arch/s390/kernel/nospec-branch.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/module.h>
   3 #include <asm/nospec-branch.h>
   4
   5 int nospec_call_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF);
   6 int nospec_return_disable = !IS_ENABLED(CONFIG_EXPOLINE_FULL);
   7
   8 static int __init nospectre_v2_setup_early(char *str)
   9 {
  10         nospec_call_disable = 1;
  11         nospec_return_disable = 1;
  12         return 0;
  13 }
  14 early_param("nospectre_v2", nospectre_v2_setup_early);
  15
  16 static int __init spectre_v2_setup_early(char *str)
  17 {
  18         if (str && !strncmp(str, "on", 2)) {
  19                 nospec_call_disable = 0;
  20                 nospec_return_disable = 0;
  21         }
  22         if (str && !strncmp(str, "off", 3)) {
  23                 nospec_call_disable = 1;
  24                 nospec_return_disable = 1;
  25         }
  26         if (str && !strncmp(str, "auto", 4)) {
  27                 nospec_call_disable = 0;
  28                 nospec_return_disable = 1;
  29         }
  30         return 0;
  31 }
  32 early_param("spectre_v2", spectre_v2_setup_early);
  33
  34 static void __init_or_module __nospec_revert(s32 *start, s32 *end)
  35 {
  36         enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type;
  37         u8 *instr, *thunk, *br;
  38         u8 insnbuf[6];
  39         s32 *epo;
  40
  41         /* Second part of the instruction replace is always a nop */
  42         memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x00, 0x00 }, 4);
  43         for (epo = start; epo < end; epo++) {
  44                 instr = (u8 *) epo + *epo;
  45                 if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04)
  46                         type = BRCL_EXPOLINE;   /* brcl instruction */
  47                 else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05)
  48                         type = BRASL_EXPOLINE;  /* brasl instruction */
  49                 else
  50                         continue;
  51                 thunk = instr + (*(int *)(instr + 2)) * 2;
  52                 if (thunk[0] == 0xc6 && thunk[1] == 0x00)
  53                         /* exrl %r0,<target-br> */
  54                         br = thunk + (*(int *)(thunk + 2)) * 2;
  55                 else if (thunk[0] == 0xc0 && (thunk[1] & 0x0f) == 0x00 &&
  56                          thunk[6] == 0x44 && thunk[7] == 0x00 &&
  57                          (thunk[8] & 0x0f) == 0x00 && thunk[9] == 0x00 &&
  58                          (thunk[1] & 0xf0) == (thunk[8] & 0xf0))
  59                         /* larl %rx,<target br> + ex %r0,0(%rx) */
  60                         br = thunk + (*(int *)(thunk + 2)) * 2;
  61                 else
  62                         continue;
  63                 if (br[0] != 0x07 || (br[1] & 0xf0) != 0xf0)
  64                         continue;
  65                 switch (type) {
  66                 case BRCL_EXPOLINE:
  67                         /* brcl to thunk, replace with br + nop */
  68                         insnbuf[0] = br[0];
  69                         insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
  70                         break;
  71                 case BRASL_EXPOLINE:
  72                         /* brasl to thunk, replace with basr + nop */
  73                         insnbuf[0] = 0x0d;
  74                         insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
  75                         break;
  76                 }
  77
  78                 s390_kernel_write(instr, insnbuf, 6);
  79         }
  80 }
  81
  82 void __init_or_module nospec_call_revert(s32 *start, s32 *end)
  83 {
  84         if (nospec_call_disable)
  85                 __nospec_revert(start, end);
  86 }
  87
  88 void __init_or_module nospec_return_revert(s32 *start, s32 *end)
  89 {
  90         if (nospec_return_disable)
  91                 __nospec_revert(start, end);
  92 }
  93
  94 extern s32 __nospec_call_start[], __nospec_call_end[];
  95 extern s32 __nospec_return_start[], __nospec_return_end[];
  96 void __init nospec_init_branches(void)
  97 {
  98         nospec_call_revert(__nospec_call_start, __nospec_call_end);
  99         nospec_return_revert(__nospec_return_start, __nospec_return_end);
 100 }