1 // SPDX-License-Identifier: GPL-2.0-only 2 3 #include <linux/uaccess.h> 4 #include <linux/kernel.h> 5 6 #include <asm/vsyscall.h> 7 8 #ifdef CONFIG_X86_64 9 bool copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size) 10 { 11 unsigned long vaddr = (unsigned long)unsafe_src; 12 13 /* 14 * Do not allow userspace addresses. This disallows 15 * normal userspace and the userspace guard page: 16 */ 17 if (vaddr < TASK_SIZE_MAX + PAGE_SIZE) 18 return false; 19 20 /* 21 * Reading from the vsyscall page may cause an unhandled fault in 22 * certain cases. Though it is at an address above TASK_SIZE_MAX, it is 23 * usually considered as a user space address. 24 */ 25 if (is_vsyscall_vaddr(vaddr)) 26 return false; 27 28 /* 29 * Allow everything during early boot before 'x86_virt_bits' 30 * is initialized. Needed for instruction decoding in early 31 * exception handlers. 32 */ 33 if (!boot_cpu_data.x86_virt_bits) 34 return true; 35 36 return __is_canonical_address(vaddr, boot_cpu_data.x86_virt_bits); 37 } 38 #else 39 bool copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size) 40 { 41 return (unsigned long)unsafe_src >= TASK_SIZE_MAX; 42 } 43 #endif 44