);
if (!is_reserved && !is_cma)
goto reject;
for (ptr += PAGE_SIZE; ptr <= end; ptr += PAGE_SIZE) {
page = virt_to_head_page(ptr);
if (is_reserved && !PageReserved(page))
goto reject;
if (is_cma && !is_migrate_cma_page(page))
goto reject;
}
return NULL;
reject:
return "<spans multiple pages>";
}
/*
* Validates that the given object is:
* - not bogus address
* - known-safe heap or stack object
* - not in kernel text
*/
void __check_object_size(const void *ptr, unsigned long n, bool to_user)
{
const char *err;
/* Skip all tests if size is zero. */
if (!n)
return;
/* Check for invalid addresses. */
err = check_bogus_address(ptr, n);
if (err)
goto report;
/* Check for bad heap object. */
err = check_heap_object(ptr, n, to_user);
if (err)
goto report;
/* Check for bad stack object. */
switch (check_stack_object(ptr, n)) {
case NOT_STACK:
/* Object is not touching the current process stack. */
break;
case GOOD_FRAME:
case GOOD_STACK:
/*
* Object is either in the correct frame (when it
* is possible to check) or just generally on the
* process stack (when frame checking not available).
*/
return;
default:
err = "<process stack>";
goto report;
}
/* Check for object in kernel to avoid text exposure. */
err = check_kernel_text_object(ptr, n);
if (!err)
return;
report:
report_usercopy(ptr, n, to_user, err);
}
EXPORT_SYMBOL(__check_object_size);

28
security/Kconfig
View File

@ -118,6 +118,34 @@ config LSM_MMAP_MIN_ADDR
this low address space will need the permission specific to the
systems running LSM.
config HAVE_HARDENED_USERCOPY_ALLOCATOR
bool
help
The heap allocator implements __check_heap_object() for
validating memory ranges against heap object sizes in
support of CONFIG_HARDENED_USERCOPY.
config HAVE_ARCH_HARDENED_USERCOPY
bool
help
The architecture supports CONFIG_HARDENED_USERCOPY by
calling check_object_size() just before performing the
userspace copies in the low level implementation of
copy_to_user() and copy_from_user().
config HARDENED_USERCOPY
bool "Harden memory copies between kernel and userspace"
depends on HAVE_ARCH_HARDENED_USERCOPY
select BUG
help
This option checks for obviously wrong memory regions when
copying memory to/from the kernel (via copy_to_user() and
copy_from_user() functions) by rejecting memory ranges that
are larger than the specified heap object, span multiple
separately allocates pages, are not on the process stack,
or are part of the kernel text. This kills entire classes
of heap overflow exploits and similar kernel memory exposures.
source security/selinux/Kconfig
source security/smack/Kconfig
source security/tomoyo/Kconfig