arch/x86/mm/maccess.c

   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