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176 lines
4.7 KiB
176 lines
4.7 KiB
// 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, S390_lowcore.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, S390_lowcore.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, S390_lowcore.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 (__is_defined(CC_USING_EXPOLINE) && !nospec_disable) |
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pr_info("Spectre V2 mitigation: execute trampolines\n"); |
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if (__test_facility(82, S390_lowcore.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, S390_lowcore.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, S390_lowcore.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, S390_lowcore.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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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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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 if (thunk[0] == 0xc0 && (thunk[1] & 0x0f) == 0x00 && |
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thunk[6] == 0x44 && thunk[7] == 0x00 && |
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(thunk[8] & 0x0f) == 0x00 && thunk[9] == 0x00 && |
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(thunk[1] & 0xf0) == (thunk[8] & 0xf0)) |
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/* larl %rx,<target br> + ex %r0,0(%rx) */ |
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br = thunk + (*(int *)(thunk + 2)) * 2; |
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else |
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continue; |
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/* Check for unconditional branch 0x07f? or 0x47f???? */ |
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if ((br[0] & 0xbf) != 0x07 || (br[1] & 0xf0) != 0xf0) |
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continue; |
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memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x07, 0x00 }, 4); |
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switch (type) { |
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case BRCL_EXPOLINE: |
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insnbuf[0] = br[0]; |
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insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f); |
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if (br[0] == 0x47) { |
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/* brcl to b, replace with bc + nopr */ |
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insnbuf[2] = br[2]; |
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insnbuf[3] = br[3]; |
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} else { |
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/* brcl to br, replace with bcr + nop */ |
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} |
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break; |
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case BRASL_EXPOLINE: |
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insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f); |
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if (br[0] == 0x47) { |
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/* brasl to b, replace with bas + nopr */ |
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insnbuf[0] = 0x4d; |
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insnbuf[2] = br[2]; |
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insnbuf[3] = br[3]; |
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} else { |
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/* brasl to br, replace with basr + nop */ |
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insnbuf[0] = 0x0d; |
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} |
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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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