// SPDX-License-Identifier: GPL-2.0-only #define pr_fmt(fmt) "SMP alternatives: " fmt #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include int __read_mostly alternatives_patched; EXPORT_SYMBOL_GPL(alternatives_patched); #define MAX_PATCH_LEN (255-1) static int __initdata_or_module debug_alternative; static int __init debug_alt(char *str) { debug_alternative = 1; return 1; } __setup("debug-alternative", debug_alt); static int noreplace_smp; static int __init setup_noreplace_smp(char *str) { noreplace_smp = 1; return 1; } __setup("noreplace-smp", setup_noreplace_smp); #define DPRINTK(fmt, args...) \ do { \ if (debug_alternative) \ printk(KERN_DEBUG pr_fmt(fmt) "\n", ##args); \ } while (0) #define DUMP_BYTES(buf, len, fmt, args...) \ do { \ if (unlikely(debug_alternative)) { \ int j; \ \ if (!(len)) \ break; \ \ printk(KERN_DEBUG pr_fmt(fmt), ##args); \ for (j = 0; j < (len) - 1; j++) \ printk(KERN_CONT "%02hhx ", buf[j]); \ printk(KERN_CONT "%02hhx\n", buf[j]); \ } \ } while (0) static const unsigned char x86nops[] = { BYTES_NOP1, BYTES_NOP2, BYTES_NOP3, BYTES_NOP4, BYTES_NOP5, BYTES_NOP6, BYTES_NOP7, BYTES_NOP8, }; const unsigned char * const x86_nops[ASM_NOP_MAX+1] = { NULL, x86nops, x86nops + 1, x86nops + 1 + 2, x86nops + 1 + 2 + 3, x86nops + 1 + 2 + 3 + 4, x86nops + 1 + 2 + 3 + 4 + 5, x86nops + 1 + 2 + 3 + 4 + 5 + 6, x86nops + 1 + 2 + 3 + 4 + 5 + 6 + 7, }; /* Use this to add nops to a buffer, then text_poke the whole buffer. */ static void __init_or_module add_nops(void *insns, unsigned int len) { while (len > 0) { unsigned int noplen = len; if (noplen > ASM_NOP_MAX) noplen = ASM_NOP_MAX; memcpy(insns, x86_nops[noplen], noplen); insns += noplen; len -= noplen; } } extern s32 __retpoline_sites[], __retpoline_sites_end[]; extern s32 __return_sites[], __return_sites_end[]; extern struct alt_instr __alt_instructions[], __alt_instructions_end[]; extern s32 __smp_locks[], __smp_locks_end[]; void text_poke_early(void *addr, const void *opcode, size_t len); /* * Are we looking at a near JMP with a 1 or 4-byte displacement. */ static inline bool is_jmp(const u8 opcode) { return opcode == 0xeb || opcode == 0xe9; } static void __init_or_module recompute_jump(struct alt_instr *a, u8 *orig_insn, u8 *repl_insn, u8 *insn_buff) { u8 *next_rip, *tgt_rip; s32 n_dspl, o_dspl; int repl_len; if (a->replacementlen != 5) return; o_dspl = *(s32 *)(insn_buff + 1); /* next_rip of the replacement JMP */ next_rip = repl_insn + a->replacementlen; /* target rip of the replacement JMP */ tgt_rip = next_rip + o_dspl; n_dspl = tgt_rip - orig_insn; DPRINTK("target RIP: %px, new_displ: 0x%x", tgt_rip, n_dspl); if (tgt_rip - orig_insn >= 0) { if (n_dspl - 2 <= 127) goto two_byte_jmp; else goto five_byte_jmp; /* negative offset */ } else { if (((n_dspl - 2) & 0xff) == (n_dspl - 2)) goto two_byte_jmp; else goto five_byte_jmp; } two_byte_jmp: n_dspl -= 2; insn_buff[0] = 0xeb; insn_buff[1] = (s8)n_dspl; add_nops(insn_buff + 2, 3); repl_len = 2; goto done; five_byte_jmp: n_dspl -= 5; insn_buff[0] = 0xe9; *(s32 *)&insn_buff[1] = n_dspl; repl_len = 5; done: DPRINTK("final displ: 0x%08x, JMP 0x%lx", n_dspl, (unsigned long)orig_insn + n_dspl + repl_len); } /* * optimize_nops_range() - Optimize a sequence of single byte NOPs (0x90) * * @instr: instruction byte stream * @instrlen: length of the above * @off: offset within @instr where the first NOP has been detected * * Return: number of NOPs found (and replaced). */ static __always_inline int optimize_nops_range(u8 *instr, u8 instrlen, int off) { unsigned long flags; int i = off, nnops; while (i < instrlen) { if (instr[i] != 0x90) break; i++; } nnops = i - off; if (nnops <= 1) return nnops; local_irq_save(flags); add_nops(instr + off, nnops); local_irq_restore(flags); DUMP_BYTES(instr, instrlen, "%px: [%d:%d) optimized NOPs: ", instr, off, i); return nnops; } /* * "noinline" to cause control flow change and thus invalidate I$ and * cause refetch after modification. */ static void __init_or_module noinline optimize_nops(u8 *instr, size_t len) { struct insn insn; int i = 0; /* * Jump over the non-NOP insns and optimize single-byte NOPs into bigger * ones. */ for (;;) { if (insn_decode_kernel(&insn, &instr[i])) return; /* * See if this and any potentially following NOPs can be * optimized. */ if (insn.length == 1 && insn.opcode.bytes[0] == 0x90) i += optimize_nops_range(instr, len, i); else i += insn.length; if (i >= len) return; } } /* * Replace instructions with better alternatives for this CPU type. This runs * before SMP is initialized to avoid SMP problems with self modifying code. * This implies that asymmetric systems where APs have less capabilities than * the boot processor are not handled. Tough. Make sure you disable such * features by hand. * * Marked "noinline" to cause control flow change and thus insn cache * to refetch changed I$ lines. */ void __init_or_module noinline apply_alternatives(struct alt_instr *start, struct alt_instr *end) { struct alt_instr *a; u8 *instr, *replacement; u8 insn_buff[MAX_PATCH_LEN]; DPRINTK("alt table %px, -> %px", start, end); /* * In the case CONFIG_X86_5LEVEL=y, KASAN_SHADOW_START is defined using * cpu_feature_enabled(X86_FEATURE_LA57) and is therefore patched here. * During the process, KASAN becomes confused seeing partial LA57 * conversion and triggers a false-positive out-of-bound report. * * Disable KASAN until the patching is complete. */ kasan_disable_current(); /* * The scan order should be from start to end. A later scanned * alternative code can overwrite previously scanned alternative code. * Some kernel functions (e.g. memcpy, memset, etc) use this order to * patch code. * * So be careful if you want to change the scan order to any other * order. */ for (a = start; a < end; a++) { int insn_buff_sz = 0; /* Mask away "NOT" flag bit for feature to test. */ u16 feature = a->cpuid & ~ALTINSTR_FLAG_INV; instr = (u8 *)&a->instr_offset + a->instr_offset; replacement = (u8 *)&a->repl_offset + a->repl_offset; BUG_ON(a->instrlen > sizeof(insn_buff)); BUG_ON(feature >= (NCAPINTS + NBUGINTS) * 32); /* * Patch if either: * - feature is present * - feature not present but ALTINSTR_FLAG_INV is set to mean, * patch if feature is *NOT* present. */ if (!boot_cpu_has(feature) == !(a->cpuid & ALTINSTR_FLAG_INV)) goto next; DPRINTK("feat: %s%d*32+%d, old: (%pS (%px) len: %d), repl: (%px, len: %d)", (a->cpuid & ALTINSTR_FLAG_INV) ? "!" : "", feature >> 5, feature & 0x1f, instr, instr, a->instrlen, replacement, a->replacementlen); DUMP_BYTES(instr, a->instrlen, "%px: old_insn: ", instr); DUMP_BYTES(replacement, a->replacementlen, "%px: rpl_insn: ", replacement); memcpy(insn_buff, replacement, a->replacementlen); insn_buff_sz = a->replacementlen; /* * 0xe8 is a relative jump; fix the offset. * * Instruction length is checked before the opcode to avoid * accessing uninitialized bytes for zero-length replacements. */ if (a->replacementlen == 5 && *insn_buff == 0xe8) { *(s32 *)(insn_buff + 1) += replacement - instr; DPRINTK("Fix CALL offset: 0x%x, CALL 0x%lx", *(s32 *)(insn_buff + 1), (unsigned long)instr + *(s32 *)(insn_buff + 1) + 5); } if (a->replacementlen && is_jmp(replacement[0])) recompute_jump(a, instr, replacement, insn_buff); for (; insn_buff_sz < a->instrlen; insn_buff_sz++) insn_buff[insn_buff_sz] = 0x90; DUMP_BYTES(insn_buff, insn_buff_sz, "%px: final_insn: ", instr); text_poke_early(instr, insn_buff, insn_buff_sz); next: optimize_nops(instr, a->instrlen); } kasan_enable_current(); } #if defined(CONFIG_RETPOLINE) && defined(CONFIG_STACK_VALIDATION) /* * CALL/JMP *%\reg */ static int emit_indirect(int op, int reg, u8 *bytes) { int i = 0; u8 modrm; switch (op) { case CALL_INSN_OPCODE: modrm = 0x10; /* Reg = 2; CALL r/m */ break; case JMP32_INSN_OPCODE: modrm = 0x20; /* Reg = 4; JMP r/m */ break; default: WARN_ON_ONCE(1); return -1; } if (reg >= 8) { bytes[i++] = 0x41; /* REX.B prefix */ reg -= 8; } modrm |= 0xc0; /* Mod = 3 */ modrm += reg; bytes[i++] = 0xff; /* opcode */ bytes[i++] = modrm; return i; } /* * Rewrite the compiler generated retpoline thunk calls. * * For spectre_v2=off (!X86_FEATURE_RETPOLINE), rewrite them into immediate * indirect instructions, avoiding the extra indirection. * * For example, convert: * * CALL __x86_indirect_thunk_\reg * * into: * * CALL *%\reg * * It also tries to inline spectre_v2=retpoline,amd when size permits. */ static int patch_retpoline(void *addr, struct insn *insn, u8 *bytes) { retpoline_thunk_t *target; int reg, ret, i = 0; u8 op, cc; target = addr + insn->length + insn->immediate.value; reg = target - __x86_indirect_thunk_array; if (WARN_ON_ONCE(reg & ~0xf)) return -1; /* If anyone ever does: CALL/JMP *%rsp, we're in deep trouble. */ BUG_ON(reg == 4); if (cpu_feature_enabled(X86_FEATURE_RETPOLINE) && !cpu_feature_enabled(X86_FEATURE_RETPOLINE_LFENCE)) return -1; op = insn->opcode.bytes[0]; /* * Convert: * * Jcc.d32 __x86_indirect_thunk_\reg * * into: * * Jncc.d8 1f * [ LFENCE ] * JMP *%\reg * [ NOP ] * 1: */ /* Jcc.d32 second opcode byte is in the range: 0x80-0x8f */ if (op == 0x0f && (insn->opcode.bytes[1] & 0xf0) == 0x80) { cc = insn->opcode.bytes[1] & 0xf; cc ^= 1; /* invert condition */ bytes[i++] = 0x70 + cc; /* Jcc.d8 */ bytes[i++] = insn->length - 2; /* sizeof(Jcc.d8) == 2 */ /* Continue as if: JMP.d32 __x86_indirect_thunk_\reg */ op = JMP32_INSN_OPCODE; } /* * For RETPOLINE_AMD: prepend the indirect CALL/JMP with an LFENCE. */ if (cpu_feature_enabled(X86_FEATURE_RETPOLINE_LFENCE)) { bytes[i++] = 0x0f; bytes[i++] = 0xae; bytes[i++] = 0xe8; /* LFENCE */ } ret = emit_indirect(op, reg, bytes + i); if (ret < 0) return ret; i += ret; for (; i < insn->length;) bytes[i++] = BYTES_NOP1; return i; } /* * Generated by 'objtool --retpoline'. */ void __init_or_module noinline apply_retpolines(s32 *start, s32 *end) { s32 *s; for (s = start; s < end; s++) { void *addr = (void *)s + *s; struct insn insn; int len, ret; u8 bytes[16]; u8 op1, op2; ret = insn_decode_kernel(&insn, addr); if (WARN_ON_ONCE(ret < 0)) continue; op1 = insn.opcode.bytes[0]; op2 = insn.opcode.bytes[1]; switch (op1) { case CALL_INSN_OPCODE: case JMP32_INSN_OPCODE: break; case 0x0f: /* escape */ if (op2 >= 0x80 && op2 <= 0x8f) break; fallthrough; default: WARN_ON_ONCE(1); continue; } DPRINTK("retpoline at: %pS (%px) len: %d to: %pS", addr, addr, insn.length, addr + insn.length + insn.immediate.value); len = patch_retpoline(addr, &insn, bytes); if (len == insn.length) { optimize_nops(bytes, len); DUMP_BYTES(((u8*)addr), len, "%px: orig: ", addr); DUMP_BYTES(((u8*)bytes), len, "%px: repl: ", addr); text_poke_early(addr, bytes, len); } } } #ifdef CONFIG_RETHUNK /* * Rewrite the compiler generated return thunk tail-calls. * * For example, convert: * * JMP __x86_return_thunk * * into: * * RET */ static int patch_return(void *addr, struct insn *insn, u8 *bytes) { int i = 0; if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) { if (x86_return_thunk == __x86_return_thunk) return -1; i = JMP32_INSN_SIZE; __text_gen_insn(bytes, JMP32_INSN_OPCODE, addr, x86_return_thunk, i); } else { bytes[i++] = RET_INSN_OPCODE; } for (; i < insn->length;) bytes[i++] = INT3_INSN_OPCODE; return i; } void __init_or_module noinline apply_returns(s32 *start, s32 *end) { s32 *s; for (s = start; s < end; s++) { void *dest = NULL, *addr = (void *)s + *s; struct insn insn; int len, ret; u8 bytes[16]; u8 op; ret = insn_decode_kernel(&insn, addr); if (WARN_ON_ONCE(ret < 0)) continue; op = insn.opcode.bytes[0]; if (op == JMP32_INSN_OPCODE) dest = addr + insn.length + insn.immediate.value; if (__static_call_fixup(addr, op, dest) || WARN_ONCE(dest != &__x86_return_thunk, "missing return thunk: %pS-%pS: %*ph", addr, dest, 5, addr)) continue; DPRINTK("return thunk at: %pS (%px) len: %d to: %pS", addr, addr, insn.length, addr + insn.length + insn.immediate.value); len = patch_return(addr, &insn, bytes); if (len == insn.length) { DUMP_BYTES(((u8*)addr), len, "%px: orig: ", addr); DUMP_BYTES(((u8*)bytes), len, "%px: repl: ", addr); text_poke_early(addr, bytes, len); } } } #else void __init_or_module noinline apply_returns(s32 *start, s32 *end) { } #endif /* CONFIG_RETHUNK */ #else /* !RETPOLINES || !CONFIG_STACK_VALIDATION */ void __init_or_module noinline apply_retpolines(s32 *start, s32 *end) { } void __init_or_module noinline apply_returns(s32 *start, s32 *end) { } #endif /* CONFIG_RETPOLINE && CONFIG_STACK_VALIDATION */ #ifdef CONFIG_SMP static void alternatives_smp_lock(const s32 *start, const s32 *end, u8 *text, u8 *text_end) { const s32 *poff; for (poff = start; poff < end; poff++) { u8 *ptr = (u8 *)poff + *poff; if (!*poff || ptr < text || ptr >= text_end) continue; /* turn DS segment override prefix into lock prefix */ if (*ptr == 0x3e) text_poke(ptr, ((unsigned char []){0xf0}), 1); } } static void alternatives_smp_unlock(const s32 *start, const s32 *end, u8 *text, u8 *text_end) { const s32 *poff; for (poff = start; poff < end; poff++) { u8 *ptr = (u8 *)poff + *poff; if (!*poff || ptr < text || ptr >= text_end) continue; /* turn lock prefix into DS segment override prefix */ if (*ptr == 0xf0) text_poke(ptr, ((unsigned char []){0x3E}), 1); } } struct smp_alt_module { /* what is this ??? */ struct module *mod; char *name; /* ptrs to lock prefixes */ const s32 *locks; const s32 *locks_end; /* .text segment, needed to avoid patching init code ;) */ u8 *text; u8 *text_end; struct list_head next; }; static LIST_HEAD(smp_alt_modules); static bool uniproc_patched = false; /* protected by text_mutex */ void __init_or_module alternatives_smp_module_add(struct module *mod, char *name, void *locks, void *locks_end, void *text, void *text_end) { struct smp_alt_module *smp; mutex_lock(&text_mutex); if (!uniproc_patched) goto unlock; if (num_possible_cpus() == 1) /* Don't bother remembering, we'll never have to undo it. */ goto smp_unlock; smp = kzalloc(sizeof(*smp), GFP_KERNEL); if (NULL == smp) /* we'll run the (safe but slow) SMP code then ... */ goto unlock; smp->mod = mod; smp->name = name; smp->locks = locks; smp->locks_end = locks_end; smp->text = text; smp->text_end = text_end; DPRINTK("locks %p -> %p, text %p -> %p, name %s\n", smp->locks, smp->locks_end, smp->text, smp->text_end, smp->name); list_add_tail(&smp->next, &smp_alt_modules); smp_unlock: alternatives_smp_unlock(locks, locks_end, text, text_end); unlock: mutex_unlock(&text_mutex); } void __init_or_module alternatives_smp_module_del(struct module *mod) { struct smp_alt_module *item; mutex_lock(&text_mutex); list_for_each_entry(item, &smp_alt_modules, next) { if (mod != item->mod) continue; list_del(&item->next); kfree(item); break; } mutex_unlock(&text_mutex); } void alternatives_enable_smp(void) { struct smp_alt_module *mod; /* Why bother if there are no other CPUs? */ BUG_ON(num_possible_cpus() == 1); mutex_lock(&text_mutex); if (uniproc_patched) { pr_info("switching to SMP code\n"); BUG_ON(num_online_cpus() != 1); clear_cpu_cap(&boot_cpu_data, X86_FEATURE_UP); clear_cpu_cap(&cpu_data(0), X86_FEATURE_UP); list_for_each_entry(mod, &smp_alt_modules, next) alternatives_smp_lock(mod->locks, mod->locks_end, mod->text, mod->text_end); uniproc_patched = false; } mutex_unlock(&text_mutex); } /* * Return 1 if the address range is reserved for SMP-alternatives. * Must hold text_mutex. */ int alternatives_text_reserved(void *start, void *end) { struct smp_alt_module *mod; const s32 *poff; u8 *text_start = start; u8 *text_end = end; lockdep_assert_held(&text_mutex); list_for_each_entry(mod, &smp_alt_modules, next) { if (mod->text > text_end || mod->text_end < text_start) continue; for (poff = mod->locks; poff < mod->locks_end; poff++) { const u8 *ptr = (const u8 *)poff + *poff; if (text_start <= ptr && text_end > ptr) return 1; } } return 0; } #endif /* CONFIG_SMP */ #ifdef CONFIG_PARAVIRT void __init_or_module apply_paravirt(struct paravirt_patch_site *start, struct paravirt_patch_site *end) { struct paravirt_patch_site *p; char insn_buff[MAX_PATCH_LEN]; for (p = start; p < end; p++) { unsigned int used; BUG_ON(p->len > MAX_PATCH_LEN); /* prep the buffer with the original instructions */ memcpy(insn_buff, p->instr, p->len); used = paravirt_patch(p->type, insn_buff, (unsigned long)p->instr, p->len); BUG_ON(used > p->len); /* Pad the rest with nops */ add_nops(insn_buff + used, p->len - used); text_poke_early(p->instr, insn_buff, p->len); } } extern struct paravirt_patch_site __start_parainstructions[], __stop_parainstructions[]; #endif /* CONFIG_PARAVIRT */ /* * Self-test for the INT3 based CALL emulation code. * * This exercises int3_emulate_call() to make sure INT3 pt_regs are set up * properly and that there is a stack gap between the INT3 frame and the * previous context. Without this gap doing a virtual PUSH on the interrupted * stack would corrupt the INT3 IRET frame. * * See entry_{32,64}.S for more details. */ /* * We define the int3_magic() function in assembly to control the calling * convention such that we can 'call' it from assembly. */ extern void int3_magic(unsigned int *ptr); /* defined in asm */ asm ( " .pushsection .init.text, \"ax\", @progbits\n" " .type int3_magic, @function\n" "int3_magic:\n" " movl $1, (%" _ASM_ARG1 ")\n" ASM_RET " .size int3_magic, .-int3_magic\n" " .popsection\n" ); extern __initdata unsigned long int3_selftest_ip; /* defined in asm below */ static int __init int3_exception_notify(struct notifier_block *self, unsigned long val, void *data) { struct die_args *args = data; struct pt_regs *regs = args->regs; if (!regs || user_mode(regs)) return NOTIFY_DONE; if (val != DIE_INT3) return NOTIFY_DONE; if (regs->ip - INT3_INSN_SIZE != int3_selftest_ip) return NOTIFY_DONE; int3_emulate_call(regs, (unsigned long)&int3_magic); return NOTIFY_STOP; } static void __init int3_selftest(void) { static __initdata struct notifier_block int3_exception_nb = { .notifier_call = int3_exception_notify, .priority = INT_MAX-1, /* last */ }; unsigned int val = 0; BUG_ON(register_die_notifier(&int3_exception_nb)); /* * Basically: int3_magic(&val); but really complicated :-) * * Stick the address of the INT3 instruction into int3_selftest_ip, * then trigger the INT3, padded with NOPs to match a CALL instruction * length. */ asm volatile ("1: int3; nop; nop; nop; nop\n\t" ".pushsection .init.data,\"aw\"\n\t" ".align " __ASM_SEL(4, 8) "\n\t" ".type int3_selftest_ip, @object\n\t" ".size int3_selftest_ip, " __ASM_SEL(4, 8) "\n\t" "int3_selftest_ip:\n\t" __ASM_SEL(.long, .quad) " 1b\n\t" ".popsection\n\t" : ASM_CALL_CONSTRAINT : __ASM_SEL_RAW(a, D) (&val) : "memory"); BUG_ON(val != 1); unregister_die_notifier(&int3_exception_nb); } void __init alternative_instructions(void) { int3_selftest(); /* * The