diff options
Diffstat (limited to 'arch/x86/kernel/traps.c')
| -rw-r--r-- | arch/x86/kernel/traps.c | 1189 |
1 files changed, 1189 insertions, 0 deletions
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c new file mode 100644 index 000000000..98838b784 --- /dev/null +++ b/arch/x86/kernel/traps.c @@ -0,0 +1,1189 @@ +/* + * Copyright (C) 1991, 1992 Linus Torvalds + * Copyright (C) 2000, 2001, 2002 Andi Kleen, SuSE Labs + * + * Pentium III FXSR, SSE support + * Gareth Hughes <gareth@valinux.com>, May 2000 + */ + +/* + * Handle hardware traps and faults. + */ + +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include <linux/context_tracking.h> +#include <linux/interrupt.h> +#include <linux/kallsyms.h> +#include <linux/spinlock.h> +#include <linux/kprobes.h> +#include <linux/uaccess.h> +#include <linux/kdebug.h> +#include <linux/kgdb.h> +#include <linux/kernel.h> +#include <linux/export.h> +#include <linux/ptrace.h> +#include <linux/uprobes.h> +#include <linux/string.h> +#include <linux/delay.h> +#include <linux/errno.h> +#include <linux/kexec.h> +#include <linux/sched.h> +#include <linux/sched/task_stack.h> +#include <linux/timer.h> +#include <linux/init.h> +#include <linux/bug.h> +#include <linux/nmi.h> +#include <linux/mm.h> +#include <linux/smp.h> +#include <linux/io.h> +#include <linux/hardirq.h> +#include <linux/atomic.h> + +#include <asm/stacktrace.h> +#include <asm/processor.h> +#include <asm/debugreg.h> +#include <asm/realmode.h> +#include <asm/text-patching.h> +#include <asm/ftrace.h> +#include <asm/traps.h> +#include <asm/desc.h> +#include <asm/fpu/internal.h> +#include <asm/cpu.h> +#include <asm/cpu_entry_area.h> +#include <asm/mce.h> +#include <asm/fixmap.h> +#include <asm/mach_traps.h> +#include <asm/alternative.h> +#include <asm/fpu/xstate.h> +#include <asm/vm86.h> +#include <asm/umip.h> +#include <asm/insn.h> +#include <asm/insn-eval.h> + +#ifdef CONFIG_X86_64 +#include <asm/x86_init.h> +#include <asm/proto.h> +#else +#include <asm/processor-flags.h> +#include <asm/setup.h> +#include <asm/proto.h> +#endif + +DECLARE_BITMAP(system_vectors, NR_VECTORS); + +static inline void cond_local_irq_enable(struct pt_regs *regs) +{ + if (regs->flags & X86_EFLAGS_IF) + local_irq_enable(); +} + +static inline void cond_local_irq_disable(struct pt_regs *regs) +{ + if (regs->flags & X86_EFLAGS_IF) + local_irq_disable(); +} + +__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); + } + + /* + * 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; + + 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) { + 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(const char *message, + struct pt_regs *regs, + unsigned long fault_address) +{ + printk(KERN_EMERG "BUG: stack guard page was hit at %p (stack is %p..%p)\n", + (void *)fault_address, current->stack, + (char *)current->stack + THREAD_SIZE - 1); + die(message, regs, 0); + + /* Be absolutely certain we don't return. */ + panic("%s", message); +} +#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(); +#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 interupts 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 ((unsigned long)task_stack_page(tsk) - 1 - address < PAGE_SIZE) { + handle_stack_overflow("kernel stack overflow (double-fault)", + regs, address); + } +#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; + + if (copy_from_kernel_nofault(insn_buf, (void *)regs->ip, + MAX_INSN_SIZE)) + return GP_NO_HINT; + + kernel_insn_init(&insn, insn_buf, MAX_INSN_SIZE); + insn_get_modrm(&insn); + insn_get_sib(&insn); + + *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; + + ip = insn_get_effective_ip(regs); + if (!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; +} + +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; + struct task_struct *tsk; + unsigned long gp_addr; + int ret; + + 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; + } + + tsk = current; + + if (user_mode(regs)) { + if (fixup_iopl_exception(regs)) + goto exit; + + tsk->thread.error_code = error_code; + tsk->thread.trap_nr = X86_TRAP_GP; + + show_signal(tsk, SIGSEGV, "", desc, regs, error_code); + force_sig(SIGSEGV); + goto exit; + } + + if (fixup_exception(regs, X86_TRAP_GP, error_code, 0)) + goto exit; + + tsk->thread.error_code = error_code; + tsk->thread.trap_nr = X86_TRAP_GP; + + /* + * 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, X86_TRAP_GP)) + goto exit; + + ret = notify_die(DIE_GPF, desc, regs, error_code, X86_TRAP_GP, SIGSEGV); + if (ret == NOTIFY_STOP) + 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 *)this_cpu_read(cpu_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 = this_cpu_read(cpu_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 + +struct bad_iret_stack { + void *error_entry_ret; + struct pt_regs regs; +}; + +asmlinkage __visible noinstr +struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s) +{ + /* + * 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. + */ + struct bad_iret_stack tmp, *new_stack = + (struct bad_iret_stack *)__this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1; + + /* Copy the IRET target to the temporary storage. */ + __memcpy(&tmp.regs.ip, (void *)s->regs.sp, 5*8); + + /* Copy the remainder of the stack from the current stack. */ + __memcpy(&tmp, s, offsetof(struct bad_iret_stack, regs.ip)); + + /* Update the entry stack */ + __memcpy(new_stack, &tmp, sizeof(tmp)); + + BUG_ON(!user_mode(&new_stack->regs)); + 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 __always_inline 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. + */ + 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 ((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 __always_inline 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; + } + + /* 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()); +} +#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; + } + + /* + * Save the info for the exception handler and clear the error. + */ + fpu__save(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; + + 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. + */ +} + +DEFINE_IDTENTRY(exc_device_not_available) +{ + unsigned long cr0 = read_cr0(); + +#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_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 + +void __init trap_init(void) +{ + /* 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(); + + idt_setup_traps(); + + cpu_init_exception_handling(); + cpu_init(); + + idt_setup_ist_traps(); +} |