/* * Copyright (C) 1991, 1992 Linus Torvalds * Copyright (C) 2000, 2001, 2002 Andi Kleen, SuSE Labs * * Pentium III FXSR, SSE support * Gareth Hughes , May 2000 */ /* * Handle hardware traps and faults. */ #define pr_fmt(fmt) KBUILD_MODNAME ": " 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 #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 #ifdef CONFIG_X86_64 #include #else #include #include #endif #include DECLARE_BITMAP(system_vectors, NR_VECTORS); __always_inline int is_valid_bugaddr(unsigned long addr) { if (addr < TASK_SIZE_MAX) return 0; /* * We got #UD, if the text isn't readable we'd have gotten * a different exception. */ return *(unsigned short *)addr == INSN_UD2; } static nokprobe_inline int do_trap_no_signal(struct task_struct *tsk, int trapnr, const char *str, struct pt_regs *regs, long error_code) { if (v8086_mode(regs)) { /* * Traps 0, 1, 3, 4, and 5 should be forwarded to vm86. * On nmi (interrupt 2), do_trap should not be called. */ if (trapnr < X86_TRAP_UD) { if (!handle_vm86_trap((struct kernel_vm86_regs *) regs, error_code, trapnr)) return 0; } } else if (!user_mode(regs)) { if (fixup_exception(regs, trapnr, error_code, 0)) return 0; tsk->thread.error_code = error_code; tsk->thread.trap_nr = trapnr; die(str, regs, error_code); } else { if (fixup_vdso_exception(regs, trapnr, error_code, 0)) return 0; } /* * We want error_code and trap_nr set for userspace faults and * kernelspace faults which result in die(), but not * kernelspace faults which are fixed up. die() gives the * process no chance to handle the signal and notice the * kernel fault information, so that won't result in polluting * the information about previously queued, but not yet * delivered, faults. See also exc_general_protection below. */ tsk->thread.error_code = error_code; tsk->thread.trap_nr = trapnr; return -1; } static void show_signal(struct task_struct *tsk, int signr, const char *type, const char *desc, struct pt_regs *regs, long error_code) { if (show_unhandled_signals && unhandled_signal(tsk, signr) && printk_ratelimit()) { pr_info("%s[%d] %s%s ip:%lx sp:%lx error:%lx", tsk->comm, task_pid_nr(tsk), type, desc, regs->ip, regs->sp, error_code); print_vma_addr(KERN_CONT " in ", regs->ip); pr_cont("\n"); } } static void do_trap(int trapnr, int signr, char *str, struct pt_regs *regs, long error_code, int sicode, void __user *addr) { struct task_struct *tsk = current; if (!do_trap_no_signal(tsk, trapnr, str, regs, error_code)) return; show_signal(tsk, signr, "trap ", str, regs, error_code); if (!sicode) force_sig(signr); else force_sig_fault(signr, sicode, addr); } NOKPROBE_SYMBOL(do_trap); static void do_error_trap(struct pt_regs *regs, long error_code, char *str, unsigned long trapnr, int signr, int sicode, void __user *addr) { RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) != NOTIFY_STOP) { cond_local_irq_enable(regs); do_trap(trapnr, signr, str, regs, error_code, sicode, addr); cond_local_irq_disable(regs); } } /* * Posix requires to provide the address of the faulting instruction for * SIGILL (#UD) and SIGFPE (#DE) in the si_addr member of siginfo_t. * * This address is usually regs->ip, but when an uprobe moved the code out * of line then regs->ip points to the XOL code which would confuse * anything which analyzes the fault address vs. the unmodified binary. If * a trap happened in XOL code then uprobe maps regs->ip back to the * original instruction address. */ static __always_inline void __user *error_get_trap_addr(struct pt_regs *regs) { return (void __user *)uprobe_get_trap_addr(regs); } DEFINE_IDTENTRY(exc_divide_error) { do_error_trap(regs, 0, "divide error", X86_TRAP_DE, SIGFPE, FPE_INTDIV, error_get_trap_addr(regs)); } DEFINE_IDTENTRY(exc_overflow) { do_error_trap(regs, 0, "overflow", X86_TRAP_OF, SIGSEGV, 0, NULL); } #ifdef CONFIG_X86_F00F_BUG void handle_invalid_op(struct pt_regs *regs) #else static inline void handle_invalid_op(struct pt_regs *regs) #endif { do_error_trap(regs, 0, "invalid opcode", X86_TRAP_UD, SIGILL, ILL_ILLOPN, error_get_trap_addr(regs)); } static noinstr bool handle_bug(struct pt_regs *regs) { bool handled = false; /* * Normally @regs are unpoisoned by irqentry_enter(), but handle_bug() * is a rare case that uses @regs without passing them to * irqentry_enter(). */ kmsan_unpoison_entry_regs(regs); if (!is_valid_bugaddr(regs->ip)) return handled; /* * All lies, just get the WARN/BUG out. */ instrumentation_begin(); /* * Since we're emulating a CALL with exceptions, restore the interrupt * state to what it was at the exception site. */ if (regs->flags & X86_EFLAGS_IF) raw_local_irq_enable(); if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN || handle_cfi_failure(regs) == BUG_TRAP_TYPE_WARN) { regs->ip += LEN_UD2; handled = true; } if (regs->flags & X86_EFLAGS_IF) raw_local_irq_disable(); instrumentation_end(); return handled; } DEFINE_IDTENTRY_RAW(exc_invalid_op) { irqentry_state_t state; /* * We use UD2 as a short encoding for 'CALL __WARN', as such * handle it before exception entry to avoid recursive WARN * in case exception entry is the one triggering WARNs. */ if (!user_mode(regs) && handle_bug(regs)) return; state = irqentry_enter(regs); instrumentation_begin(); handle_invalid_op(regs); instrumentation_end(); irqentry_exit(regs, state); } DEFINE_IDTENTRY(exc_coproc_segment_overrun) { do_error_trap(regs, 0, "coprocessor segment overrun", X86_TRAP_OLD_MF, SIGFPE, 0, NULL); } DEFINE_IDTENTRY_ERRORCODE(exc_invalid_tss) { do_error_trap(regs, error_code, "invalid TSS", X86_TRAP_TS, SIGSEGV, 0, NULL); } DEFINE_IDTENTRY_ERRORCODE(exc_segment_not_present) { do_error_trap(regs, error_code, "segment not present", X86_TRAP_NP, SIGBUS, 0, NULL); } DEFINE_IDTENTRY_ERRORCODE(exc_stack_segment) { do_error_trap(regs, error_code, "stack segment", X86_TRAP_SS, SIGBUS, 0, NULL); } DEFINE_IDTENTRY_ERRORCODE(exc_alignment_check) { char *str = "alignment check"; if (notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_AC, SIGBUS) == NOTIFY_STOP) return; if (!user_mode(regs)) die("Split lock detected\n", regs, error_code); local_irq_enable(); if (handle_user_split_lock(regs, error_code)) goto out; do_trap(X86_TRAP_AC, SIGBUS, "alignment check", regs, error_code, BUS_ADRALN, NULL); out: local_irq_disable(); } #ifdef CONFIG_VMAP_STACK __visible void __noreturn handle_stack_overflow(struct pt_regs *regs, unsigned long fault_address, struct stack_info *info) { const char *name = stack_type_name(info->type); printk(KERN_EMERG "BUG: %s stack guard page was hit at %p (stack is %p..%p)\n", name, (void *)fault_address, info->begin, info->end); die("stack guard page", regs, 0); /* Be absolutely certain we don't return. */ panic("%s stack guard hit", name); } #endif /* * Runs on an IST stack for x86_64 and on a special task stack for x86_32. * * On x86_64, this is more or less a normal kernel entry. Notwithstanding the * SDM's warnings about double faults being unrecoverable, returning works as * expected. Presumably what the SDM actually means is that the CPU may get * the register state wrong on entry, so returning could be a bad idea. * * Various CPU engineers have promised that double faults due to an IRET fault * while the stack is read-only are, in fact, recoverable. * * On x86_32, this is entered through a task gate, and regs are synthesized * from the TSS. Returning is, in principle, okay, but changes to regs will * be lost. If, for some reason, we need to return to a context with modified * regs, the shim code could be adjusted to synchronize the registers. * * The 32bit #DF shim provides CR2 already as an argument. On 64bit it needs * to be read before doing anything else. */ DEFINE_IDTENTRY_DF(exc_double_fault) { static const char str[] = "double fault"; struct task_struct *tsk = current; #ifdef CONFIG_VMAP_STACK unsigned long address = read_cr2(); struct stack_info info; #endif #ifdef CONFIG_X86_ESPFIX64 extern unsigned char native_irq_return_iret[]; /* * If IRET takes a non-IST fault on the espfix64 stack, then we * end up promoting it to a doublefault. In that case, take * advantage of the fact that we're not using the normal (TSS.sp0) * stack right now. We can write a fake #GP(0) frame at TSS.sp0 * and then modify our own IRET frame so that, when we return, * we land directly at the #GP(0) vector with the stack already * set up according to its expectations. * * The net result is that our #GP handler will think that we * entered from usermode with the bad user context. * * No need for nmi_enter() here because we don't use RCU. */ if (((long)regs->sp >> P4D_SHIFT) == ESPFIX_PGD_ENTRY && regs->cs == __KERNEL_CS && regs->ip == (unsigned long)native_irq_return_iret) { struct pt_regs *gpregs = (struct pt_regs *)this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1; unsigned long *p = (unsigned long *)regs->sp; /* * regs->sp points to the failing IRET frame on the * ESPFIX64 stack. Copy it to the entry stack. This fills * in gpregs->ss through gpregs->ip. * */ gpregs->ip = p[0]; gpregs->cs = p[1]; gpregs->flags = p[2]; gpregs->sp = p[3]; gpregs->ss = p[4]; gpregs->orig_ax = 0; /* Missing (lost) #GP error code */ /* * Adjust our frame so that we return straight to the #GP * vector with the expected RSP value. This is safe because * we won't enable interrupts or schedule before we invoke * general_protection, so nothing will clobber the stack * frame we just set up. * * We will enter general_protection with kernel GSBASE, * which is what the stub expects, given that the faulting * RIP will be the IRET instruction. */ regs->ip = (unsigned long)asm_exc_general_protection; regs->sp = (unsigned long)&gpregs->orig_ax; return; } #endif irqentry_nmi_enter(regs); instrumentation_begin(); notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_DF, SIGSEGV); tsk->thread.error_code = error_code; tsk->thread.trap_nr = X86_TRAP_DF; #ifdef CONFIG_VMAP_STACK /* * If we overflow the stack into a guard page, the CPU will fail * to deliver #PF and will send #DF instead. Similarly, if we * take any non-IST exception while too close to the bottom of * the stack, the processor will get a page fault while * delivering the exception and will generate a double fault. * * According to the SDM (footnote in 6.15 under "Interrupt 14 - * Page-Fault Exception (#PF): * * Processors update CR2 whenever a page fault is detected. If a * second page fault occurs while an earlier page fault is being * delivered, the faulting linear address of the second fault will * overwrite the contents of CR2 (replacing the previous * address). These updates to CR2 occur even if the page fault * results in a double fault or occurs during the delivery of a * double fault. * * The logic below has a small possibility of incorrectly diagnosing * some errors as stack overflows. For example, if the IDT or GDT * gets corrupted such that #GP delivery fails due to a bad descriptor * causing #GP and we hit this condition while CR2 coincidentally * points to the stack guard page, we'll think we overflowed the * stack. Given that we're going to panic one way or another * if this happens, this isn't necessarily worth fixing. * * If necessary, we could improve the test by only diagnosing * a stack overflow if the saved RSP points within 47 bytes of * the bottom of the stack: if RSP == tsk_stack + 48 and we * take an exception, the stack is already aligned and there * will be enough room SS, RSP, RFLAGS, CS, RIP, and a * possible error code, so a stack overflow would *not* double * fault. With any less space left, exception delivery could * fail, and, as a practical matter, we've overflowed the * stack even if the actual trigger for the double fault was * something else. */ if (get_stack_guard_info((void *)address, &info)) handle_stack_overflow(regs, address, &info); #endif pr_emerg("PANIC: double fault, error_code: 0x%lx\n", error_code); die("double fault", regs, error_code); panic("Machine halted."); instrumentation_end(); } DEFINE_IDTENTRY(exc_bounds) { if (notify_die(DIE_TRAP, "bounds", regs, 0, X86_TRAP_BR, SIGSEGV) == NOTIFY_STOP) return; cond_local_irq_enable(regs); if (!user_mode(regs)) die("bounds", regs, 0); do_trap(X86_TRAP_BR, SIGSEGV, "bounds", regs, 0, 0, NULL); cond_local_irq_disable(regs); } enum kernel_gp_hint { GP_NO_HINT, GP_NON_CANONICAL, GP_CANONICAL }; /* * When an uncaught #GP occurs, try to determine the memory address accessed by * the instruction and return that address to the caller. Also, try to figure * out whether any part of the access to that address was non-canonical. */ static enum kernel_gp_hint get_kernel_gp_address(struct pt_regs *regs, unsigned long *addr) { u8 insn_buf[MAX_INSN_SIZE]; struct insn insn; int ret; if (copy_from_kernel_nofault(insn_buf, (void *)regs->ip, MAX_INSN_SIZE)) return GP_NO_HINT; ret = insn_decode_kernel(&insn, insn_buf); if (ret < 0) return GP_NO_HINT; *addr = (unsigned long)insn_get_addr_ref(&insn, regs); if (*addr == -1UL) return GP_NO_HINT; #ifdef CONFIG_X86_64 /* * Check that: * - the operand is not in the kernel half * - the last byte of the operand is not in the user canonical half */ if (*addr < ~__VIRTUAL_MASK && *addr + insn.opnd_bytes - 1 > __VIRTUAL_MASK) return GP_NON_CANONICAL; #endif return GP_CANONICAL; } #define GPFSTR "general protection fault" static bool fixup_iopl_exception(struct pt_regs *regs) { struct thread_struct *t = ¤t->thread; unsigned char byte; unsigned long ip; if (!IS_ENABLED(CONFIG_X86_IOPL_IOPERM) || t->iopl_emul != 3) return false; if (insn_get_effective_ip(regs, &ip)) return false; if (get_user(byte, (const char __user *)ip)) return false; if (byte != 0xfa && byte != 0xfb) return false; if (!t->iopl_warn && printk_ratelimit()) { pr_err("%s[%d] attempts to use CLI/STI, pretending it's a NOP, ip:%lx", current->comm, task_pid_nr(current), ip); print_vma_addr(KERN_CONT " in ", ip); pr_cont("\n"); t->iopl_warn = 1; } regs->ip += 1; return true; } /* * The unprivileged ENQCMD instruction generates #GPs if the * IA32_PASID MSR has