Commit 3df7b41a authored by Jan Beulich's avatar Jan Beulich Committed by Ingo Molnar
Browse files

x86: Unify copy_from_user() size checking 



Commits 4a312769 ("x86: Turn the
copy_from_user check into an (optional) compile time warning")
and 63312b6a ("x86: Add a
Kconfig option to turn the copy_from_user warnings into errors")
touched only the 32-bit variant of copy_from_user(), whereas the
original commit 9f0cf4ad ("x86:
Use __builtin_object_size() to validate the buffer size for
copy_from_user()") also added the same code to the 64-bit one.

Further the earlier conversion from an inline WARN() to the call
to copy_from_user_overflow() went a little too far: When the
number of bytes to be copied is not a constant (e.g. [looking at
3.11] in drivers/net/tun.c:__tun_chr_ioctl() or
drivers/pci/pcie/aer/aer_inject.c:aer_inject_write()), the
compiler will always have to keep the funtion call, and hence
there will always be a warning. By using __builtin_constant_p()
we can avoid this.

And then this slightly extends the effect of
CONFIG_DEBUG_STRICT_USER_COPY_CHECKS in that apart from
converting warnings to errors in the constant size case, it
retains the (possibly wrong) warnings in the non-constant size
case, such that if someone is prepared to get a few false
positives, (s)he'll be able to recover the current behavior
(except that these diagnostics now will never be converted to
errors).

Since the 32-bit variant (intentionally) didn't call
might_fault(), the unification results in this being called
twice now. Adding a suitable #ifdef would be the alternative if
that's a problem.

I'd like to point out though that with
__compiletime_object_size() being restricted to gcc before 4.6,
the whole construct is going to become more and more pointless
going forward. I would question however that commit
2fb0815c ("gcc4: disable
__compiletime_object_size for GCC 4.6+") was really necessary,
and instead this should have been dealt with as is done here
from the beginning.

Signed-off-by: default avatarJan Beulich <jbeulich@suse.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/5265056D02000078000FC4F3@nat28.tlf.novell.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 88829dfe

arch/x86/include/asm/uaccess.h

+68 −0
Original line number Diff line number Diff line
@@ -542,5 +542,73 @@ extern struct movsl_mask { 
# include <asm/uaccess_64.h>

#endif



unsigned long __must_check _copy_from_user(void *to, const void __user *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);



#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()



#else



static inline void

__copy_from_user_overflow(int size, unsigned long count)

{

	WARN(1, "Buffer overflow detected (%d < %lu)!\n", size, count);

}



#endif



static inline unsigned long __must_check

copy_from_user(void *to, const void __user *from, unsigned long n)

{

	int sz = __compiletime_object_size(to);



	might_fault();



	/*

	 * 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))

		n = _copy_from_user(to, from, n);

	else if(__builtin_constant_p(n))

		copy_from_user_overflow();

	else

		__copy_from_user_overflow(sz, n);



	return n;

}



#undef __copy_from_user_overflow



#endif /* _ASM_X86_UACCESS_H */

arch/x86/include/asm/uaccess_32.h

+0 −26
Original line number Diff line number Diff line
@@ -186,31 +186,5 @@ __copy_from_user_inatomic_nocache(void *to, const void __user *from, 


unsigned long __must_check copy_to_user(void __user *to,

					const void *from, unsigned long n);

unsigned long __must_check _copy_from_user(void *to,

					  const void __user *from,

					  unsigned long n);





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

;



static inline unsigned long __must_check copy_from_user(void *to,

					  const void __user *from,

					  unsigned long n)

{

	int sz = __compiletime_object_size(to);



	if (likely(sz == -1 || sz >= n))

		n = _copy_from_user(to, from, n);

	else

		copy_from_user_overflow();



	return n;

}



#endif /* _ASM_X86_UACCESS_32_H */

arch/x86/include/asm/uaccess_64.h

+0 −18
Original line number Diff line number Diff line
@@ -48,26 +48,8 @@ copy_user_generic(void *to, const void *from, unsigned len) 
__must_check unsigned long

_copy_to_user(void __user *to, const void *from, unsigned len);

__must_check unsigned long

_copy_from_user(void *to, const void __user *from, unsigned len);

__must_check unsigned long

copy_in_user(void __user *to, const void __user *from, unsigned len);



static inline unsigned long __must_check copy_from_user(void *to,

					  const void __user *from,

					  unsigned long n)

{

	int sz = __compiletime_object_size(to);



	might_fault();

	if (likely(sz == -1 || sz >= n))

		n = _copy_from_user(to, from, n);

#ifdef CONFIG_DEBUG_VM

	else

		WARN(1, "Buffer overflow detected!\n");

#endif

	return n;

}



static __always_inline __must_check

int copy_to_user(void __user *dst, const void *src, unsigned size)

{

arch/x86/lib/usercopy_32.c

+1 −2
Original line number Diff line number Diff line
@@ -679,8 +679,7 @@ EXPORT_SYMBOL(copy_to_user); 
 * If some data could not be copied, this function will pad the copied

 * data to the requested size using zero bytes.

 */

unsigned long

_copy_from_user(void *to, const void __user *from, unsigned long n)

unsigned long _copy_from_user(void *to, const void __user *from, unsigned n)

{

	if (access_ok(VERIFY_READ, from, n))

		n = __copy_from_user(to, from, n);