root/arch/x86/kernel/sys_x86_64.c

DEFINITIONS

1. get_align_mask
2. get_align_bits
3. align_vdso_addr
4. control_va_addr_alignment
5. SYSCALL_DEFINE6
6. find_start_end
7. arch_get_unmapped_area
8. arch_get_unmapped_area_topdown

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/compat.h>
   3 #include <linux/errno.h>
   4 #include <linux/sched.h>
   5 #include <linux/sched/mm.h>
   6 #include <linux/syscalls.h>
   7 #include <linux/mm.h>
   8 #include <linux/fs.h>
   9 #include <linux/smp.h>
  10 #include <linux/sem.h>
  11 #include <linux/msg.h>
  12 #include <linux/shm.h>
  13 #include <linux/stat.h>
  14 #include <linux/mman.h>
  15 #include <linux/file.h>
  16 #include <linux/utsname.h>
  17 #include <linux/personality.h>
  18 #include <linux/random.h>
  19 #include <linux/uaccess.h>
  20 #include <linux/elf.h>
  21 
  22 #include <asm/elf.h>
  23 #include <asm/ia32.h>
  24 #include <asm/syscalls.h>
  25 #include <asm/mpx.h>
  26 
  27 /*
  28  * Align a virtual address to avoid aliasing in the I$ on AMD F15h.
  29  */
  30 static unsigned long get_align_mask(void)
  31 {
  32         /* handle 32- and 64-bit case with a single conditional */
  33         if (va_align.flags < 0 || !(va_align.flags & (2 - mmap_is_ia32())))
  34                 return 0;
  35 
  36         if (!(current->flags & PF_RANDOMIZE))
  37                 return 0;
  38 
  39         return va_align.mask;
  40 }
  41 
  42 /*
  43  * To avoid aliasing in the I$ on AMD F15h, the bits defined by the
  44  * va_align.bits, [12:upper_bit), are set to a random value instead of
  45  * zeroing them. This random value is computed once per boot. This form
  46  * of ASLR is known as "per-boot ASLR".
  47  *
  48  * To achieve this, the random value is added to the info.align_offset
  49  * value before calling vm_unmapped_area() or ORed directly to the
  50  * address.
  51  */
  52 static unsigned long get_align_bits(void)
  53 {
  54         return va_align.bits & get_align_mask();
  55 }
  56 
  57 unsigned long align_vdso_addr(unsigned long addr)
  58 {
  59         unsigned long align_mask = get_align_mask();
  60         addr = (addr + align_mask) & ~align_mask;
  61         return addr | get_align_bits();
  62 }
  63 
  64 static int __init control_va_addr_alignment(char *str)
  65 {
  66         /* guard against enabling this on other CPU families */
  67         if (va_align.flags < 0)
  68                 return 1;
  69 
  70         if (*str == 0)
  71                 return 1;
  72 
  73         if (*str == '=')
  74                 str++;
  75 
  76         if (!strcmp(str, "32"))
  77                 va_align.flags = ALIGN_VA_32;
  78         else if (!strcmp(str, "64"))
  79                 va_align.flags = ALIGN_VA_64;
  80         else if (!strcmp(str, "off"))
  81                 va_align.flags = 0;
  82         else if (!strcmp(str, "on"))
  83                 va_align.flags = ALIGN_VA_32 | ALIGN_VA_64;
  84         else
  85                 return 0;
  86 
  87         return 1;
  88 }
  89 __setup("align_va_addr", control_va_addr_alignment);
  90 
  91 SYSCALL_DEFINE6(mmap, unsigned long, addr, unsigned long, len,
  92                 unsigned long, prot, unsigned long, flags,
  93                 unsigned long, fd, unsigned long, off)
  94 {
  95         long error;
  96         error = -EINVAL;
  97         if (off & ~PAGE_MASK)
  98                 goto out;
  99 
 100         error = ksys_mmap_pgoff(addr, len, prot, flags, fd, off >> PAGE_SHIFT);
 101 out:
 102         return error;
 103 }
 104 
 105 static void find_start_end(unsigned long addr, unsigned long flags,
 106                 unsigned long *begin, unsigned long *end)
 107 {
 108         if (!in_32bit_syscall() && (flags & MAP_32BIT)) {
 109                 /* This is usually used needed to map code in small
 110                    model, so it needs to be in the first 31bit. Limit
 111                    it to that.  This means we need to move the
 112                    unmapped base down for this case. This can give
 113                    conflicts with the heap, but we assume that glibc
 114                    malloc knows how to fall back to mmap. Give it 1GB
 115                    of playground for now. -AK */
 116                 *begin = 0x40000000;
 117                 *end = 0x80000000;
 118                 if (current->flags & PF_RANDOMIZE) {
 119                         *begin = randomize_page(*begin, 0x02000000);
 120                 }
 121                 return;
 122         }
 123 
