| #include <linux/extable.h> |
| #include <linux/uaccess.h> |
| #include <linux/sched/debug.h> |
| |
| #include <asm/fpu/internal.h> |
| #include <asm/traps.h> |
| #include <asm/kdebug.h> |
| |
| typedef bool (*ex_handler_t)(const struct exception_table_entry *, |
| struct pt_regs *, int); |
| |
| static inline unsigned long |
| ex_fixup_addr(const struct exception_table_entry *x) |
| { |
| return (unsigned long)&x->fixup + x->fixup; |
| } |
| static inline ex_handler_t |
| ex_fixup_handler(const struct exception_table_entry *x) |
| { |
| return (ex_handler_t)((unsigned long)&x->handler + x->handler); |
| } |
| |
| bool ex_handler_default(const struct exception_table_entry *fixup, |
| struct pt_regs *regs, int trapnr) |
| { |
| regs->ip = ex_fixup_addr(fixup); |
| return true; |
| } |
| EXPORT_SYMBOL(ex_handler_default); |
| |
| bool ex_handler_fault(const struct exception_table_entry *fixup, |
| struct pt_regs *regs, int trapnr) |
| { |
| regs->ip = ex_fixup_addr(fixup); |
| regs->ax = trapnr; |
| return true; |
| } |
| EXPORT_SYMBOL_GPL(ex_handler_fault); |
| |
| /* |
| * Handler for UD0 exception following a failed test against the |
| * result of a refcount inc/dec/add/sub. |
| */ |
| bool ex_handler_refcount(const struct exception_table_entry *fixup, |
| struct pt_regs *regs, int trapnr) |
| { |
| /* First unconditionally saturate the refcount. */ |
| *(int *)regs->cx = INT_MIN / 2; |
| |
| /* |
| * Strictly speaking, this reports the fixup destination, not |
| * the fault location, and not the actually overflowing |
| * instruction, which is the instruction before the "js", but |
| * since that instruction could be a variety of lengths, just |
| * report the location after the overflow, which should be close |
| * enough for finding the overflow, as it's at least back in |
| * the function, having returned from .text.unlikely. |
| */ |
| regs->ip = ex_fixup_addr(fixup); |
| |
| /* |
| * This function has been called because either a negative refcount |
| * value was seen by any of the refcount functions, or a zero |
| * refcount value was seen by refcount_dec(). |
| * |
| * If we crossed from INT_MAX to INT_MIN, OF (Overflow Flag: result |
| * wrapped around) will be set. Additionally, seeing the refcount |
| * reach 0 will set ZF (Zero Flag: result was zero). In each of |
| * these cases we want a report, since it's a boundary condition. |
| * The SF case is not reported since it indicates post-boundary |
| * manipulations below zero or above INT_MAX. And if none of the |
| * flags are set, something has gone very wrong, so report it. |
| */ |
| if (regs->flags & (X86_EFLAGS_OF | X86_EFLAGS_ZF)) { |
| bool zero = regs->flags & X86_EFLAGS_ZF; |
| |
| refcount_error_report(regs, zero ? "hit zero" : "overflow"); |
| } else if ((regs->flags & X86_EFLAGS_SF) == 0) { |
| /* Report if none of OF, ZF, nor SF are set. */ |
| refcount_error_report(regs, "unexpected saturation"); |
| } |
| |
| return true; |
| } |
| EXPORT_SYMBOL_GPL(ex_handler_refcount); |
| |
| /* |
| * Handler for when we fail to restore a task's FPU state. We should never get |
| * here because the FPU state of a task using the FPU (task->thread.fpu.state) |
| * should always be valid. However, past bugs have allowed userspace to set |
| * reserved bits in the XSAVE area using PTRACE_SETREGSET or sys_rt_sigreturn(). |
| * These caused XRSTOR to fail when switching to the task, leaking the FPU |
| * registers of the task previously executing on the CPU. Mitigate this class |
| * of vulnerability by restoring from the initial state (essentially, zeroing |
| * out all the FPU registers) if we can't restore from the task's FPU state. |
| */ |
| bool ex_handler_fprestore(const struct exception_table_entry *fixup, |
| struct pt_regs *regs, int trapnr) |
| { |
| regs->ip = ex_fixup_addr(fixup); |
| |
| WARN_ONCE(1, "Bad FPU state detected at %pB, reinitializing FPU registers.", |
| (void *)instruction_pointer(regs)); |
| |
| __copy_kernel_to_fpregs(&init_fpstate, -1); |
| return true; |
| } |
| EXPORT_SYMBOL_GPL(ex_handler_fprestore); |
| |
| bool ex_handler_ext(const struct exception_table_entry *fixup, |
