1 /* 2 * User address space access functions. 3 * 4 * Copyright 1997 Andi Kleen <ak@muc.de> 5 * Copyright 1997 Linus Torvalds 6 * Copyright 2002 Andi Kleen <ak@suse.de> 7 */ 8 #include <linux/export.h> 9 #include <linux/uaccess.h> 10 11 /* 12 * Zero Userspace 13 */ 14 15 unsigned long __clear_user(void __user *addr, unsigned long size) 16 { 17 long __d0; 18 might_fault(); 19 /* no memory constraint because it doesn't change any memory gcc knows 20 about */ 21 stac(); 22 asm volatile( 23 " testq %[size8],%[size8]\n" 24 " jz 4f\n" 25 "0: movq %[zero],(%[dst])\n" 26 " addq %[eight],%[dst]\n" 27 " decl %%ecx ; jnz 0b\n" 28 "4: movq %[size1],%%rcx\n" 29 " testl %%ecx,%%ecx\n" 30 " jz 2f\n" 31 "1: movb %b[zero],(%[dst])\n" 32 " incq %[dst]\n" 33 " decl %%ecx ; jnz 1b\n" 34 "2:\n" 35 ".section .fixup,\"ax\"\n" 36 "3: lea 0(%[size1],%[size8],8),%[size8]\n" 37 " jmp 2b\n" 38 ".previous\n" 39 _ASM_EXTABLE(0b,3b) 40 _ASM_EXTABLE(1b,2b) 41 : [size8] "=&c"(size), [dst] "=&D" (__d0) 42 : [size1] "r"(size & 7), "[size8]" (size / 8), "[dst]"(addr), 43 [zero] "r" (0UL), [eight] "r" (8UL)); 44 clac(); 45 return size; 46 } 47 EXPORT_SYMBOL(__clear_user); 48 49 unsigned long clear_user(void __user *to, unsigned long n) 50 { 51 if (access_ok(VERIFY_WRITE, to, n)) 52 return __clear_user(to, n); 53 return n; 54 } 55 EXPORT_SYMBOL(clear_user); 56 57 /* 58 * Try to copy last bytes and clear the rest if needed. 59 * Since protection fault in copy_from/to_user is not a normal situation, 60 * it is not necessary to optimize tail handling. 61 */ 62 __visible unsigned long 63 copy_user_handle_tail(char *to, char *from, unsigned len) 64 { 65 for (; len; --len, to++) { 66 char c; 67 68 if (__get_user_nocheck(c, from++, sizeof(char))) 69 break; 70 if (__put_user_nocheck(c, to, sizeof(char))) 71 break; 72 } 73 clac(); 74 return len; 75 } 76