Commit 1771c6e1 authored by Andrey Ryabinin's avatar Andrey Ryabinin Committed by Linus Torvalds
Browse files

x86/kasan: instrument user memory access API 

Exchange between user and kernel memory is coded in assembly language.
Which means that such accesses won't be spotted by KASAN as a compiler
instruments only C code.

Add explicit KASAN checks to user memory access API to ensure that
userspace writes to (or reads from) a valid kernel memory.

Note: Unlike others strncpy_from_user() is written mostly in C and KASAN
sees memory accesses in it.  However, it makes sense to add explicit
check for all @count bytes that *potentially* could be written to the
kernel.

[aryabinin@virtuozzo.com: move kasan check under the condition]
  Link: http://lkml.kernel.org/r/1462869209-21096-1-git-send-email-aryabinin@virtuozzo.com
Link: http://lkml.kernel.org/r/1462538722-1574-4-git-send-email-aryabinin@virtuozzo.com


Signed-off-by: default avatarAndrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 64f8ebaf

arch/x86/include/asm/uaccess.h

+5 −0
Original line number Diff line number Diff line
@@ -5,6 +5,7 @@ 
 */

#include <linux/errno.h>

#include <linux/compiler.h>

#include <linux/kasan-checks.h>

#include <linux/thread_info.h>

#include <linux/string.h>

#include <asm/asm.h>
@@ -721,6 +722,8 @@ copy_from_user(void *to, const void __user *from, unsigned long n) 


	might_fault();



	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
@@ -754,6 +757,8 @@ copy_to_user(void __user *to, const void *from, unsigned long n) 
{

	int sz = __compiletime_object_size(from);



	kasan_check_read(from, n);



	might_fault();



	/* See the comment in copy_from_user() above. */

arch/x86/include/asm/uaccess_64.h

+7 −0
Original line number Diff line number Diff line
@@ -7,6 +7,7 @@ 
#include <linux/compiler.h>

#include <linux/errno.h>

#include <linux/lockdep.h>

#include <linux/kasan-checks.h>

#include <asm/alternative.h>

#include <asm/cpufeatures.h>

#include <asm/page.h>
@@ -109,6 +110,7 @@ static __always_inline __must_check 
int __copy_from_user(void *dst, const void __user *src, unsigned size)

{

	might_fault();

	kasan_check_write(dst, size);

	return __copy_from_user_nocheck(dst, src, size);

}
@@ -175,6 +177,7 @@ static __always_inline __must_check 
int __copy_to_user(void __user *dst, const void *src, unsigned size)

{

	might_fault();

	kasan_check_read(src, size);

	return __copy_to_user_nocheck(dst, src, size);

}
@@ -242,12 +245,14 @@ int __copy_in_user(void __user *dst, const void __user *src, unsigned size) 
static __must_check __always_inline int

__copy_from_user_inatomic(void *dst, const void __user *src, unsigned size)

{

	kasan_check_write(dst, size);

	return __copy_from_user_nocheck(dst, src, size);

}



static __must_check __always_inline int

__copy_to_user_inatomic(void __user *dst, const void *src, unsigned size)

{

	kasan_check_read(src, size);

	return __copy_to_user_nocheck(dst, src, size);

}
@@ -258,6 +263,7 @@ static inline int 
__copy_from_user_nocache(void *dst, const void __user *src, unsigned size)

{

	might_fault();

	kasan_check_write(dst, size);

	return __copy_user_nocache(dst, src, size, 1);

}
@@ -265,6 +271,7 @@ static inline int 
__copy_from_user_inatomic_nocache(void *dst, const void __user *src,

				  unsigned size)

{

	kasan_check_write(dst, size);

	return __copy_user_nocache(dst, src, size, 0);

}

lib/strncpy_from_user.c

+2 −0
Original line number Diff line number Diff line 
#include <linux/compiler.h>

#include <linux/export.h>

#include <linux/kasan-checks.h>

#include <linux/uaccess.h>

#include <linux/kernel.h>

#include <linux/errno.h>
@@ -109,6 +110,7 @@ long strncpy_from_user(char *dst, const char __user *src, long count) 
		unsigned long max = max_addr - src_addr;

		long retval;



		kasan_check_write(dst, count);

		user_access_begin();

		retval = do_strncpy_from_user(dst, src, count, max);

		user_access_end();

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