arch/x86/lib/kaslr.c

   1 /*
   2  * Entropy functions used on early boot for KASLR base and memory
   3  * randomization. The base randomization is done in the compressed
   4  * kernel and memory randomization is done early when the regular
   5  * kernel starts. This file is included in the compressed kernel and
   6  * normally linked in the regular.
   7  */
   8 #include <asm/kaslr.h>
   9 #include <asm/msr.h>
  10 #include <asm/archrandom.h>
  11 #include <asm/e820.h>
  12 #include <asm/io.h>
  13
  14 /*
  15  * When built for the regular kernel, several functions need to be stubbed out
  16  * or changed to their regular kernel equivalent.
  17  */
  18 #ifndef KASLR_COMPRESSED_BOOT
  19 #include <asm/cpufeature.h>
  20 #include <asm/setup.h>
  21
  22 #define debug_putstr(v) early_printk(v)
  23 #define has_cpuflag(f) boot_cpu_has(f)
  24 #define get_boot_seed() kaslr_offset()
  25 #endif
  26
  27 #define I8254_PORT_CONTROL      0x43
  28 #define I8254_PORT_COUNTER0     0x40
  29 #define I8254_CMD_READBACK      0xC0
  30 #define I8254_SELECT_COUNTER0   0x02
  31 #define I8254_STATUS_NOTREADY   0x40
  32 static inline u16 i8254(void)
  33 {
  34         u16 status, timer;
  35
  36         do {
  37                 outb(I8254_PORT_CONTROL,
  38                      I8254_CMD_READBACK | I8254_SELECT_COUNTER0);
  39                 status = inb(I8254_PORT_COUNTER0);
  40                 timer  = inb(I8254_PORT_COUNTER0);
  41                 timer |= inb(I8254_PORT_COUNTER0) << 8;
  42         } while (status & I8254_STATUS_NOTREADY);
  43
  44         return timer;
  45 }
  46
  47 unsigned long kaslr_get_random_long(const char *purpose)
  48 {
  49 #ifdef CONFIG_X86_64
  50         const unsigned long mix_const = 0x5d6008cbf3848dd3UL;
  51 #else
  52         const unsigned long mix_const = 0x3f39e593UL;
  53 #endif
  54         unsigned long raw, random = get_boot_seed();
  55         bool use_i8254 = true;
  56
  57         debug_putstr(purpose);
  58         debug_putstr(" KASLR using");
  59
  60         if (has_cpuflag(X86_FEATURE_RDRAND)) {
  61                 debug_putstr(" RDRAND");
  62                 if (rdrand_long(&raw)) {
  63                         random ^= raw;
  64                         use_i8254 = false;
  65                 }
  66         }
  67
  68         if (has_cpuflag(X86_FEATURE_TSC)) {
  69                 debug_putstr(" RDTSC");
  70                 raw = rdtsc();
  71
  72                 random ^= raw;
  73                 use_i8254 = false;
  74         }
  75
  76         if (use_i8254) {
  77                 debug_putstr(" i8254");
  78                 random ^= i8254();
  79         }
  80
  81         /* Circular multiply for better bit diffusion */
  82         asm("mul %3"
  83             : "=a" (random), "=d" (raw)
  84             : "a" (random), "rm" (mix_const));
  85         random += raw;
  86
  87         debug_putstr("...\n");
  88
  89         return random;
  90 }