// 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 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 "%s: " fmt "\n", __func__, ##args); \ } while (0) #define DUMP_BYTES(buf, len, fmt, args...) \ do { \ if (unlikely(debug_alternative)) { \ int j; \ \ if (!(len)) \ break; \ \ printk(KERN_DEBUG fmt, ##args); \ for (j = 0; j < (len) - 1; j++) \ printk(KERN_CONT "%02hhx ", buf[j]); \ printk(KERN_CONT "%02hhx\n", buf[j]); \ } \ } while (0) /* * Each GENERIC_NOPX is of X bytes, and defined as an array of bytes * that correspond to that nop. Getting from one nop to the next, we * add to the array the offset that is equal to the sum of all sizes of * nops preceding the one we are after. * * Note: The GENERIC_NOP5_ATOMIC is at the end, as it breaks the * nice symmetry of sizes of the previous nops. */ #if defined(GENERIC_NOP1) && !defined(CONFIG_X86_64) static const unsigned char intelnops[] = { GENERIC_NOP1, GENERIC_NOP2, GENERIC_NOP3, GENERIC_NOP4, GENERIC_NOP5, GENERIC_NOP6, GENERIC_NOP7, GENERIC_NOP8, GENERIC_NOP5_ATOMIC }; static const unsigned char * const intel_nops[ASM_NOP_MAX+2] = { NULL, intelnops, intelnops + 1, intelnops + 1 + 2, intelnops + 1 + 2 + 3, intelnops + 1 + 2 + 3 + 4, intelnops + 1 + 2 + 3 + 4 + 5, intelnops + 1 + 2 + 3 + 4 + 5 + 6, intelnops + 1 + 2 + 3 + 4 + 5 + 6 + 7, intelnops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8, }; #endif #ifdef K8_NOP1 static const unsigned char k8nops[] = { K8_NOP1, K8_NOP2, K8_NOP3, K8_NOP4, K8_NOP5, K8_NOP6, K8_NOP7, K8_NOP8, K8_NOP5_ATOMIC }; static const unsigned char * const k8_nops[ASM_NOP_MAX+2] = { NULL, k8nops, k8nops + 1, k8nops + 1 + 2, k8nops + 1 + 2 + 3, k8nops + 1 + 2 + 3 + 4, k8nops + 1 + 2 + 3 + 4 + 5, k8nops + 1 + 2 + 3 + 4 + 5 + 6, k8nops + 1 + 2 + 3 + 4 + 5 + 6 + 7, k8nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8, }; #endif #if defined(K7_NOP1) && !defined(CONFIG_X86_64) static const unsigned char k7nops[] = { K7_NOP1, K7_NOP2, K7_NOP3, K7_NOP4, K7_NOP5, K7_NOP6, K7_NOP7, K7_NOP8, K7_NOP5_ATOMIC }; static const unsigned char * const k7_nops[ASM_NOP_MAX+2] = { NULL, k7nops, k7nops + 1, k7nops + 1 + 2, k7nops + 1 + 2 + 3, k7nops + 1 + 2 + 3 + 4, k7nops + 1 + 2 + 3 + 4 + 5, k7nops + 1 + 2 + 3 + 4 + 5 + 6, k7nops + 1 + 2 + 3 + 4 + 5 + 6 + 7, k7nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8, }; #endif #ifdef P6_NOP1 static const unsigned char p6nops[] = { P6_NOP1, P6_NOP2, P6_NOP3, P6_NOP4, P6_NOP5, P6_NOP6, P6_NOP7, P6_NOP8, P6_NOP5_ATOMIC }; static const unsigned char * const p6_nops[ASM_NOP_MAX+2] = { NULL, p6nops, p6nops + 1, p6nops + 1 + 2, p6nops + 1 + 2 + 3, p6nops + 1 + 2 + 3 + 4, p6nops + 1 + 2 + 3 + 4 + 5, p6nops + 1 + 2 + 3 + 4 + 5 + 6, p6nops + 1 + 2 + 3 + 4 + 5 + 6 + 7, p6nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8, }; #endif /* Initialize these to a safe default */ #ifdef CONFIG_X86_64 const unsigned char * const *ideal_nops = p6_nops; #else const unsigned char * const *ideal_nops = intel_nops; #endif void __init arch_init_ideal_nops(void) { switch (boot_cpu_data.x86_vendor) { case X86_VENDOR_INTEL: /* * Due to a decoder implementation quirk, some * specific Intel CPUs actually perform better with * the "k8_nops" than with the SDM-recommended NOPs. */ if (boot_cpu_data.x86 == 6 && boot_cpu_data.x86_model >= 0x0f && boot_cpu_data.x86_model != 0x1c && boot_cpu_data.x86_model != 0x26 && boot_cpu_data.x86_model != 0x27 && boot_cpu_data.x86_model < 0x30) { ideal_nops = k8_nops; } else if (boot_cpu_has(X86_FEATURE_NOPL)) { ideal_nops = p6_nops; } else { #ifdef CONFIG_X86_64 ideal_nops = k8_nops; #else ideal_nops = intel_nops; #endif } break; case X86_VENDOR_HYGON: ideal_nops = p6_nops; return; case X86_VENDOR_AMD: if (boot_cpu_data.x86 > 0xf) { ideal_nops = p6_nops; return; } /* fall through */ default: #ifdef CONFIG_X86_64 ideal_nops = k8_nops; #else if (boot_cpu_has(X86_FEATURE_K8)) ideal_nops = k8_nops; else if (boot_cpu_has(X86_FEATURE_K7)) ideal_nops = k7_nops; else ideal_nops = intel_nops; #endif } } /* 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, ideal_nops[noplen], noplen); insns += noplen; len -= noplen; } } 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 *insnbuf) { u8 *next_rip, *tgt_rip; s32 n_dspl, o_dspl; int repl_len; if (a->replacementlen != 5) return; o_dspl = *(s32 *)(insnbuf + 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; insnbuf[0] = 0xeb; insnbuf[1] = (s8)n_dspl; add_nops(insnbuf + 2, 3); repl_len = 2; goto done; five_byte_jmp: n_dspl -= 5; insnbuf[0] = 0xe9; *(s32 *)&insnbuf[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); } /* * "noinline" to cause control flow change and thus invalidate I$ and * cause refetch after modification. */ static void __init_or_module noinline optimize_nops(struct alt_instr *a, u8 *instr) { unsigned long flags; int i; for (i = 0; i < a->padlen; i++) { if (instr[i] != 0x90) return; } local_irq_save(flags); add_nops(instr + (a->instrlen - a->padlen), a->padlen); local_irq_restore(flags); DUMP_BYTES(instr, a->instrlen, "%px: [%d:%d) optimized NOPs: ", instr, a->instrlen - a->padlen, a->padlen); } /* * 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 insnbuf[MAX_PATCH_LEN]; DPRINTK("alt table %px, -> %px", start, end); /* * 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 insnbuf_sz = 0; instr = (u8 *)&a->instr_offset + a->instr_offset; replacement = (u8 *)&a->repl_offset + a->repl_offset; BUG_ON(a->instrlen > sizeof(insnbuf)); BUG_ON(a->cpuid >= (NCAPINTS + NBUGINTS) * 32); if (!boot_cpu_has(a->cpuid)) { if (a->padlen > 1) optimize_nops(a, instr); continue; } DPRINTK("feat: %d*32+%d, old: (%pS (%px) len: %d), repl: (%px, len: %d), pad: %d", a->cpuid >> 5, a->cpuid & 0x1f, instr, instr, a->instrlen, replacement, a->replacementlen, a->padlen); DUMP_BYTES(instr, a->instrlen, "%px: old_insn: ", instr); DUMP_BYTES(replacement, a->replacementlen, "%px: rpl_insn: ", replacement); memcpy(insnbuf, replacement, a->replacementlen); insnbuf_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 && *insnbuf == 0xe8) { *(s32 *)(insnbuf + 1) += replacement - instr; DPRINTK("Fix CALL offset: 0x%x, CALL 0x%lx", *(s32 *)(insnbuf + 1), (unsigned long)instr + *(s32 *)(insnbuf + 1) + 5); } if (a->replacementlen && is_jmp(replacement[0])) recompute_jump(a, instr, replacement, insnbuf); if (a->instrlen > a->replacementlen) { add_nops(insnbuf + a->replacementlen, a->instrlen - a->replacementlen); insnbuf_sz += a->instrlen - a->replacementlen; } DUMP_BYTES(insnbuf, insnbuf_sz, "%px: final_insn: ", instr); text_poke_early(instr, insnbuf, insnbuf_sz); } } #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 