not been populated. If possible, populate * the MSR from a PASID previously allocated to the mm. */ static bool try_fixup_enqcmd_gp(void) { #ifdef CONFIG_ARCH_HAS_CPU_PASID u32 pasid; /* * MSR_IA32_PASID is managed using XSAVE. Directly * writing to the MSR is only possible when fpregs * are valid and the fpstate is not. This is * guaranteed when handling a userspace exception * in *before* interrupts are re-enabled. */ lockdep_assert_irqs_disabled(); /* * Hardware without ENQCMD will not generate * #GPs that can be fixed up here. */ if (!cpu_feature_enabled(X86_FEATURE_ENQCMD)) return false; /* * If the mm has not been allocated a * PASID, the #GP can not be fixed up. */ if (!mm_valid_pasid(current->mm)) return false; pasid = mm_get_enqcmd_pasid(current->mm); /* * Did this thread already have its PASID activated? * If so, the #GP must be from something else. */ if (current->pasid_activated) return false; wrmsrl(MSR_IA32_PASID, pasid | MSR_IA32_PASID_VALID); current->pasid_activated = 1; return true; #else return false; #endif } static bool gp_try_fixup_and_notify(struct pt_regs *regs, int trapnr, unsigned long error_code, const char *str, unsigned long address) { if (fixup_exception(regs, trapnr, error_code, address)) return true; current->thread.error_code = error_code; current->thread.trap_nr = trapnr; /* * To be potentially processing a kprobe fault and to trust the result * from kprobe_running(), we have to be non-preemptible. */ if (!preemptible() && kprobe_running() && kprobe_fault_handler(regs, trapnr)) return true; return notify_die(DIE_GPF, str, regs, error_code, trapnr, SIGSEGV) == NOTIFY_STOP; } static void gp_user_force_sig_segv(struct pt_regs *regs, int trapnr, unsigned long error_code, const char *str) { current->thread.error_code = error_code; current->thread.trap_nr = trapnr; show_signal(current, SIGSEGV, "", str, regs, error_code); force_sig(SIGSEGV); } DEFINE_IDTENTRY_ERRORCODE(exc_general_protection) { char desc[sizeof(GPFSTR) + 50 + 2*sizeof(unsigned long) + 1] = GPFSTR; enum kernel_gp_hint hint = GP_NO_HINT; unsigned long gp_addr; if (user_mode(regs) && try_fixup_enqcmd_gp()) return; cond_local_irq_enable(regs); if (static_cpu_has(X86_FEATURE_UMIP)) { if (user_mode(regs) && fixup_umip_exception(regs)) goto exit; } if (v8086_mode(regs)) { local_irq_enable(); handle_vm86_fault((struct kernel_vm86_regs *) regs, error_code); local_irq_disable(); return; } if (user_mode(regs)) { if (fixup_iopl_exception(regs)) goto exit; if (fixup_vdso_exception(regs, X86_TRAP_GP, error_code, 0)) goto exit; gp_user_force_sig_segv(regs, X86_TRAP_GP, error_code, desc); goto exit; } if (gp_try_fixup_and_notify(regs, X86_TRAP_GP, error_code, desc, 0)) goto exit; if (error_code) snprintf(desc, sizeof(desc), "segment-related " GPFSTR); else hint = get_kernel_gp_address(regs, &gp_addr); if (hint != GP_NO_HINT) snprintf(desc, sizeof(desc), GPFSTR ", %s 0x%lx", (hint == GP_NON_CANONICAL) ? "probably for non-canonical address" : "maybe for address", gp_addr); /* * KASAN is interested only in the non-canonical case, clear it * otherwise. */ if (hint != GP_NON_CANONICAL) gp_addr = 0; die_addr(desc, regs, error_code, gp_addr); exit: cond_local_irq_disable(regs); } static bool do_int3(struct pt_regs *regs) { int res; #ifdef CONFIG_KGDB_LOW_LEVEL_TRAP if (kgdb_ll_trap(DIE_INT3, "int3", regs, 0, X86_TRAP_BP, SIGTRAP) == NOTIFY_STOP) return true; #endif /* CONFIG_KGDB_LOW_LEVEL_TRAP */ #ifdef CONFIG_KPROBES if (kprobe_int3_handler(regs)) return true; #endif res = notify_die(DIE_INT3, "int3", regs, 0, X86_TRAP_BP, SIGTRAP); return res == NOTIFY_STOP; } NOKPROBE_SYMBOL(do_int3); static void do_int3_user(struct pt_regs *regs) { if (do_int3(regs)) return; cond_local_irq_enable(regs); do_trap(X86_TRAP_BP, SIGTRAP, "int3", regs, 0, 0, NULL); cond_local_irq_disable(regs); } DEFINE_IDTENTRY_RAW(exc_int3) { /* * poke_int3_handler() is completely self contained code; it does (and * must) *NOT* call out to anything, lest it hits upon yet another * INT3. */ if (poke_int3_handler(regs)) return; /* * irqentry_enter_from_user_mode() uses static_branch_{,un}likely() * and therefore can trigger INT3, hence poke_int3_handler() must * be done before. If the entry came from kernel mode, then use * nmi_enter() because the INT3 could have been hit in any context * including NMI. */ if (user_mode(regs)) { irqentry_enter_from_user_mode(regs); instrumentation_begin(); do_int3_user(regs); instrumentation_end(); irqentry_exit_to_user_mode(regs); } else { irqentry_state_t irq_state = irqentry_nmi_enter(regs); instrumentation_begin(); if (!do_int3(regs)) die("int3", regs, 0); instrumentation_end(); irqentry_nmi_exit(regs, irq_state); } } #ifdef