Commit 0d025d27 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Linus Torvalds

mm/usercopy: get rid of CONFIG_DEBUG_STRICT_USER_COPY_CHECKS

There are three usercopy warnings which are currently being silenced for
gcc 4.6 and newer:

1) "copy_from_user() buffer size is too small" compile warning/error

   This is a static warning which happens when object size and copy size
   are both const, and copy size > object size.  I didn't see any false
   positives for this one.  So the function warning attribute seems to
   be working fine here.

   Note this scenario is always a bug and so I think it should be
   changed to *always* be an error, regardless of
   CONFIG_DEBUG_STRICT_USER_COPY_CHECKS.

2) "copy_from_user() buffer size is not provably correct" compile warning

   This is another static warning which happens when I enable
   __compiletime_object_size() for new compilers (and
   CONFIG_DEBUG_STRICT_USER_COPY_CHECKS).  It happens when object size
   is const, but copy size is *not*.  In this case there's no way to
   compare the two at build time, so it gives the warning.  (Note the
   warning is a byproduct of the fact that gcc has no way of knowing
   whether the overflow function will be called, so the call isn't dead
   code and the warning attribute is activated.)

   So this warning seems to only indicate "this is an unusual pattern,
   maybe you should check it out" rather than "this is a bug".

   I get 102(!) of these warnings with allyesconfig and the
   __compiletime_object_size() gcc check removed.  I don't know if there
   are any real bugs hiding in there, but from looking at a small
   sample, I didn't see any.  According to Kees, it does sometimes find
   real bugs.  But the false positive rate seems high.

3) "Buffer overflow detected" runtime warning

   This is a runtime warning where object size is const, and copy size >
   object size.

All three warnings (both static and runtime) were completely disabled
for gcc 4.6 with the following commit:

  2fb0815c ("gcc4: disable __compiletime_object_size for GCC 4.6+")

That commit mistakenly assumed that the false positives were caused by a
gcc bug in __compiletime_object_size().  But in fact,
__compiletime_object_size() seems to be working fine.  The false
positives were instead triggered by #2 above.  (Though I don't have an
explanation for why the warnings supposedly only started showing up in
gcc 4.6.)

So remove warning #2 to get rid of all the false positives, and re-enable
warnings #1 and #3 by reverting the above commit.

Furthermore, since #1 is a real bug which is detected at compile time,
upgrade it to always be an error.