insnbuf[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(insnbuf, p->instr, p->len); used = pv_ops.init.patch(p->instrtype, insnbuf, (unsigned long)p->instr, p->len); BUG_ON(used > p->len); /* Pad the rest with nops */ add_nops(insnbuf + used, p->len - used); text_poke_early(p->instr, insnbuf, 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. */ static void __init int3_magic(unsigned int *ptr) { *ptr = 1; } 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_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 a 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. */ 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 apply_paravirt(__parainstructions, __parainstructions_end); 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 again 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); local_irq_restore(flags); sync_core(); /* * Could also do a CLFLUSH here to speed up CPU recovery; but * that causes hangs on some VIA CPUs. */ } } __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])); local_irq_save(flags); /* * 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); 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)); pte_unmap_unlock(ptep, ptl); local_irq_restore(flags); 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(); } static bool bp_patching_in_progress; static void *bp_int3_handler, *bp_int3_addr; int poke_int3_handler(struct pt_regs *regs) { /* * Having observed our INT3 instruction, we now must observe * bp_patching_in_progress. * * in_progress = TRUE INT3 * WMB RMB * write INT3 if (in_progress) * * Idem for bp_int3_handler. */ smp_rmb(); if (likely(!bp_patching_in_progress)) return 0; if (user_mode(regs) || regs->ip != (unsigned long)bp_int3_addr) return 0; /* set up the specified breakpoint handler */ regs->ip = (unsigned long) bp_int3_handler; return 1; } NOKPROBE_SYMBOL(poke_int3_handler); /** * text_poke_bp() -- update instructions on live kernel on SMP * @addr: address to patch * @opcode: opcode of new instruction * @len: length to copy * @handler: address to jump to when the temporary breakpoint is hit * * 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: * - add a int3 trap to the address that will be patched * - sync cores * - update all but the first byte of the patched range * - sync cores * - replace the first byte (int3) by the first byte of * replacing opcode * - sync cores */ void text_poke_bp(void *addr, const void *opcode, size_t len, void *handler) { unsigned char int3 = 0xcc; bp_int3_handler = handler; bp_int3_addr = (u8 *)addr + sizeof(int3); bp_patching_in_progress = true; lockdep_assert_held(&text_mutex); /* * Corresponding read barrier in int3 notifier for making sure the * in_progress and handler are correctly ordered wrt. patching. */ smp_wmb(); text_poke(addr, &int3, sizeof(int3)); on_each_cpu(do_sync_core, NULL, 1); if (len - sizeof(int3) > 0) { /* patch all but the first byte */ text_poke((char *)addr + sizeof(int3), (const char *) opcode + sizeof(int3), len - sizeof(int3)); /* * 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). */ on_each_cpu(do_sync_core, NULL, 1); } /* patch the first byte */ text_poke(addr, opcode, sizeof(int3)); on_each_cpu(do_sync_core, NULL, 1); /* * sync_core() implies an smp_mb() and orders this store against * the writing of the new instruction. */ bp_patching_in_progress = false; }