arch/s390/kernel/nospec-branch.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/module.h>
   3 #include <linux/device.h>
   4 #include <asm/facility.h>
   5 #include <asm/nospec-branch.h>
   6
   7 static int __init nobp_setup_early(char *str)
   8 {
   9         bool enabled;
  10         int rc;
  11
  12         rc = kstrtobool(str, &enabled);
  13         if (rc)
  14                 return rc;
  15         if (enabled && test_facility(82)) {
  16                 /*
  17                  * The user explicitely requested nobp=1, enable it and
  18                  * disable the expoline support.
  19                  */
  20                 __set_facility(82, S390_lowcore.alt_stfle_fac_list);
  21                 if (IS_ENABLED(CONFIG_EXPOLINE))
  22                         nospec_disable = 1;
  23         } else {
  24                 __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
  25         }
  26         return 0;
  27 }
  28 early_param("nobp", nobp_setup_early);
  29
  30 static int __init nospec_setup_early(char *str)
  31 {
  32         __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
  33         return 0;
  34 }
  35 early_param("nospec", nospec_setup_early);
  36
  37 static int __init nospec_report(void)
  38 {
  39         if (IS_ENABLED(CC_USING_EXPOLINE) && !nospec_disable)
  40                 pr_info("Spectre V2 mitigation: execute trampolines.\n");
  41         if (__test_facility(82, S390_lowcore.alt_stfle_fac_list))
  42                 pr_info("Spectre V2 mitigation: limited branch prediction.\n");
  43         return 0;
  44 }
  45 arch_initcall(nospec_report);
  46
  47 #ifdef CONFIG_EXPOLINE
  48
  49 int nospec_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF);
  50
  51 static int __init nospectre_v2_setup_early(char *str)
  52 {
  53         nospec_disable = 1;
  54         return 0;
  55 }
  56 early_param("nospectre_v2", nospectre_v2_setup_early);
  57
  58 void __init nospec_auto_detect(void)
  59 {
  60         if (IS_ENABLED(CC_USING_EXPOLINE)) {
  61                 /*
  62                  * The kernel has been compiled with expolines.
  63                  * Keep expolines enabled and disable nobp.
  64                  */
  65                 nospec_disable = 0;
  66                 __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
  67         }
  68         /*
  69          * If the kernel has not been compiled with expolines the
  70          * nobp setting decides what is done, this depends on the
  71          * CONFIG_KERNEL_NP option and the nobp/nospec parameters.
  72          */
  73 }
  74
  75 static int __init spectre_v2_setup_early(char *str)
  76 {
  77         if (str && !strncmp(str, "on", 2)) {
  78                 nospec_disable = 0;
  79                 __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
  80         }
  81         if (str && !strncmp(str, "off", 3))
  82                 nospec_disable = 1;
  83         if (str && !strncmp(str, "auto", 4))
  84                 nospec_auto_detect();
  85         return 0;
  86 }
  87 early_param("spectre_v2", spectre_v2_setup_early);
  88
  89 static void __init_or_module __nospec_revert(s32 *start, s32 *end)
  90 {
  91         enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type;
  92         u8 *instr, *thunk, *br;
  93         u8 insnbuf[6];
  94         s32 *epo;
  95
  96         /* Second part of the instruction replace is always a nop */
  97         for (epo = start; epo < end; epo++) {
  98                 instr = (u8 *) epo + *epo;
  99                 if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04)
 100                         type = BRCL_EXPOLINE;   /* brcl instruction */
 101                 else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05)
 102                         type = BRASL_EXPOLINE;  /* brasl instruction */
 103                 else
 104                         continue;
 105                 thunk = instr + (*(int *)(instr + 2)) * 2;
 106                 if (thunk[0] == 0xc6 && thunk[1] == 0x00)
 107                         /* exrl %r0,<target-br> */
 108                         br = thunk + (*(int *)(thunk + 2)) * 2;
 109                 else if (thunk[0] == 0xc0 && (thunk[1] & 0x0f) == 0x00 &&
 110                          thunk[6] == 0x44 && thunk[7] == 0x00 &&
 111                          (thunk[8] & 0x0f) == 0x00 && thunk[9] == 0x00 &&
 112                          (thunk[1] & 0xf0) == (thunk[8] & 0xf0))
 113                         /* larl %rx,<target br> + ex %r0,0(%rx) */
 114                         br = thunk + (*(int *)(thunk + 2)) * 2;
 115                 else
 116                         continue;
 117                 /* Check for unconditional branch 0x07f? or 0x47f???? */
 118                 if ((br[0] & 0xbf) != 0x07 || (br[1] & 0xf0) != 0xf0)
 119                         continue;
 120
 121                 memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x07, 0x00 }, 4);
 122                 switch (type) {
 123                 case BRCL_EXPOLINE:
 124                         insnbuf[0] = br[0];
 125                         insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
 126                         if (br[0] == 0x47) {
 127                                 /* brcl to b, replace with bc + nopr */
 128                                 insnbuf[2] = br[2];
 129                                 insnbuf[3] = br[3];
 130                         } else {
 131                                 /* brcl to br, replace with bcr + nop */
 132                         }
 133                         break;
 134                 case BRASL_EXPOLINE:
 135                         insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
 136                         if (br[0] == 0x47) {
 137                                 /* brasl to b, replace with bas + nopr */
 138                                 insnbuf[0] = 0x4d;
 139                                 insnbuf[2] = br[2];
 140                                 insnbuf[3] = br[3];
 141                         } else {
 142                                 /* brasl to br, replace with basr + nop */
 143                                 insnbuf[0] = 0x0d;
 144                         }
 145                         break;
 146                 }
 147
 148                 s390_kernel_write(instr, insnbuf, 6);
 149         }
 150 }
 151
 152 void __init_or_module nospec_revert(s32 *start, s32 *end)
 153 {
 154         if (nospec_disable)
 155                 __nospec_revert(start, end);
 156 }
 157
 158 extern s32 __nospec_call_start[], __nospec_call_end[];
 159 extern s32 __nospec_return_start[], __nospec_return_end[];
 160 void __init nospec_init_branches(void)
 161 {
 162         nospec_revert(__nospec_call_start, __nospec_call_end);
 163         nospec_revert(__nospec_return_start, __nospec_return_end);
 164 }
 165
 166 #endif /* CONFIG_EXPOLINE */