Having done all that, CONFIG_DEBUG_STRICT_USER_COPY_CHECKS is no longer
needed.
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Byungchul Park <byungchul.park@lge.com>
Cc: Nilay Vaish <nilayvaish@gmail.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d8dc020c
config PARISC
def_bool y
select ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS
select ARCH_MIGHT_HAVE_PC_PARPORT
select HAVE_IDE
select HAVE_OPROFILE
......
......@@ -245,7 +245,6 @@ CONFIG_DEBUG_RT_MUTEXES=y
CONFIG_PROVE_RCU_DELAY=y
CONFIG_DEBUG_BLOCK_EXT_DEVT=y
CONFIG_LATENCYTOP=y
CONFIG_DEBUG_STRICT_USER_COPY_CHECKS=y
CONFIG_KEYS=y
# CONFIG_CRYPTO_HW is not set
CONFIG_FONTS=y
......@@ -291,7 +291,6 @@ CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC=y
CONFIG_BOOTPARAM_HUNG_TASK_PANIC=y
# CONFIG_SCHED_DEBUG is not set
CONFIG_TIMER_STATS=y
CONFIG_DEBUG_STRICT_USER_COPY_CHECKS=y
CONFIG_CRYPTO_MANAGER=y
CONFIG_CRYPTO_ECB=m
CONFIG_CRYPTO_PCBC=m
......
......@@ -208,13 +208,13 @@ unsigned long copy_in_user(void __user *dst, const void __user *src, unsigned lo
#define __copy_to_user_inatomic __copy_to_user
#define __copy_from_user_inatomic __copy_from_user
extern void copy_from_user_overflow(void)
#ifdef CONFIG_DEBUG_STRICT_USER_COPY_CHECKS
__compiletime_error("copy_from_user() buffer size is not provably correct")
#else
__compiletime_warning("copy_from_user() buffer size is not provably correct")
#endif
;
extern void __compiletime_error("usercopy buffer size is too small")
__bad_copy_user(void);
static inline void copy_user_overflow(int size, unsigned long count)
{
WARN(1, "Buffer overflow detected (%d < %lu)!\n", size, count);
}
static inline unsigned long __must_check copy_from_user(void *to,
const void __user *from,
......@@ -223,10 +223,12 @@ static inline unsigned long __must_check copy_from_user(void *to,
int sz = __compiletime_object_size(to);
int ret = -EFAULT;
if (likely(sz == -1 || !__builtin_constant_p(n) || sz >= n))
if (likely(sz == -1 || sz >= n))
ret = __copy_from_user(to, from, n);
else
copy_from_user_overflow();
else if (!__builtin_constant_p(n))
copy_user_overflow(sz, n);
else
__bad_copy_user();
return ret;
}
......
......@@ -68,7 +68,6 @@ config DEBUG_RODATA
config S390
def_bool y
select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
select ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS
select ARCH_HAS_DEVMEM_IS_ALLOWED
select ARCH_HAS_ELF_RANDOMIZE
select ARCH_HAS_GCOV_PROFILE_ALL
......
......@@ -602,7 +602,6 @@ CONFIG_FAIL_FUTEX=y
CONFIG_FAULT_INJECTION_DEBUG_FS=y
CONFIG_FAULT_INJECTION_STACKTRACE_FILTER=y
CONFIG_LATENCYTOP=y
CONFIG_DEBUG_STRICT_USER_COPY_CHECKS=y
CONFIG_IRQSOFF_TRACER=y
CONFIG_PREEMPT_TRACER=y
CONFIG_SCHED_TRACER=y
......
......@@ -552,7 +552,6 @@ CONFIG_NOTIFIER_ERROR_INJECTION=m
CONFIG_CPU_NOTIFIER_ERROR_INJECT=m
CONFIG_PM_NOTIFIER_ERROR_INJECT=m
CONFIG_LATENCYTOP=y
CONFIG_DEBUG_STRICT_USER_COPY_CHECKS=y
CONFIG_BLK_DEV_IO_TRACE=y
# CONFIG_KPROBE_EVENT is not set
CONFIG_TRACE_ENUM_MAP_FILE=y
......
......@@ -549,7 +549,6 @@ CONFIG_TIMER_STATS=y
CONFIG_RCU_TORTURE_TEST=m
CONFIG_RCU_CPU_STALL_TIMEOUT=60
CONFIG_LATENCYTOP=y
CONFIG_DEBUG_STRICT_USER_COPY_CHECKS=y
CONFIG_SCHED_TRACER=y
CONFIG_FTRACE_SYSCALLS=y
CONFIG_STACK_TRACER=y
......
......@@ -172,7 +172,6 @@ CONFIG_DEBUG_NOTIFIERS=y
CONFIG_RCU_CPU_STALL_TIMEOUT=60
CONFIG_RCU_TRACE=y
CONFIG_LATENCYTOP=y
CONFIG_DEBUG_STRICT_USER_COPY_CHECKS=y
CONFIG_SCHED_TRACER=y
CONFIG_FTRACE_SYSCALLS=y
CONFIG_TRACER_SNAPSHOT_PER_CPU_SWAP=y
......
......@@ -311,6 +311,14 @@ int __get_user_bad(void) __attribute__((noreturn));
#define __put_user_unaligned __put_user
#define __get_user_unaligned __get_user
extern void __compiletime_error("usercopy buffer size is too small")
__bad_copy_user(void);
static inline void copy_user_overflow(int size, unsigned long count)
{
WARN(1, "Buffer overflow detected (%d < %lu)!\n", size, count);
}
/**