patching is not fully atomic, so try to avoid local * interruptions that might execute the to be patched code. * Other CPUs are not running. */ stop_nmi(); /* * Don't stop machine check exceptions while patching. * MCEs only happen when something got corrupted and in this * case we must do something about the corruption. * Ignoring it is worse than an unlikely patching race. * Also machine checks tend to be broadcast and if one CPU * goes into machine check the others follow quickly, so we don't * expect a machine check to cause undue problems during to code * patching. */ /* * Paravirt patching and alternative patching can be combined to * replace a function call with a short direct code sequence (e.g. * by setting a constant return value instead of doing that in an * external function). * In order to make this work the following sequence is required: * 1. set (artificial) features depending on used paravirt * functions which can later influence alternative patching * 2. apply paravirt patching (generally replacing an indirect * function call with a direct one) * 3. apply alternative patching (e.g. replacing a direct function * call with a custom code sequence) * Doing paravirt patching after alternative patching would clobber * the optimization of the custom code with a function call again. */ paravirt_set_cap(); /* * First patch paravirt functions, such that we overwrite the indirect * call with the direct call. */ apply_paravirt(__parainstructions, __parainstructions_end); /* * Rewrite the retpolines, must be done before alternatives since * those can rewrite the retpoline thunks. */ apply_retpolines(__retpoline_sites, __retpoline_sites_end); apply_returns(__return_sites, __return_sites_end); /* * Then patch alternatives, such that those paravirt calls that are in * alternatives can be overwritten by their immediate fragments. */ apply_alternatives(__alt_instructions, __alt_instructions_end); #ifdef CONFIG_SMP /* Patch to UP if other cpus not imminent. */ if (!noreplace_smp && (num_present_cpus() == 1 || setup_max_cpus <= 1)) { uniproc_patched = true; alternatives_smp_module_add(NULL, "core kernel", __smp_locks, __smp_locks_end, _text, _etext); } if (!uniproc_patched || num_possible_cpus() == 1) { free_init_pages("SMP alternatives", (unsigned long)__smp_locks, (unsigned long)__smp_locks_end); } #endif restart_nmi(); alternatives_patched = 1; } /** * text_poke_early - Update instructions on a live kernel at boot time * @addr: address to modify * @opcode: source of the copy * @len: length to copy * * When you use this code to patch more than one byte of an instruction * you need to make sure that other CPUs cannot execute this code in parallel. * Also no thread must be currently preempted in the middle of these * instructions. And on the local CPU you need to be protected against NMI or * MCE handlers seeing an inconsistent instruction while you patch. */ void __init_or_module text_poke_early(void *addr, const void *opcode, size_t len) { unsigned long flags; if (boot_cpu_has(X86_FEATURE_NX) && is_module_text_address((unsigned long)addr)) { /* * Modules text is marked initially as non-executable, so the * code cannot be running and speculative code-fetches are * prevented. Just change the code. */ memcpy(addr, opcode, len); } else { local_irq_save(flags); memcpy(addr, opcode, len); sync_core(); local_irq_restore(flags); /* * Could also do a CLFLUSH here to speed up CPU recovery; but * that causes hangs on some VIA CPUs. */ } } typedef struct { struct mm_struct *mm; } temp_mm_state_t; /* * Using a temporary mm allows to set temporary mappings that are not accessible * by other CPUs. Such mappings are needed to perform sensitive memory writes * that override the kernel memory protections (e.g., W^X), without exposing the * temporary page-table mappings that are required for these write operations to * other CPUs. Using a temporary mm also allows to avoid TLB shootdowns when the * mapping is torn down. * * Context: The temporary mm needs to be used exclusively by a single core. To * harden security IRQs must be disabled while the temporary mm is * loaded, thereby preventing interrupt handler bugs from overriding * the kernel memory protection. */ static inline temp_mm_state_t use_temporary_mm(struct mm_struct *mm) { temp_mm_state_t temp_state; lockdep_assert_irqs_disabled(); /* * Make sure not to be in TLB lazy mode, as otherwise we'll end up * with a stale address space WITHOUT being in lazy mode after * restoring the previous mm. */ if (this_cpu_read(cpu_tlbstate_shared.is_lazy)) leave_mm(smp_processor_id()); temp_state.mm = this_cpu_read(cpu_tlbstate.loaded_mm); switch_mm_irqs_off(NULL, mm, current); /* * If