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/asm.h>
   9 #include <asm/kaslr.h>
  10 #include <asm/msr.h>
  11 #include <asm/archrandom.h>
  12 #include <asm/e820/api.h>
  13 #include <asm/io.h>
  14
  15 /*
  16  * When built for the regular kernel, several functions need to be stubbed out
  17  * or changed to their regular kernel equivalent.
  18  */
  19 #ifndef KASLR_COMPRESSED_BOOT
  20 #include <asm/cpufeature.h>
  21 #include <asm/setup.h>
  22
  23 #define debug_putstr(v) early_printk("%s", v)
  24 #define has_cpuflag(f) boot_cpu_has(f)
  25 #define get_boot_seed() kaslr_offset()
  26 #endif
  27
  28 #define I8254_PORT_CONTROL      0x43
  29 #define I8254_PORT_COUNTER0     0x40
  30 #define I8254_CMD_READBACK      0xC0
  31 #define I8254_SELECT_COUNTER0   0x02
  32 #define I8254_STATUS_NOTREADY   0x40
  33 static inline u16 i8254(void)
  34 {
  35         u16 status, timer;
  36
  37         do {
  38                 outb(I8254_PORT_CONTROL,
  39                      I8254_CMD_READBACK | I8254_SELECT_COUNTER0);
  40                 status = inb(I8254_PORT_COUNTER0);
  41                 timer  = inb(I8254_PORT_COUNTER0);
  42                 timer |= inb(I8254_PORT_COUNTER0) << 8;
  43         } while (status & I8254_STATUS_NOTREADY);
  44
  45         return timer;
  46 }
  47
  48 unsigned long kaslr_get_random_long(const char *purpose)
  49 {
  50 #ifdef CONFIG_X86_64
  51         const unsigned long mix_const = 0x5d6008cbf3848dd3UL;
  52 #else
  53         const unsigned long mix_const = 0x3f39e593UL;
  54 #endif
  55         unsigned long raw, random = get_boot_seed();
  56         bool use_i8254 = true;
  57
  58         debug_putstr(purpose);
  59         debug_putstr(" KASLR using");
  60
  61         if (has_cpuflag(X86_FEATURE_RDRAND)) {
  62                 debug_putstr(" RDRAND");
  63                 if (rdrand_long(&raw)) {
  64                         random ^= raw;
  65                         use_i8254 = false;
  66                 }
  67         }
  68
  69         if (has_cpuflag(X86_FEATURE_TSC)) {
  70                 debug_putstr(" RDTSC");
  71                 raw = rdtsc();
  72
  73                 random ^= raw;
  74                 use_i8254 = false;
  75         }
  76
  77         if (use_i8254) {
  78                 debug_putstr(" i8254");
  79                 random ^= i8254();
  80         }
  81
  82         /* Circular multiply for better bit diffusion */
  83         asm(_ASM_MUL "%3"
  84             : "=a" (random), "=d" (raw)
  85             : "a" (random), "rm" (mix_const));
  86         random += raw;
  87
  88         debug_putstr("...\n");
  89
  90         return random;
  91 }