// SPDX-License-Identifier: GPL-2.0
  #include <linux/module.h>

  #include <linux/device.h>

  #include <linux/cpu.h>

  #include <asm/nospec-branch.h>

  static int __init nobp_setup_early(char *str)
  {
  	bool enabled;
  	int rc;
  
  	rc = kstrtobool(str, &enabled);
  	if (rc)
  		return rc;

  	if (enabled && test_facility(82)) {
  		/*
  		 * The user explicitely requested nobp=1, enable it and
  		 * disable the expoline support.
  		 */

  		__set_facility(82, S390_lowcore.alt_stfle_fac_list);

  		if (IS_ENABLED(CONFIG_EXPOLINE))
  			nospec_disable = 1;
  	} else {

  		__clear_facility(82, S390_lowcore.alt_stfle_fac_list);

  	}

  	return 0;
  }
  early_param("nobp", nobp_setup_early);
  
  static int __init nospec_setup_early(char *str)
  {
  	__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
  	return 0;
  }
  early_param("nospec", nospec_setup_early);

  static int __init nospec_report(void)
  {

  	if (test_facility(156))
  		pr_info("Spectre V2 mitigation: etokens
  ");

  	if (__is_defined(CC_USING_EXPOLINE) && !nospec_disable)

  		pr_info("Spectre V2 mitigation: execute trampolines
  ");

  	if (__test_facility(82, S390_lowcore.alt_stfle_fac_list))

  		pr_info("Spectre V2 mitigation: limited branch prediction
  ");

  	return 0;
  }
  arch_initcall(nospec_report);

  #ifdef CONFIG_EXPOLINE

  int nospec_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF);

  
  static int __init nospectre_v2_setup_early(char *str)
  {

  	nospec_disable = 1;

  	return 0;
  }
  early_param("nospectre_v2", nospectre_v2_setup_early);

  void __init nospec_auto_detect(void)

  {

  	if (test_facility(156) || cpu_mitigations_off()) {

  		/*
  		 * The machine supports etokens.
  		 * Disable expolines and disable nobp.
  		 */

  		if (__is_defined(CC_USING_EXPOLINE))

  			nospec_disable = 1;
  		__clear_facility(82, S390_lowcore.alt_stfle_fac_list);

  	} else if (__is_defined(CC_USING_EXPOLINE)) {

  		/*
  		 * The kernel has been compiled with expolines.
  		 * Keep expolines enabled and disable nobp.
  		 */
  		nospec_disable = 0;
  		__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
  	}
  	/*
  	 * If the kernel has not been compiled with expolines the
  	 * nobp setting decides what is done, this depends on the
  	 * CONFIG_KERNEL_NP option and the nobp/nospec parameters.
  	 */

  }

  static int __init spectre_v2_setup_early(char *str)
  {
  	if (str && !strncmp(str, "on", 2)) {

  		nospec_disable = 0;
  		__clear_facility(82, S390_lowcore.alt_stfle_fac_list);

  	}

  	if (str && !strncmp(str, "off", 3))
  		nospec_disable = 1;
  	if (str && !strncmp(str, "auto", 4))

  		nospec_auto_detect();

  	return 0;
  }
  early_param("spectre_v2", spectre_v2_setup_early);
  
  static void __init_or_module __nospec_revert(s32 *start, s32 *end)
  {
  	enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type;
  	u8 *instr, *thunk, *br;
  	u8 insnbuf[6];
  	s32 *epo;
  
  	/* Second part of the instruction replace is always a nop */

  	for (epo = start; epo < end; epo++) {
  		instr = (u8 *) epo + *epo;
  		if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04)
  			type = BRCL_EXPOLINE;	/* brcl instruction */
  		else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05)
  			type = BRASL_EXPOLINE;	/* brasl instruction */
  		else
  			continue;
  		thunk = instr + (*(int *)(instr + 2)) * 2;
  		if (thunk[0] == 0xc6 && thunk[1] == 0x00)
  			/* exrl %r0,<target-br> */
  			br = thunk + (*(int *)(thunk + 2)) * 2;
  		else if (thunk[0] == 0xc0 && (thunk[1] & 0x0f) == 0x00 &&
  			 thunk[6] == 0x44 && thunk[7] == 0x00 &&
  			 (thunk[8] & 0x0f) == 0x00 && thunk[9] == 0x00 &&
  			 (thunk[1] & 0xf0) == (thunk[8] & 0xf0))
  			/* larl %rx,<target br> + ex %r0,0(%rx) */
  			br = thunk + (*(int *)(thunk + 2)) * 2;
  		else
  			continue;

  		/* Check for unconditional branch 0x07f? or 0x47f???? */
  		if ((br[0] & 0xbf) != 0x07 || (br[1] & 0xf0) != 0xf0)

  			continue;

  
  		memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x07, 0x00 }, 4);

  		switch (type) {
  		case BRCL_EXPOLINE:

  			insnbuf[0] = br[0];
  			insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);

  			if (br[0] == 0x47) {
  				/* brcl to b, replace with bc + nopr */
  				insnbuf[2] = br[2];
  				insnbuf[3] = br[3];
  			} else {
  				/* brcl to br, replace with bcr + nop */
  			}

  			break;
  		case BRASL_EXPOLINE:

  			insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);

  			if (br[0] == 0x47) {
  				/* brasl to b, replace with bas + nopr */
  				insnbuf[0] = 0x4d;
  				insnbuf[2] = br[2];
  				insnbuf[3] = br[3];
  			} else {
  				/* brasl to br, replace with basr + nop */
  				insnbuf[0] = 0x0d;
  			}

  			break;
  		}
  
  		s390_kernel_write(instr, insnbuf, 6);
  	}
  }

  void __init_or_module nospec_revert(s32 *start, s32 *end)

  {

  	if (nospec_disable)

  		__nospec_revert(start, end);
  }
  
  extern s32 __nospec_call_start[], __nospec_call_end[];
  extern s32 __nospec_return_start[], __nospec_return_end[];
  void __init nospec_init_branches(void)
  {

  	nospec_revert(__nospec_call_start, __nospec_call_end);
  	nospec_revert(__nospec_return_start, __nospec_return_end);

  }

  
  #endif /* CONFIG_EXPOLINE */