CONFIG_X86_64 /* * Help handler running on a per-cpu (IST or entry trampoline) stack * to switch to the normal thread stack if the interrupted code was in * user mode. The actual stack switch is done in entry_64.S */ asmlinkage __visible noinstr struct pt_regs *sync_regs(struct pt_regs *eregs) { struct pt_regs *regs = (struct pt_regs *)current_top_of_stack() - 1; if (regs != eregs) *regs = *eregs; return regs; } #ifdef CONFIG_AMD_MEM_ENCRYPT asmlinkage __visible noinstr struct pt_regs *vc_switch_off_ist(struct pt_regs *regs) { unsigned long sp, *stack; struct stack_info info; struct pt_regs *regs_ret; /* * In the SYSCALL entry path the RSP value comes from user-space - don't * trust it and switch to the current kernel stack */ if (ip_within_syscall_gap(regs)) { sp = current_top_of_stack(); goto sync; } /* * From here on the RSP value is trusted. Now check whether entry * happened from a safe stack. Not safe are the entry or unknown stacks, * use the fall-back stack instead in this case. */ sp = regs->sp; stack = (unsigned long *)sp; if (!get_stack_info_noinstr(stack, current, &info) || info.type == STACK_TYPE_ENTRY || info.type > STACK_TYPE_EXCEPTION_LAST) sp = __this_cpu_ist_top_va(VC2); sync: /* * Found a safe stack - switch to it as if the entry didn't happen via * IST stack. The code below only copies pt_regs, the real switch happens * in assembly code. */ sp = ALIGN_DOWN(sp, 8) - sizeof(*regs_ret); regs_ret = (struct pt_regs *)sp; *regs_ret = *regs; return regs_ret; } #endif asmlinkage __visible noinstr struct pt_regs *fixup_bad_iret(struct pt_regs *bad_regs) { struct pt_regs tmp, *new_stack; /* * This is called from entry_64.S early in handling a fault * caused by a bad iret to user mode. To handle the fault * correctly, we want to move our stack frame to where it would * be had we entered directly on the entry stack (rather than * just below the IRET frame) and we want to pretend that the * exception came from the IRET target. */ new_stack = (struct pt_regs *)__this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1; /* Copy the IRET target to the temporary storage. */ __memcpy(&tmp.ip, (void *)bad_regs->sp, 5*8); /* Copy the remainder of the stack from the current stack. */ __memcpy(&tmp, bad_regs, offsetof(struct pt_regs, ip)); /* Update the entry stack */ __memcpy(new_stack, &tmp, sizeof(tmp)); BUG_ON(!user_mode(new_stack)); return new_stack; } #endif static bool is_sysenter_singlestep(struct pt_regs *regs) { /* * We don't try for precision here. If we're anywhere in the region of * code that can be single-stepped in the SYSENTER entry path, then * assume that this is a useless single-step trap due to SYSENTER * being invoked with TF set. (We don't know in advance exactly * which instructions will be hit because BTF could plausibly * be set.) */ #ifdef CONFIG_X86_32 return (regs->ip - (unsigned long)__begin_SYSENTER_singlestep_region) < (unsigned long)__end_SYSENTER_singlestep_region - (unsigned long)__begin_SYSENTER_singlestep_region; #elif defined(CONFIG_IA32_EMULATION) return (regs->ip - (unsigned long)entry_SYSENTER_compat) < (unsigned long)__end_entry_SYSENTER_compat - (unsigned long)entry_SYSENTER_compat; #else return false; #endif } static __always_inline unsigned long debug_read_clear_dr6(void) { unsigned long dr6; /* * The Intel SDM says: * * Certain debug exceptions may clear bits 0-3. The remaining * contents of the DR6 register are never cleared by the * processor. To avoid confusion in identifying debug * exceptions, debug handlers should clear the register before * returning to the interrupted task. * * Keep it simple: clear DR6 immediately. */ get_debugreg(dr6, 6); set_debugreg(DR6_RESERVED, 6); dr6 ^= DR6_RESERVED; /* Flip to positive polarity */ return dr6; } /* * Our handling of the processor debug registers is non-trivial. * We do not clear them on entry and exit from the kernel. Therefore * it is possible to get a watchpoint trap here from inside the kernel. * However, the code in ./ptrace.c has ensured that the user can * only set watchpoints on userspace addresses. Therefore the in-kernel * watchpoint trap can only occur in code which is reading/writing * from user space. Such code must not hold kernel locks (since it * can equally take a page fault), therefore it is safe to call * force_sig_info even though that claims and releases locks. * * Code in ./signal.c ensures that the debug control register * is restored before we deliver any signal, and therefore that * user code runs with the correct debug control register even though * we clear it here. * * Being careful here means that we don't have to be as