* copy_to_user: - Copy a block of data into user space.
* @to: Destination address, in user space.
......@@ -332,12 +340,6 @@ copy_to_user(void __user *to, const void *from, unsigned long n)
return __copy_to_user(to, from, n);
}
void copy_from_user_overflow(void)
#ifdef CONFIG_DEBUG_STRICT_USER_COPY_CHECKS
__compiletime_warning("copy_from_user() buffer size is not provably correct")
#endif
;
/**
* copy_from_user: - Copy a block of data from user space.
* @to: Destination address, in kernel space.
......@@ -362,7 +364,10 @@ copy_from_user(void *to, const void __user *from, unsigned long n)
might_fault();
if (unlikely(sz != -1 && sz < n)) {
copy_from_user_overflow();
if (!__builtin_constant_p(n))
copy_user_overflow(sz, n);
else
__bad_copy_user();
return n;
}
return __copy_from_user(to, from, n);
......
......@@ -4,7 +4,6 @@
config TILE
def_bool y
select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
select ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS
select ARCH_HAS_DEVMEM_IS_ALLOWED
select ARCH_HAVE_NMI_SAFE_CMPXCHG
select ARCH_WANT_FRAME_POINTERS
......
......@@ -416,14 +416,13 @@ _copy_from_user(void *to, const void __user *from, unsigned long n)
return n;
}
#ifdef CONFIG_DEBUG_STRICT_USER_COPY_CHECKS
/*
* There are still unprovable places in the generic code as of 2.6.34, so this
* option is not really compatible with -Werror, which is more useful in
* general.
*/
extern void copy_from_user_overflow(void)
__compiletime_warning("copy_from_user() size is not provably correct");
extern void __compiletime_error("usercopy buffer size is too small")
__bad_copy_user(void);
static inline void copy_user_overflow(int size, unsigned long count)
{
WARN(1, "Buffer overflow detected (%d < %lu)!\n", size, count);
}
static inline unsigned long __must_check copy_from_user(void *to,
const void __user *from,
......@@ -433,14 +432,13 @@ static inline unsigned long __must_check copy_from_user(void *to,
if (likely(sz == -1 || sz >= n))
n = _copy_from_user(to, from, n);
else if (!__builtin_constant_p(n))
copy_user_overflow(sz, n);
else
copy_from_user_overflow();
__bad_copy_user();
return n;
}
#else
#define copy_from_user _copy_from_user
#endif
#ifdef __tilegx__
/**
......
......@@ -24,7 +24,6 @@ config X86
select ARCH_DISCARD_MEMBLOCK
select ARCH_HAS_ACPI_TABLE_UPGRADE if ACPI
select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
select ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS
select ARCH_HAS_DEVMEM_IS_ALLOWED
select ARCH_HAS_ELF_RANDOMIZE
select ARCH_HAS_FAST_MULTIPLIER
......
......@@ -697,43 +697,14 @@ unsigned long __must_check _copy_from_user(void *to, const void __user *from,
unsigned long __must_check _copy_to_user(void __user *to, const void *from,
unsigned n);
#ifdef CONFIG_DEBUG_STRICT_USER_COPY_CHECKS
# define copy_user_diag __compiletime_error
#else
# define copy_user_diag __compiletime_warning
#endif
extern void copy_user_diag("copy_from_user() buffer size is too small")
copy_from_user_overflow(void);
extern void copy_user_diag("copy_to_user() buffer size is too small")
copy_to_user_overflow(void) __asm__("copy_from_user_overflow");
#undef copy_user_diag
#ifdef CONFIG_DEBUG_STRICT_USER_COPY_CHECKS
extern void
__compiletime_warning("copy_from_user() buffer size is not provably correct")
__copy_from_user_overflow(void) __asm__("copy_from_user_overflow");
#define __copy_from_user_overflow(size, count) __copy_from_user_overflow()
extern void
__compiletime_warning("copy_to_user() buffer size is not provably correct")
__copy_to_user_overflow(void) __asm__("copy_from_user_overflow");
#define __copy_to_user_overflow(size, count) __copy_to_user_overflow()
#else
extern void __compiletime_error("usercopy buffer size is too small")
__bad_copy_user(void);
static inline void
__copy_from_user_overflow(int size, unsigned long count)
static inline void copy_user_overflow(int size, unsigned long count)
