arch/riscv/include/asm/archrandom.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * Kernel interface for the RISCV arch_random_* functions
   4  *
   5  * Copyright (c) 2023 Rivos Inc.
   6  *
   7  */
   8
   9 #ifndef ASM_RISCV_ARCHRANDOM_H
  10 #define ASM_RISCV_ARCHRANDOM_H
  11
  12 #include <asm/csr.h>
  13 #include <asm/processor.h>
  14
  15 #define SEED_RETRY_LOOPS 100
  16
  17 static inline bool __must_check csr_seed_long(unsigned long *v)
  18 {
  19         unsigned int retry = SEED_RETRY_LOOPS, valid_seeds = 0;
  20         const int needed_seeds = sizeof(long) / sizeof(u16);
  21         u16 *entropy = (u16 *)v;
  22
  23         do {
  24                 /*
  25                  * The SEED CSR must be accessed with a read-write instruction.
  26                  */
  27                 unsigned long csr_seed = csr_swap(CSR_SEED, 0);
  28                 unsigned long opst = csr_seed & SEED_OPST_MASK;
  29
  30                 switch (opst) {
  31                 case SEED_OPST_ES16:
  32                         entropy[valid_seeds++] = csr_seed & SEED_ENTROPY_MASK;
  33                         if (valid_seeds == needed_seeds)
  34                                 return true;
  35                         break;
  36
  37                 case SEED_OPST_DEAD:
  38                         pr_err_once("archrandom: Unrecoverable error\n");
  39                         return false;
  40
  41                 case SEED_OPST_BIST:
  42                 case SEED_OPST_WAIT:
  43                 default:
  44                         cpu_relax();
  45                         continue;
  46                 }
  47         } while (--retry);
  48
  49         return false;
  50 }
  51
  52 static inline size_t __must_check arch_get_random_longs(unsigned long *v, size_t max_longs)
  53 {
  54         return 0;
  55 }
  56
  57 static inline size_t __must_check arch_get_random_seed_longs(unsigned long *v, size_t max_longs)
  58 {
  59         if (!max_longs)
  60                 return 0;
  61
  62         /*
  63          * If Zkr is supported and csr_seed_long succeeds, we return one long
  64          * worth of entropy.
  65          */
  66         if (riscv_has_extension_likely(RISCV_ISA_EXT_ZKR) && csr_seed_long(v))
  67                 return 1;
  68
  69         return 0;
  70 }
  71
  72 #endif /* ASM_RISCV_ARCHRANDOM_H */