careful in a * lot of more complicated places (task switching can be a bit lazy * about restoring all the debug state, and ptrace doesn't have to * find every occurrence of the TF bit that could be saved away even * by user code) * * May run on IST stack. */ static bool notify_debug(struct pt_regs *regs, unsigned long *dr6) { /* * Notifiers will clear bits in @dr6 to indicate the event has been * consumed - hw_breakpoint_handler(), single_stop_cont(). * * Notifiers will set bits in @virtual_dr6 to indicate the desire * for signals - ptrace_triggered(), kgdb_hw_overflow_handler(). */ if (notify_die(DIE_DEBUG, "debug", regs, (long)dr6, 0, SIGTRAP) == NOTIFY_STOP) return true; return false; } static noinstr void exc_debug_kernel(struct pt_regs *regs, unsigned long dr6) { /* * Disable breakpoints during exception handling; recursive exceptions * are exceedingly 'fun'. * * Since this function is NOKPROBE, and that also applies to * HW_BREAKPOINT_X, we can't hit a breakpoint before this (XXX except a * HW_BREAKPOINT_W on our stack) * * Entry text is excluded for HW_BP_X and cpu_entry_area, which * includes the entry stack is excluded for everything. * * For FRED, nested #DB should just work fine. But when a watchpoint or * breakpoint is set in the code path which is executed by #DB handler, * it results in an endless recursion and stack overflow. Thus we stay * with the IDT approach, i.e., save DR7 and disable #DB. */ unsigned long dr7 = local_db_save(); irqentry_state_t irq_state = irqentry_nmi_enter(regs); instrumentation_begin(); /* * If something gets miswired and we end up here for a user mode * #DB, we will malfunction. */ WARN_ON_ONCE(user_mode(regs)); if (test_thread_flag(TIF_BLOCKSTEP)) { /* * The SDM says "The processor clears the BTF flag when it * generates a debug exception." but PTRACE_BLOCKSTEP requested * it for userspace, but we just took a kernel #DB, so re-set * BTF. */ unsigned long debugctl; rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl); debugctl |= DEBUGCTLMSR_BTF; wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctl); } /* * Catch SYSENTER with TF set and clear DR_STEP. If this hit a * watchpoint at the same time then that will still be handled. */ if (!cpu_feature_enabled(X86_FEATURE_FRED) && (dr6 & DR_STEP) && is_sysenter_singlestep(regs)) dr6 &= ~DR_STEP; /* * The kernel doesn't use INT1 */ if (!dr6) goto out; if (notify_debug(regs, &dr6)) goto out; /* * The kernel doesn't use TF single-step outside of: * * - Kprobes, consumed through kprobe_debug_handler() * - KGDB, consumed through notify_debug() * * So if we get here with DR_STEP set, something is wonky. * * A known way to trigger this is through QEMU's GDB stub, * which leaks #DB into the guest and causes IST recursion. */ if (WARN_ON_ONCE(dr6 & DR_STEP)) regs->flags &= ~X86_EFLAGS_TF; out: instrumentation_end(); irqentry_nmi_exit(regs, irq_state); local_db_restore(dr7); } static noinstr void exc_debug_user(struct pt_regs *regs, unsigned long dr6) { bool icebp; /* * If something gets miswired and we end up here for a kernel mode * #DB, we will malfunction. */ WARN_ON_ONCE(!user_mode(regs)); /* * NB: We can't easily clear DR7 here because * irqentry_exit_to_usermode() can invoke ptrace, schedule, access * user memory, etc. This means that a recursive #DB is possible. If * this happens, that #DB will hit exc_debug_kernel() and clear DR7. * Since we're not on the IST stack right now, everything will be * fine. */ irqentry_enter_from_user_mode(regs); instrumentation_begin(); /* * Start the virtual/ptrace DR6 value with just the DR_STEP mask * of the real DR6. ptrace_triggered() will set the DR_TRAPn bits. * * Userspace expects DR_STEP to be visible in ptrace_get_debugreg(6) * even if it is not the result of PTRACE_SINGLESTEP. */ current->thread.virtual_dr6 = (dr6 & DR_STEP); /* * The SDM says "The processor clears the BTF flag when it * generates a debug exception." Clear TIF_BLOCKSTEP to keep * TIF_BLOCKSTEP in sync with the hardware BTF flag. */ clear_thread_flag(TIF_BLOCKSTEP); /* * If dr6 has no reason to give us about the origin of this trap, * then it's very likely the result of an icebp/int01 trap. * User wants a sigtrap for that. */ icebp = !dr6; if (notify_debug(regs, &dr6)) goto out; /* It's safe to allow irq's after DR6 has been saved */ local_irq_enable(); if (v8086_mode(regs)) { handle_vm86_trap((struct kernel_vm86_regs *)regs, 0, X86_TRAP_DB); goto out_irq; } /* #DB for bus lock can only be triggered from userspace. */ if (dr6 & DR_BUS_LOCK) handle_bus_lock(regs); /* Add the virtual_dr6 bits for signals. */ dr6 |= current->thread.virtual_dr6; if (dr6 & (DR_STEP | DR_TRAP_BITS) || icebp) send_sigtrap(regs, 0, get_si_code(dr6)); out_irq: local_irq_disable(); out: instrumentation_end(); irqentry_exit_to_user_mode(regs); } #ifdef CONFIG_X86_64 /* IST stack entry */ DEFINE_IDTENTRY_DEBUG(exc_debug) { exc_debug_kernel(regs, debug_read_clear_dr6()); } /* User entry, runs on regular task stack */ DEFINE_IDTENTRY_DEBUG_USER(exc_debug) { exc_debug_user(regs, debug_read_clear_dr6()); } #ifdef CONFIG_X86_FRED /* * When occurred on different ring level, i.e., from user or kernel * context, #DB needs to be handled on different stack: User #DB on * current task stack, while kernel #DB on a dedicated stack. * * This is exactly how FRED event delivery invokes an exception * handler: ring 3 event on level 0 stack, i.e., current task stack; * ring 0 event on the #DB dedicated stack specified in the * IA32_FRED_STKLVLS MSR. So unlike IDT, the FRED debug exception * entry stub doesn't do stack switch. */ DEFINE_FREDENTRY_DEBUG(exc_debug) { /* * FRED #DB stores DR6 on the stack in the format which * debug_read_clear_dr6() returns for the IDT entry points. */ unsigned long dr6 = fred_event_data(regs); if (user_mode(regs)) exc_debug_user(regs, dr6); else exc_debug_kernel(regs, dr6); } #endif /* CONFIG_X86_FRED */ #else /* 32 bit does not have separate entry points. */ DEFINE_IDTENTRY_RAW(exc_debug) { unsigned long dr6 = debug_read_clear_dr6(); if (user_mode(regs)) exc_debug_user(regs, dr6); else exc_debug_kernel(regs, dr6); } #endif /* * Note that we play around with the 'TS' bit in an attempt to get * the correct behaviour even in the presence of the asynchronous * IRQ13 behaviour */ static void math_error(struct pt_regs *regs, int trapnr) { struct task_struct *task = current; struct fpu *fpu = &task->thread.fpu; int si_code; char *str = (trapnr == X86_TRAP_MF) ? "fpu exception" : "simd exception"; cond_local_irq_enable(regs); if (!user_mode(regs)) { if (fixup_exception(regs, trapnr, 0, 0)) goto exit; task->thread.error_code = 0; task->thread.trap_nr = trapnr; if (notify_die(DIE_TRAP, str, regs, 0, trapnr, SIGFPE) != NOTIFY_STOP) die(str, regs, 0); goto exit; } /* * Synchronize the FPU register state to the memory register state * if necessary. This allows the exception handler to inspect it. */ fpu_sync_fpstate(fpu); task->thread.trap_nr = trapnr; task->thread.error_code = 0; si_code = fpu__exception_code(fpu, trapnr); /* Retry when we get spurious exceptions: */ if (!si_code) goto exit; if (fixup_vdso_exception(regs, trapnr, 0, 0)) goto exit; force_sig_fault(SIGFPE, si_code, (void __user *)uprobe_get_trap_addr(regs)); exit: cond_local_irq_disable(regs); } DEFINE_IDTENTRY(exc_coprocessor_error) { math_error(regs, X86_TRAP_MF); } DEFINE_IDTENTRY(exc_simd_coprocessor_error) { if (IS_ENABLED(CONFIG_X86_INVD_BUG)) { /* AMD 486 bug: INVD in CPL 0 raises #XF instead of #GP */ if (!static_cpu_has(X86_FEATURE_XMM)) { __exc_general_protection(regs, 0); return; } } math_error(regs, X86_TRAP_XF); } DEFINE_IDTENTRY(exc_spurious_interrupt_bug) { /* * This addresses a Pentium Pro Erratum: * * PROBLEM: If the APIC subsystem is configured in mixed mode with * Virtual Wire mode implemented through the local APIC, an * interrupt vector of 0Fh (Intel reserved encoding) may be * generated by the local APIC (Int 15). This vector may be * generated upon receipt of a spurious interrupt (an interrupt * which is removed before the system receives the INTA sequence) * instead of the programmed 8259 spurious interrupt vector. * * IMPLICATION: The spurious interrupt vector programmed in the * 8259 is normally handled by an operating system's spurious * interrupt handler. However, a vector of 0Fh is unknown to some * operating systems, which would crash if this erratum occurred. * * In theory this could be limited to 32bit, but the handler is not * hurting and who knows which other CPUs suffer from this. */ } static bool handle_xfd_event(struct pt_regs *regs) { u64 xfd_err; int err; if (!IS_ENABLED(CONFIG_X86_64) || !cpu_feature_enabled(X86_FEATURE_XFD)) return false; rdmsrl(MSR_IA32_XFD_ERR, xfd_err); if (!xfd_err) return false; wrmsrl(MSR_IA32_XFD_ERR, 0); /* Die if that happens in kernel space */ if (WARN_ON(!user_mode(regs))) return false; local_irq_enable(); err = xfd_enable_feature(xfd_err); switch (err) { case -EPERM: force_sig_fault(SIGILL, ILL_ILLOPC, error_get_trap_addr(regs)); break; case -EFAULT: force_sig(SIGSEGV); break; } local_irq_disable(); return true; } DEFINE_IDTENTRY(exc_device_not_available) { unsigned long cr0 = read_cr0(); if (handle_xfd_event(regs)) return; #ifdef CONFIG_MATH_EMULATION if (!boot_cpu_has(X86_FEATURE_FPU) && (cr0 & X86_CR0_EM)) { struct math_emu_info