breakpoints are enabled, disable them while the temporary mm is * used. Userspace might set up watchpoints on addresses that are used * in the temporary mm, which would lead to wrong signals being sent or * crashes. * * Note that breakpoints are not disabled selectively, which also causes * kernel breakpoints (e.g., perf's) to be disabled. This might be * undesirable, but still seems reasonable as the code that runs in the * temporary mm should be short. */ if (hw_breakpoint_active()) hw_breakpoint_disable(); return temp_state; } static inline void unuse_temporary_mm(temp_mm_state_t prev_state) { lockdep_assert_irqs_disabled(); switch_mm_irqs_off(NULL, prev_state.mm, current); /* * Restore the breakpoints if they were disabled before the temporary mm * was loaded. */ if (hw_breakpoint_active()) hw_breakpoint_restore(); } __ro_after_init struct mm_struct *poking_mm; __ro_after_init unsigned long poking_addr; static void *__text_poke(void *addr, const void *opcode, size_t len) { bool cross_page_boundary = offset_in_page(addr) + len > PAGE_SIZE; struct page *pages[2] = {NULL}; temp_mm_state_t prev; unsigned long flags; pte_t pte, *ptep; spinlock_t *ptl; pgprot_t pgprot; /* * While boot memory allocator is running we cannot use struct pages as * they are not yet initialized. There is no way to recover. */ BUG_ON(!after_bootmem); if (!core_kernel_text((unsigned long)addr)) { pages[0] = vmalloc_to_page(addr); if (cross_page_boundary) pages[1] = vmalloc_to_page(addr + PAGE_SIZE); } else { pages[0] = virt_to_page(addr); WARN_ON(!PageReserved(pages[0])); if (cross_page_boundary) pages[1] = virt_to_page(addr + PAGE_SIZE); } /* * If something went wrong, crash and burn since recovery paths are not * implemented. */ BUG_ON(!pages[0] || (cross_page_boundary && !pages[1])); /* * Map the page without the global bit, as TLB flushing is done with * flush_tlb_mm_range(), which is intended for non-global PTEs. */ pgprot = __pgprot(pgprot_val(PAGE_KERNEL) & ~_PAGE_GLOBAL); /* * The lock is not really needed, but this allows to avoid open-coding. */ ptep = get_locked_pte(poking_mm, poking_addr, &ptl); /* * This must not fail; preallocated in poking_init(). */ VM_BUG_ON(!ptep); local_irq_save(flags); pte = mk_pte(pages[0], pgprot); set_pte_at(poking_mm, poking_addr, ptep, pte); if (cross_page_boundary) { pte = mk_pte(pages[1], pgprot); set_pte_at(poking_mm, poking_addr + PAGE_SIZE, ptep + 1, pte); } /* * Loading the temporary mm behaves as a compiler barrier, which * guarantees that the PTE will be set at the time memcpy() is done. */ prev = use_temporary_mm(poking_mm); kasan_disable_current(); memcpy((u8 *)poking_addr + offset_in_page(addr), opcode, len); kasan_enable_current(); /* * Ensure that the PTE is only cleared after the instructions of memcpy * were issued by using a compiler barrier. */ barrier(); pte_clear(poking_mm, poking_addr, ptep); if (cross_page_boundary) pte_clear(poking_mm, poking_addr + PAGE_SIZE, ptep + 1); /* * Loading the previous page-table hierarchy requires a serializing * instruction that already allows the core to see the updated version. * Xen-PV is assumed to serialize execution in a similar manner. */ unuse_temporary_mm(prev); /* * Flushing the TLB might involve IPIs, which would require enabled * IRQs, but not if the mm is not used, as it is in this point. */ flush_tlb_mm_range(poking_mm, poking_addr, poking_addr + (cross_page_boundary ? 2 : 1) * PAGE_SIZE, PAGE_SHIFT, false); /* * If the text does not match what we just wrote then something is * fundamentally screwy; there's nothing we can really do about that. */ BUG_ON(memcmp(addr, opcode, len)); local_irq_restore(flags); pte_unmap_unlock(ptep, ptl); return addr; } /** * text_poke - Update instructions on a live kernel * @addr: address to modify * @opcode: source of the copy * @len: length to copy * * Only atomic text poke/set should be allowed when not doing early patching. * It means the size must be writable atomically and the address must be aligned * in a way that permits an atomic write. It also makes sure we fit on a single * page. * * Note that the caller must ensure that if the modified code is part of a * module, the module would not be removed during poking. This can be achieved * by registering a module notifier, and ordering module removal and patching * trough a mutex. */ void *text_poke(void *addr, const void *opcode, size_t len) { lockdep_assert_held(&text_mutex); return __text_poke(addr, opcode, len); } /** * text_poke_kgdb - Update instructions on a live kernel by kgdb * @addr: address to modify * @opcode: source of the copy * @len: length to copy * * Only atomic text poke/set should be allowed when not doing early patching. * It means the size must be writable atomically and the address must be aligned * in a way that permits an atomic write. It also makes sure we fit on a single * page. * * Context: should only be used by kgdb, which ensures no other core is running, * despite the fact it does not hold the text_mutex. */ void *text_poke_kgdb(void *addr, const void *opcode, size_t len) { return __text_poke(addr, opcode, len); } static void do_sync_core(void *info) { sync_core(); } void text_poke_sync(void) { on_each_cpu(do_sync_core, NULL, 1); } struct text_poke_loc { /* addr := _stext + rel_addr */ s32 rel_addr; s32 disp; u8 len; u8 opcode; const u8 text[POKE_MAX_OPCODE_SIZE]; /* see text_poke_bp_batch() */ u8 old; }; struct bp_patching_desc { struct text_poke_loc *vec; int nr_entries; atomic_t refs; }; static struct bp_patching_desc bp_desc; static __always_inline struct bp_patching_desc *try_get_desc(void) { struct bp_patching_desc *desc = &bp_desc; if (!arch_atomic_inc_not_zero(&desc->refs)) return NULL; return desc; } static __always_inline void put_desc(void) { struct bp_patching_desc *desc = &bp_desc; smp_mb__before_atomic(); arch_atomic_dec(&desc->refs); } static __always_inline void *text_poke_addr(struct text_poke_loc *tp) { return _stext + tp->rel_addr; } static __always_inline int patch_cmp(const void *key, const void *elt) { struct text_poke_loc *tp = (struct text_poke_loc *) elt; if (key < text_poke_addr(tp)) return -1; if (key > text_poke_addr(tp)) return 1; return 0; } noinstr int poke_int3_handler(struct pt_regs *regs) { struct bp_patching_desc *desc; struct text_poke_loc *tp; int ret = 0; void *ip; if (user_mode(regs)) return 0; /* * Having observed our INT3 instruction, we now must observe * bp_desc with non-zero refcount: * * bp_desc.refs = 1 INT3 * WMB RMB * write INT3 if (bp_desc.refs != 0) */ smp_rmb(); desc = try_get_desc(); if (!desc) return 0; /* * Discount the INT3. See text_poke_bp_batch(). */ ip = (void *) regs->ip - INT3_INSN_SIZE; /* * Skip the binary search if there is a single member in the vector. */ if (unlikely(desc->nr_entries > 1)) { tp = __inline_bsearch(ip, desc->vec, desc->nr_entries, sizeof(struct text_poke_loc), patch_cmp); if (!tp) goto out_put; } else { tp = desc->vec; if (text_poke_addr(tp) != ip) goto out_put; } ip += tp->len; switch (tp->opcode) { case INT3_INSN_OPCODE: /* * Someone poked an explicit INT3, they'll want to handle it, * do not consume. */ goto out_put; case RET_INSN_OPCODE: int3_emulate_ret(regs); break; case CALL_INSN_OPCODE: int3_emulate_call(regs, (long)ip + tp->disp); break; case JMP32_INSN_OPCODE: case JMP8_INSN_OPCODE: int3_emulate_jmp(regs, (long)ip + tp->disp); break; default: BUG(); } ret = 1; out_put: put_desc(); return ret; } #define TP_VEC_MAX (PAGE_SIZE / sizeof(struct text_poke_loc)) static struct text_poke_loc tp_vec[TP_VEC_MAX]; static int tp_vec_nr; /** * text_poke_bp_batch() -- update instructions on live kernel on SMP * @tp: vector of instructions to patch * @nr_entries: number of entries in the vector * * Modify multi-byte instruction by using int3 breakpoint on SMP. * We completely avoid stop_machine() here, and achieve the * synchronization using int3 breakpoint. * * The way it is done: * - For each entry in the vector: * - add a int3 trap to the address that will be patched * - sync cores * - For each entry in the vector: * - update all but the first byte of the patched range * - sync cores * - For each entry in the vector: * - replace the first byte (int3) by the first byte of * replacing opcode * - sync cores */ static void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries) { unsigned char int3 = INT3_INSN_OPCODE; unsigned int i; int do_sync; lockdep_assert_held(&text_mutex); bp_desc.vec = tp; bp_desc.nr_entries = nr_entries; /* * Corresponds to the implicit memory barrier in try_get_desc() to * ensure reading a non-zero refcount provides up to date bp_desc data. */ atomic_set_release(&bp_desc.refs, 1); /* * Corresponding read barrier in int3 notifier for making sure the * nr_entries and handler are correctly ordered wrt. patching. */ smp_wmb(); /* * First step: add a int3 trap to the address that will be patched. */ for (i = 0; i < nr_entries; i++) { tp[i].old = *(u8 *)text_poke_addr(&tp[i]); text_poke(text_poke_addr(&tp[i]), &int3, INT3_INSN_SIZE); } text_poke_sync(); /* * Second step: update all but the first byte of the patched range. */ for (do_sync = 0, i = 0; i < nr_entries; i++) { u8 old[POKE_MAX_OPCODE_SIZE] = { tp[i].old, }; int len = tp[i].len; if (len - INT3_INSN_SIZE > 0) { memcpy(old + INT3_INSN_SIZE, text_poke_addr(&tp[i]) + INT3_INSN_SIZE, len - INT3_INSN_SIZE); text_poke(text_poke_addr(&tp[i]) + INT3_INSN_SIZE, (const char *)tp[i].text + INT3_INSN_SIZE, len - INT3_INSN_SIZE); do_sync++; } /* * Emit a perf event to record the text poke, primarily to * support Intel PT decoding which must walk the executable code * to reconstruct the trace. The flow up to here is: * - write INT3 byte * - IPI-SYNC * - write instruction tail * At this point the actual control flow will be through the * INT3 and handler and not hit the old or new instruction. * Intel PT outputs FUP/TIP packets for the INT3, so the flow * can still be decoded. Subsequently: * - emit RECORD_TEXT_POKE with the new instruction * - IPI-SYNC * - write first byte * - IPI-SYNC * So before the text poke event timestamp, the decoder will see * either the old instruction flow or FUP/TIP of INT3. After the * text poke event timestamp, the decoder will see either the * new instruction flow or FUP/TIP of INT3. Thus decoders can * use the timestamp as the point at which to modify the * executable code. * The old instruction is recorded so that the event can be * processed forwards or backwards. */ perf_event_text_poke(text_poke_addr(&tp[i]), old, len, tp[i].text, len); } if (do_sync) { /* * According to Intel, this core syncing is very likely * not necessary and we'd be safe even without it. But * better safe than sorry (plus there's not only Intel). */ text_poke_sync(); } /* * Third step: replace the first byte (int3) by the first byte of * replacing opcode. */ for (do_sync = 0, i = 0; i < nr_entries; i++) { if (tp[i].text[0] == INT3_INSN_OPCODE) continue; text_poke(text_poke_addr(&tp[i]), tp[i].text, INT3_INSN_SIZE); do_sync++; } if (do_sync) text_poke_sync(); /* * Remove and wait for refs to be zero. */ if (!atomic_dec_and_test(&bp_desc.refs)) atomic_cond_read_acquire(&bp_desc.refs, !VAL); } static void text_poke_loc_init(struct text_poke_loc *tp, void *addr, const void *opcode, size_t len, const void *emulate) { struct insn insn; int ret, i; memcpy((void *)tp->text, opcode, len); if (!emulate) emulate = opcode; ret = insn_decode_kernel(&insn, emulate); BUG_ON(ret < 0); tp->rel_addr = addr - (void *)_stext; tp->len = len; tp->opcode = insn.opcode.bytes[0]; switch (tp->opcode) { case RET_INSN_OPCODE: case JMP32_INSN_OPCODE: case JMP8_INSN_OPCODE: /* * Control flow instructions without implied execution of the * next instruction can be padded with INT3. */ for (i = insn.length; i < len; i++) BUG_ON(tp->text[i] != INT3_INSN_OPCODE); break; default: BUG_ON(len != insn.length); }; switch (tp->opcode) { case INT3_INSN_OPCODE: case RET_INSN_OPCODE: break; case CALL_INSN_OPCODE: case JMP32_INSN_OPCODE: case JMP8_INSN_OPCODE: tp->disp = insn.immediate.value; break; default: /* assume NOP */ switch (len) { case 2: /* NOP2 -- emulate as JMP8+0 */ BUG_ON(memcmp(emulate, x86_nops[len], len)); tp->opcode = JMP8_INSN_OPCODE; tp->disp = 0; break; case 5: /* NOP5 -- emulate as JMP32+0 */ BUG_ON(memcmp(emulate, x86_nops[len], len)); tp->opcode = JMP32_INSN_OPCODE; tp->disp = 0; break; default: /* unknown instruction */ BUG(); } break; } } /* * We hard rely on the tp_vec being ordered; ensure this is so by flushing * early if needed. */ static bool tp_order_fail(void *addr) { struct text_poke_loc *tp; if (!tp_vec_nr) return false; if (!addr) /* force */ return true; tp = &tp_vec[tp_vec_nr - 1]; if ((unsigned long)text_poke_addr(tp) > (unsigned long)addr) return true; return false; } static void text_poke_flush(void *addr) { if (tp_vec_nr == TP_VEC_MAX || tp_order_fail(addr)) { text_poke_bp_batch(tp_vec, tp_vec_nr); tp_vec_nr = 0; } } void text_poke_finish(void) { text_poke_flush(NULL); } void __ref text_poke_queue(void *addr, const void *opcode, size_t len, const void *emulate) { struct text_poke_loc *tp; if (unlikely(system_state == SYSTEM_BOOTING)) { text_poke_early(addr, opcode, len); return; } text_poke_flush(addr); tp = &tp_vec[tp_vec_nr++]; text_poke_loc_init(tp, addr, opcode, len, emulate); } /** * text_poke_bp() -- update instructions on live kernel on SMP * @addr: address to patch * @opcode: opcode of new instruction * @len: length to copy * @emulate: instruction to be emulated * * Update a single instruction with the vector in the stack, avoiding * dynamically allocated memory. This function should be used when it is * not possible to allocate memory. */ void __ref text_poke_bp(void *addr, const void *opcode, size_t len, const void *emulate) { struct text_poke_loc tp; if (unlikely(system_state == SYSTEM_BOOTING)) { text_poke_early(addr, opcode, len); return; } text_poke_loc_init(&tp, addr, opcode, len, emulate); text_poke_bp_batch(&tp, 1); }