157 lines
4.0 KiB
C
157 lines
4.0 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/module.h>
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#include <linux/device.h>
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#include <linux/cpu.h>
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#include <asm/nospec-branch.h>
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static int __init nobp_setup_early(char *str)
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{
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bool enabled;
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int rc;
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rc = kstrtobool(str, &enabled);
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if (rc)
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return rc;
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if (enabled && test_facility(82)) {
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/*
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* The user explicitely requested nobp=1, enable it and
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* disable the expoline support.
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*/
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__set_facility(82, alt_stfle_fac_list);
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if (IS_ENABLED(CONFIG_EXPOLINE))
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nospec_disable = 1;
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} else {
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__clear_facility(82, alt_stfle_fac_list);
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}
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return 0;
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}
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early_param("nobp", nobp_setup_early);
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static int __init nospec_setup_early(char *str)
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{
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__clear_facility(82, alt_stfle_fac_list);
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return 0;
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}
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early_param("nospec", nospec_setup_early);
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static int __init nospec_report(void)
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{
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if (test_facility(156))
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pr_info("Spectre V2 mitigation: etokens\n");
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if (nospec_uses_trampoline())
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pr_info("Spectre V2 mitigation: execute trampolines\n");
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if (__test_facility(82, alt_stfle_fac_list))
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pr_info("Spectre V2 mitigation: limited branch prediction\n");
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return 0;
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}
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arch_initcall(nospec_report);
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#ifdef CONFIG_EXPOLINE
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int nospec_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF);
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static int __init nospectre_v2_setup_early(char *str)
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{
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nospec_disable = 1;
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return 0;
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}
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early_param("nospectre_v2", nospectre_v2_setup_early);
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void __init nospec_auto_detect(void)
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{
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if (test_facility(156) || cpu_mitigations_off()) {
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/*
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* The machine supports etokens.
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* Disable expolines and disable nobp.
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*/
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if (__is_defined(CC_USING_EXPOLINE))
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nospec_disable = 1;
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__clear_facility(82, alt_stfle_fac_list);
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} else if (__is_defined(CC_USING_EXPOLINE)) {
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/*
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* The kernel has been compiled with expolines.
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* Keep expolines enabled and disable nobp.
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*/
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nospec_disable = 0;
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__clear_facility(82, alt_stfle_fac_list);
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}
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/*
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* If the kernel has not been compiled with expolines the
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* nobp setting decides what is done, this depends on the
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* CONFIG_KERNEL_NP option and the nobp/nospec parameters.
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*/
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}
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static int __init spectre_v2_setup_early(char *str)
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{
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if (str && !strncmp(str, "on", 2)) {
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nospec_disable = 0;
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__clear_facility(82, alt_stfle_fac_list);
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}
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if (str && !strncmp(str, "off", 3))
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nospec_disable = 1;
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if (str && !strncmp(str, "auto", 4))
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nospec_auto_detect();
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return 0;
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}
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early_param("spectre_v2", spectre_v2_setup_early);
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static void __init_or_module __nospec_revert(s32 *start, s32 *end)
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{
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enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type;
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static const u8 branch[] = { 0x47, 0x00, 0x07, 0x00 };
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u8 *instr, *thunk, *br;
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u8 insnbuf[6];
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s32 *epo;
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/* Second part of the instruction replace is always a nop */
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memcpy(insnbuf + 2, branch, sizeof(branch));
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for (epo = start; epo < end; epo++) {
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instr = (u8 *) epo + *epo;
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if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04)
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type = BRCL_EXPOLINE; /* brcl instruction */
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else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05)
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type = BRASL_EXPOLINE; /* brasl instruction */
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else
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continue;
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thunk = instr + (*(int *)(instr + 2)) * 2;
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if (thunk[0] == 0xc6 && thunk[1] == 0x00)
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/* exrl %r0,<target-br> */
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br = thunk + (*(int *)(thunk + 2)) * 2;
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else
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continue;
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if (br[0] != 0x07 || (br[1] & 0xf0) != 0xf0)
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continue;
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switch (type) {
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case BRCL_EXPOLINE:
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/* brcl to thunk, replace with br + nop */
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insnbuf[0] = br[0];
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insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
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break;
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case BRASL_EXPOLINE:
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/* brasl to thunk, replace with basr + nop */
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insnbuf[0] = 0x0d;
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insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
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break;
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}
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s390_kernel_write(instr, insnbuf, 6);
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}
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}
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void __init_or_module nospec_revert(s32 *start, s32 *end)
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{
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if (nospec_disable)
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__nospec_revert(start, end);
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}
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extern s32 __nospec_call_start[], __nospec_call_end[];
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extern s32 __nospec_return_start[], __nospec_return_end[];
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void __init nospec_init_branches(void)
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{
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nospec_revert(__nospec_call_start, __nospec_call_end);
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nospec_revert(__nospec_return_start, __nospec_return_end);
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}
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#endif /* CONFIG_EXPOLINE */
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