info = { }; cond_local_irq_enable(regs); info.regs = regs; math_emulate(&info); cond_local_irq_disable(regs); return; } #endif /* This should not happen. */ if (WARN(cr0 & X86_CR0_TS, "CR0.TS was set")) { /* Try to fix it up and carry on. */ write_cr0(cr0 & ~X86_CR0_TS); } else { /* * Something terrible happened, and we're better off trying * to kill the task than getting stuck in a never-ending * loop of #NM faults. */ die("unexpected #NM exception", regs, 0); } } #ifdef CONFIG_INTEL_TDX_GUEST #define VE_FAULT_STR "VE fault" static void ve_raise_fault(struct pt_regs *regs, long error_code, unsigned long address) { if (user_mode(regs)) { gp_user_force_sig_segv(regs, X86_TRAP_VE, error_code, VE_FAULT_STR); return; } if (gp_try_fixup_and_notify(regs, X86_TRAP_VE, error_code, VE_FAULT_STR, address)) { return; } die_addr(VE_FAULT_STR, regs, error_code, address); } /* * Virtualization Exceptions (#VE) are delivered to TDX guests due to * specific guest actions which may happen in either user space or the * kernel: * * * Specific instructions (WBINVD, for example) * * Specific MSR accesses * * Specific CPUID leaf accesses * * Access to specific guest physical addresses * * In the settings that Linux will run in, virtualization exceptions are * never generated on accesses to normal, TD-private memory that has been * accepted (by BIOS or with tdx_enc_status_changed()). * * Syscall entry code has a critical window where the kernel stack is not * yet set up. Any exception in this window leads to hard to debug issues * and can be exploited for privilege escalation. Exceptions in the NMI * entry code also cause issues. Returning from the exception handler with * IRET will re-enable NMIs and nested NMI will corrupt the NMI stack. * * For these reasons, the kernel avoids #VEs during the syscall gap and * the NMI entry code. Entry code paths do not access TD-shared memory, * MMIO regions, use #VE triggering MSRs, instructions, or CPUID leaves * that might generate #VE. VMM can remove memory from TD at any point, * but access to unaccepted (or missing) private memory leads to VM * termination, not to #VE. * * Similarly to page faults and breakpoints, #VEs are allowed in NMI * handlers once the kernel is ready to deal with nested NMIs. * * During #VE delivery, all interrupts, including NMIs, are blocked until * TDGETVEINFO is called. It prevents #VE nesting until the kernel reads * the VE info. * * If a guest kernel action which would normally cause a #VE occurs in * the interrupt-disabled region before TDGETVEINFO, a #DF (fault * exception) is delivered to the guest which will result in an oops. * * The entry code has been audited carefully for following these expectations. * Changes in the entry code have to be audited for correctness vs. this * aspect. Similarly to #PF, #VE in these places will expose kernel to * privilege escalation or may lead to random crashes. */ DEFINE_IDTENTRY(exc_virtualization_exception) { struct ve_info ve; /* * NMIs/Machine-checks/Interrupts will be in a disabled state * till TDGETVEINFO TDCALL is executed. This ensures that VE * info cannot be overwritten by a nested #VE. */ tdx_get_ve_info(&ve); cond_local_irq_enable(regs); /* * If tdx_handle_virt_exception() could not process * it successfully, treat it as #GP(0) and handle it. */ if (!tdx_handle_virt_exception(regs, &ve)) ve_raise_fault(regs, 0, ve.gla); cond_local_irq_disable(regs); } #endif #ifdef CONFIG_X86_32 DEFINE_IDTENTRY_SW(iret_error) { local_irq_enable(); if (notify_die(DIE_TRAP, "iret exception", regs, 0, X86_TRAP_IRET, SIGILL) != NOTIFY_STOP) { do_trap(X86_TRAP_IRET, SIGILL, "iret exception", regs, 0, ILL_BADSTK, (void __user *)NULL); } local_irq_disable(); } #endif /* Do not enable FRED by default yet. */ static bool enable_fred __ro_after_init = false; #ifdef CONFIG_X86_FRED static int __init fred_setup(char *str) { if (!str) return -EINVAL; if (!cpu_feature_enabled(X86_FEATURE_FRED)) return 0; if (!strcmp(str, "on")) enable_fred = true; else if (!strcmp(str, "off")) enable_fred = false; else pr_warn("invalid FRED option: 'fred=%s'\n", str); return 0; } early_param("fred", fred_setup); #endif void __init trap_init(void) { if (cpu_feature_enabled(X86_FEATURE_FRED) && !enable_fred) setup_clear_cpu_cap(X86_FEATURE_FRED); /* Init cpu_entry_area before IST entries are set up */ setup_cpu_entry_areas(); /* Init GHCB memory pages when running as an SEV-ES guest */ sev_es_init_vc_handling(); /* Initialize TSS before setting up traps so ISTs work */ cpu_init_exception_handling(); /* Setup traps as cpu_init() might #GP */ if (!cpu_feature_enabled(X86_FEATURE_FRED)) idt_setup_traps(); cpu_init(); }