{
WARN(1, "Buffer overflow detected (%d < %lu)!\n", size, count);
}
#define __copy_to_user_overflow __copy_from_user_overflow
#endif
static inline unsigned long __must_check
copy_from_user(void *to, const void __user *from, unsigned long n)
{
......@@ -743,31 +714,13 @@ copy_from_user(void *to, const void __user *from, unsigned long n)
kasan_check_write(to, n);
/*
* While we would like to have the compiler do the checking for us
* even in the non-constant size case, any false positives there are
* a problem (especially when DEBUG_STRICT_USER_COPY_CHECKS, but even
* without - the [hopefully] dangerous looking nature of the warning
* would make people go look at the respecitive call sites over and
* over again just to find that there's no problem).
*
* And there are cases where it's just not realistic for the compiler
* to prove the count to be in range. For example when multiple call
* sites of a helper function - perhaps in different source files -
* all doing proper range checking, yet the helper function not doing
* so again.
*
* Therefore limit the compile time checking to the constant size
* case, and do only runtime checking for non-constant sizes.
*/
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))
copy_from_user_overflow();
} else if (!__builtin_constant_p(n))
copy_user_overflow(sz, n);
else
__copy_from_user_overflow(sz, n);
__bad_copy_user();
return n;
}
......@@ -781,21 +734,17 @@ 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)) {
check_object_size(from, n, true);
n = _copy_to_user(to, from, n);
} else if (__builtin_constant_p(n))
copy_to_user_overflow();
} else if (!__builtin_constant_p(n))
copy_user_overflow(sz, n);
else
__copy_to_user_overflow(sz, n);
__bad_copy_user();
return n;
}
#undef __copy_from_user_overflow
#undef __copy_to_user_overflow
/*
* We rely on the nested NMI work to allow atomic faults from the NMI path; the
* nested NMI paths are careful to preserve CR2.
......
......@@ -72,6 +72,7 @@ struct exception_table_entry
/* Returns 0 if exception not found and fixup otherwise. */
extern unsigned long search_exception_table(unsigned long);
/*
* architectures with an MMU should override these two
*/
......
......@@ -158,7 +158,7 @@
#define __compiler_offsetof(a, b) \
__builtin_offsetof(a, b)
#if GCC_VERSION >= 40100 && GCC_VERSION < 40600
#if GCC_VERSION >= 40100
# define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
#endif
......
......@@ -1686,24 +1686,6 @@ config LATENCYTOP
Enable this option if you want to use the LatencyTOP tool
to find out which userspace is blocking on what kernel operations.
config ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS
bool
config DEBUG_STRICT_USER_COPY_CHECKS
bool "Strict user copy size checks"
depends on ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS
depends on DEBUG_KERNEL && !TRACE_BRANCH_PROFILING
help
Enabling this option turns a certain set of sanity checks for user
copy operations into compile time failures.
The copy_from_user() etc checks are there to help test if there
are sufficient security checks on the length argument of
the copy operation, by having gcc prove that the argument is
within bounds.
If unsure, say N.
source kernel/trace/Kconfig
menu "Runtime Testing"
......
......@@ -24,7 +24,6 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
is_single_threaded.o plist.o decompress.o kobject_uevent.o \
earlycpio.o seq_buf.o nmi_backtrace.o nodemask.o
obj-$(CONFIG_ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS) += usercopy.o
lib-$(CONFIG_MMU) += ioremap.o
lib-$(CONFIG_SMP) += cpumask.o
lib-$(CONFIG_HAS_DMA) += dma-noop.o
......
#include <linux/export.h>
#include <linux/bug.h>
#include <linux/uaccess.h>
void copy_from_user_overflow(void)
{
WARN(1, "Buffer overflow detected!\n");
}
EXPORT_SYMBOL(copy_from_user_overflow);
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment