diff options
Diffstat (limited to 'arch/x86/mm/fault.c')
| -rw-r--r-- | arch/x86/mm/fault.c | 1490 |
1 files changed, 1490 insertions, 0 deletions
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c new file mode 100644 index 000000000..c61acf635 --- /dev/null +++ b/arch/x86/mm/fault.c @@ -0,0 +1,1490 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 1995 Linus Torvalds + * Copyright (C) 2001, 2002 Andi Kleen, SuSE Labs. + * Copyright (C) 2008-2009, Red Hat Inc., Ingo Molnar + */ +#include <linux/sched.h> /* test_thread_flag(), ... */ +#include <linux/sched/task_stack.h> /* task_stack_*(), ... */ +#include <linux/kdebug.h> /* oops_begin/end, ... */ +#include <linux/extable.h> /* search_exception_tables */ +#include <linux/bootmem.h> /* max_low_pfn */ +#include <linux/kprobes.h> /* NOKPROBE_SYMBOL, ... */ +#include <linux/mmiotrace.h> /* kmmio_handler, ... */ +#include <linux/perf_event.h> /* perf_sw_event */ +#include <linux/hugetlb.h> /* hstate_index_to_shift */ +#include <linux/prefetch.h> /* prefetchw */ +#include <linux/context_tracking.h> /* exception_enter(), ... */ +#include <linux/uaccess.h> /* faulthandler_disabled() */ +#include <linux/mm_types.h> + +#include <asm/cpufeature.h> /* boot_cpu_has, ... */ +#include <asm/traps.h> /* dotraplinkage, ... */ +#include <asm/pgalloc.h> /* pgd_*(), ... */ +#include <asm/fixmap.h> /* VSYSCALL_ADDR */ +#include <asm/vsyscall.h> /* emulate_vsyscall */ +#include <asm/vm86.h> /* struct vm86 */ +#include <asm/mmu_context.h> /* vma_pkey() */ + +#define CREATE_TRACE_POINTS +#include <asm/trace/exceptions.h> + +/* + * Returns 0 if mmiotrace is disabled, or if the fault is not + * handled by mmiotrace: + */ +static nokprobe_inline int +kmmio_fault(struct pt_regs *regs, unsigned long addr) +{ + if (unlikely(is_kmmio_active())) + if (kmmio_handler(regs, addr) == 1) + return -1; + return 0; +} + +static nokprobe_inline int kprobes_fault(struct pt_regs *regs) +{ + int ret = 0; + + /* kprobe_running() needs smp_processor_id() */ + if (kprobes_built_in() && !user_mode(regs)) { + preempt_disable(); + if (kprobe_running() && kprobe_fault_handler(regs, 14)) + ret = 1; + preempt_enable(); + } + + return ret; +} + +/* + * Prefetch quirks: + * + * 32-bit mode: + * + * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch. + * Check that here and ignore it. + * + * 64-bit mode: + * + * Sometimes the CPU reports invalid exceptions on prefetch. + * Check that here and ignore it. + * + * Opcode checker based on code by Richard Brunner. + */ +static inline int +check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr, + unsigned char opcode, int *prefetch) +{ + unsigned char instr_hi = opcode & 0xf0; + unsigned char instr_lo = opcode & 0x0f; + + switch (instr_hi) { + case 0x20: + case 0x30: + /* + * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes. + * In X86_64 long mode, the CPU will signal invalid + * opcode if some of these prefixes are present so + * X86_64 will never get here anyway + */ + return ((instr_lo & 7) == 0x6); +#ifdef CONFIG_X86_64 + case 0x40: + /* + * In AMD64 long mode 0x40..0x4F are valid REX prefixes + * Need to figure out under what instruction mode the + * instruction was issued. Could check the LDT for lm, + * but for now it's good enough to assume that long + * mode only uses well known segments or kernel. + */ + return (!user_mode(regs) || user_64bit_mode(regs)); +#endif + case 0x60: + /* 0x64 thru 0x67 are valid prefixes in all modes. */ + return (instr_lo & 0xC) == 0x4; + case 0xF0: + /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */ + return !instr_lo || (instr_lo>>1) == 1; + case 0x00: + /* Prefetch instruction is 0x0F0D or 0x0F18 */ + if (probe_kernel_address(instr, opcode)) + return 0; + + *prefetch = (instr_lo == 0xF) && + (opcode == 0x0D || opcode == 0x18); + return 0; + default: + return 0; + } +} + +static int +is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr) +{ + unsigned char *max_instr; + unsigned char *instr; + int prefetch = 0; + + /* + * If it was a exec (instruction fetch) fault on NX page, then + * do not ignore the fault: + */ + if (error_code & X86_PF_INSTR) + return 0; + + instr = (void *)convert_ip_to_linear(current, regs); + max_instr = instr + 15; + + if (user_mode(regs) && instr >= (unsigned char *)TASK_SIZE_MAX) + return 0; + + while (instr < max_instr) { + unsigned char opcode; + + if (probe_kernel_address(instr, opcode)) + break; + + instr++; + + if (!check_prefetch_opcode(regs, instr, opcode, &prefetch)) + break; + } + return prefetch; +} + +/* + * A protection key fault means that the PKRU value did not allow + * access to some