 124         *begin  = get_mmap_base(1);
 125         if (in_32bit_syscall())
 126                 *end = task_size_32bit();
 127         else
 128                 *end = task_size_64bit(addr > DEFAULT_MAP_WINDOW);
 129 }
 130 
 131 unsigned long
 132 arch_get_unmapped_area(struct file *filp, unsigned long addr,
 133                 unsigned long len, unsigned long pgoff, unsigned long flags)
 134 {
 135         struct mm_struct *mm = current->mm;
 136         struct vm_area_struct *vma;
 137         struct vm_unmapped_area_info info;
 138         unsigned long begin, end;
 139 
 140         addr = mpx_unmapped_area_check(addr, len, flags);
 141         if (IS_ERR_VALUE(addr))
 142                 return addr;
 143 
 144         if (flags & MAP_FIXED)
 145                 return addr;
 146 
 147         find_start_end(addr, flags, &begin, &end);
 148 
 149         if (len > end)
 150                 return -ENOMEM;
 151 
 152         if (addr) {
 153                 addr = PAGE_ALIGN(addr);
 154                 vma = find_vma(mm, addr);
 155                 if (end - len >= addr &&
 156                     (!vma || addr + len <= vm_start_gap(vma)))
 157                         return addr;
 158         }
 159 
 160         info.flags = 0;
 161         info.length = len;
 162         info.low_limit = begin;
 163         info.high_limit = end;
 164         info.align_mask = 0;
 165         info.align_offset = pgoff << PAGE_SHIFT;
 166         if (filp) {
 167                 info.align_mask = get_align_mask();
 168                 info.align_offset += get_align_bits();
 169         }
 170         return vm_unmapped_area(&info);
 171 }
 172 
 173 unsigned long
 174 arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
 175                           const unsigned long len, const unsigned long pgoff,
 176                           const unsigned long flags)
 177 {
 178         struct vm_area_struct *vma;
 179         struct mm_struct *mm = current->mm;
 180         unsigned long addr = addr0;
 181         struct vm_unmapped_area_info info;
 182 
 183         addr = mpx_unmapped_area_check(addr, len, flags);
 184         if (IS_ERR_VALUE(addr))
 185                 return addr;
 186 
 187         /* requested length too big for entire address space */
 188         if (len > TASK_SIZE)
 189                 return -ENOMEM;
 190 
 191         /* No address checking. See comment at mmap_address_hint_valid() */
 192         if (flags & MAP_FIXED)
 193                 return addr;
 194 
 195         /* for MAP_32BIT mappings we force the legacy mmap base */
 196         if (!in_32bit_syscall() && (flags & MAP_32BIT))
 197                 goto bottomup;
 198 
 199         /* requesting a specific address */
 200         if (addr) {
 201                 addr &= PAGE_MASK;
 202                 if (!mmap_address_hint_valid(addr, len))
 203                         goto get_unmapped_area;
 204 
 205                 vma = find_vma(mm, addr);
 206                 if (!vma || addr + len <= vm_start_gap(vma))
 207                         return addr;
 208         }
 209 get_unmapped_area:
 210 
 211         info.flags = VM_UNMAPPED_AREA_TOPDOWN;
 212         info.length = len;
 213         info.low_limit = PAGE_SIZE;
 214         info.high_limit = get_mmap_base(0);
 215 
 216         /*
 217          * If hint address is above DEFAULT_MAP_WINDOW, look for unmapped area
 218          * in the full address space.
 219          *
 220          * !in_32bit_syscall() check to avoid high addresses for x32
 221          * (and make it no op on native i386).
 222          */
 223         if (addr > DEFAULT_MAP_WINDOW && !in_32bit_syscall())
 224                 info.high_limit += TASK_SIZE_MAX - DEFAULT_MAP_WINDOW;
 225 
 226         info.align_mask = 0;
 227         info.align_offset = pgoff << PAGE_SHIFT;
 228         if (filp) {
 229                 info.align_mask = get_align_mask();
 230                 info.align_offset += get_align_bits();
 231         }
 232         addr = vm_unmapped_area(&info);
 233         if (!(addr & ~PAGE_MASK))
 234                 return addr;
 235         VM_BUG_ON(addr != -ENOMEM);
 236 
 237 bottomup:
 238         /*
 239          * A failed mmap() very likely causes application failure,
 240          * so fall back to the bottom-up function here. This scenario
 241          * can happen with large stack limits and large mmap()
 242          * allocations.
 243          */
 244         return arch_get_unmapped_area(filp, addr0, len, pgoff, flags);
 245 }