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![Vasily Gorbik](/assets/img/avatar_default.png)
Machine generations up to z9 (released in May 2006) have been officially out of service for several years now (z9 end of service - January 31, 2019). No distributions build kernels supporting those old machine generations anymore, except Debian, which seems to pick the oldest supported generation. The team supporting Debian on s390 has been notified about the change. Raising minimum supported machine generation to z10 helps to reduce maintenance cost and effectively remove code, which is not getting enough testing coverage due to lack of older hardware and distributions support. Besides that this unblocks some optimization opportunities and allows to use wider instruction set in asm files for future features implementation. Due to this change spectre mitigation and usercopy implementations could be drastically simplified and many newer instructions could be converted from ".insn" encoding to instruction names. Acked-by: Ilya Leoshkevich <iii@linux.ibm.com> Reviewed-by: Heiko Carstens <hca@linux.ibm.com> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
156 lines
4 KiB
C
156 lines
4 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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