| struct pt_regs *regs, int trapnr) |
| { |
| /* Special hack for uaccess_err */ |
| current->thread.uaccess_err = 1; |
| regs->ip = ex_fixup_addr(fixup); |
| return true; |
| } |
| EXPORT_SYMBOL(ex_handler_ext); |
| |
| bool ex_handler_rdmsr_unsafe(const struct exception_table_entry *fixup, |
| struct pt_regs *regs, int trapnr) |
| { |
| if (pr_warn_once("unchecked MSR access error: RDMSR from 0x%x at rIP: 0x%lx (%pF)\n", |
| (unsigned int)regs->cx, regs->ip, (void *)regs->ip)) |
| show_stack_regs(regs); |
| |
| /* Pretend that the read succeeded and returned 0. */ |
| regs->ip = ex_fixup_addr(fixup); |
| regs->ax = 0; |
| regs->dx = 0; |
| return true; |
| } |
| EXPORT_SYMBOL(ex_handler_rdmsr_unsafe); |
| |
| bool ex_handler_wrmsr_unsafe(const struct exception_table_entry *fixup, |
| struct pt_regs *regs, int trapnr) |
| { |
| if (pr_warn_once("unchecked MSR access error: WRMSR to 0x%x (tried to write 0x%08x%08x) at rIP: 0x%lx (%pF)\n", |
| (unsigned int)regs->cx, (unsigned int)regs->dx, |
| (unsigned int)regs->ax, regs->ip, (void *)regs->ip)) |
| show_stack_regs(regs); |
| |
| /* Pretend that the write succeeded. */ |
| regs->ip = ex_fixup_addr(fixup); |
| return true; |
| } |
| EXPORT_SYMBOL(ex_handler_wrmsr_unsafe); |
| |
| bool ex_handler_clear_fs(const struct exception_table_entry *fixup, |
| struct pt_regs *regs, int trapnr) |
| { |
| if (static_cpu_has(X86_BUG_NULL_SEG)) |
| asm volatile ("mov %0, %%fs" : : "rm" (__USER_DS)); |
| asm volatile ("mov %0, %%fs" : : "rm" (0)); |
| return ex_handler_default(fixup, regs, trapnr); |
| } |
| EXPORT_SYMBOL(ex_handler_clear_fs); |
| |
| bool ex_has_fault_handler(unsigned long ip) |
| { |
| const struct exception_table_entry *e; |
| ex_handler_t handler; |
| |
| e = search_exception_tables(ip); |
| if (!e) |
| return false; |
| handler = ex_fixup_handler(e); |
| |
| return handler == ex_handler_fault; |
| } |
| |
| int fixup_exception(struct pt_regs *regs, int trapnr) |
| { |
| const struct exception_table_entry *e; |
| ex_handler_t handler; |
| |
| #ifdef CONFIG_PNPBIOS |
| if (unlikely(SEGMENT_IS_PNP_CODE(regs->cs))) { |
| extern u32 pnp_bios_fault_eip, pnp_bios_fault_esp; |
| extern u32 pnp_bios_is_utter_crap; |
| pnp_bios_is_utter_crap = 1; |
| printk(KERN_CRIT "PNPBIOS fault.. attempting recovery.\n"); |
| __asm__ volatile( |
| "movl %0, %%esp\n\t" |
| "jmp *%1\n\t" |
| : : "g" (pnp_bios_fault_esp), "g" (pnp_bios_fault_eip)); |
| panic("do_trap: can't hit this"); |
| } |
| #endif |
| |
| e = search_exception_tables(regs->ip); |
| if (!e) |
| return 0; |
| |
| handler = ex_fixup_handler(e); |
| return handler(e, regs, trapnr); |
| } |
| |
| extern unsigned int early_recursion_flag; |
| |
| /* Restricted version used during very early boot */ |
| void __init early_fixup_exception(struct pt_regs *regs, int trapnr) |
| { |
| /* Ignore early NMIs. */ |
| if (trapnr == X86_TRAP_NMI) |
| return; |
| |
| if (early_recursion_flag > 2) |
| goto halt_loop; |
| |
| /* |
| * Old CPUs leave the high bits of CS on the stack |
| * undefined. I'm not sure which CPUs do this, but at least |
| * the 486 DX works this way. |
| */ |
| if (regs->cs != __KERNEL_CS) |
| goto fail; |
| |
| /* |
| * The full exception fixup machinery is available as soon as |
| * the early IDT is loaded. This means that it is the |
| * responsibility of extable users to either function correctly |
| * when handlers are invoked early or to simply avoid causing |
| * exceptions before they're ready to handle them. |
| * |
| * This is better than filtering which handlers can be used, |
| * because refusing to call a handler here is guaranteed to |
| * result in a hard-to-debug panic. |
| * |
| * Keep in mind that not all vectors actually get here. Early |
| * fage faults, for example, are special. |
| */ |
| if (fixup_exception(regs, trapnr)) |
| return; |
| |
| if (fixup_bug(regs, trapnr)) |
| return; |
| |
| fail: |
| early_printk("PANIC: early exception 0x%02x IP %lx:%lx error %lx cr2 0x%lx\n", |
| (unsigned)trapnr, (unsigned long)regs->cs, regs->ip, |
| regs->orig_ax, read_cr2()); |
| |
| show_regs(regs); |
| |
| halt_loop: |
| while (true) |
| halt(); |
| } |