PTE. Userspace can figure out what PKRU was + * from the XSAVE state, and this function fills out a field in + * siginfo so userspace can discover which protection key was set + * on the PTE. + * + * If we get here, we know that the hardware signaled a X86_PF_PK + * fault and that there was a VMA once we got in the fault + * handler. It does *not* guarantee that the VMA we find here + * was the one that we faulted on. + * + * 1. T1 : mprotect_key(foo, PAGE_SIZE, pkey=4); + * 2. T1 : set PKRU to deny access to pkey=4, touches page + * 3. T1 : faults... + * 4. T2: mprotect_key(foo, PAGE_SIZE, pkey=5); + * 5. T1 : enters fault handler, takes mmap_sem, etc... + * 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really + * faulted on a pte with its pkey=4. + */ +static void fill_sig_info_pkey(int si_signo, int si_code, siginfo_t *info, + u32 *pkey) +{ + /* This is effectively an #ifdef */ + if (!boot_cpu_has(X86_FEATURE_OSPKE)) + return; + + /* Fault not from Protection Keys: nothing to do */ + if ((si_code != SEGV_PKUERR) || (si_signo != SIGSEGV)) + return; + /* + * force_sig_info_fault() is called from a number of + * contexts, some of which have a VMA and some of which + * do not. The X86_PF_PK handing happens after we have a + * valid VMA, so we should never reach this without a + * valid VMA. + */ + if (!pkey) { + WARN_ONCE(1, "PKU fault with no VMA passed in"); + info->si_pkey = 0; + return; + } + /* + * si_pkey should be thought of as a strong hint, but not + * absolutely guranteed to be 100% accurate because of + * the race explained above. + */ + info->si_pkey = *pkey; +} + +static void +force_sig_info_fault(int si_signo, int si_code, unsigned long address, + struct task_struct *tsk, u32 *pkey, int fault) +{ + unsigned lsb = 0; + siginfo_t info; + + clear_siginfo(&info); + info.si_signo = si_signo; + info.si_errno = 0; + info.si_code = si_code; + info.si_addr = (void __user *)address; + if (fault & VM_FAULT_HWPOISON_LARGE) + lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault)); + if (fault & VM_FAULT_HWPOISON) + lsb = PAGE_SHIFT; + info.si_addr_lsb = lsb; + + fill_sig_info_pkey(si_signo, si_code, &info, pkey); + + force_sig_info(si_signo, &info, tsk); +} + +DEFINE_SPINLOCK(pgd_lock); +LIST_HEAD(pgd_list); + +#ifdef CONFIG_X86_32 +static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address) +{ + unsigned index = pgd_index(address); + pgd_t *pgd_k; + p4d_t *p4d, *p4d_k; + pud_t *pud, *pud_k; + pmd_t *pmd, *pmd_k; + + pgd += index; + pgd_k = init_mm.pgd + index; + + if (!pgd_present(*pgd_k)) + return NULL; + + /* + * set_pgd(pgd, *pgd_k); here would be useless on PAE + * and redundant with the set_pmd() on non-PAE. As would + * set_p4d/set_pud. + */ + p4d = p4d_offset(pgd, address); + p4d_k = p4d_offset(pgd_k, address); + if (!p4d_present(*p4d_k)) + return NULL; + + pud = pud_offset(p4d, address); + pud_k = pud_offset(p4d_k, address); + if (!pud_present(*pud_k)) + return NULL; + + pmd = pmd_offset(pud, address); + pmd_k = pmd_offset(pud_k, address); + + if (pmd_present(*pmd) != pmd_present(*pmd_k)) + set_pmd(pmd, *pmd_k); + + if (!pmd_present(*pmd_k)) + return NULL; + else + BUG_ON(pmd_pfn(*pmd) != pmd_pfn(*pmd_k)); + + return pmd_k; +} + +static void vmalloc_sync(void) +{ + unsigned long address; + + if (SHARED_KERNEL_PMD) + return; + + for (address = VMALLOC_START & PMD_MASK; + address >= TASK_SIZE_MAX && address < VMALLOC_END; + address += PMD_SIZE) { + struct page *page; + + spin_lock(&pgd_lock); + list_for_each_entry(page, &pgd_list, lru) { + spinlock_t *pgt_lock; + + /* the pgt_lock only for Xen */ + pgt_lock = &pgd_page_get_mm(page)->page_table_lock; + + spin_lock(pgt_lock); + vmalloc_sync_one(page_address(page), address); + spin_unlock(pgt_lock); + } + spin_unlock(&pgd_lock); + } +} + +void vmalloc_sync_mappings(void) +{ + vmalloc_sync(); +} + +void vmalloc_sync_unmappings(void) +{ + vmalloc_sync(); +} + +/* + * 32-bit: + * + * Handle a fault on the vmalloc or module mapping area + */ +static noinline int vmalloc_fault(unsigned long address) +{ + unsigned long pgd_paddr; + pmd_t *pmd_k; + pte_t *pte_k; + + /* Make sure we are in vmalloc area: */ + if (!(address >= VMALLOC_START && address < VMALLOC_END)) + return -1; + + /* + * Synchronize this task's top level page-table + * with the 'reference' page table. + * + * Do _not_ use "current" here. We might be inside + * an interrupt in the middle of a task switch.. + */ + pgd_paddr = read_cr3_pa(); + pmd_k = vmalloc_sync_one(__va(pgd_paddr), address); + if (!pmd_k) + return -1; + + if (pmd_large(*pmd_k)) + return 0; + + pte_k = pte_offset_kernel(pmd_k, address); + if (!pte_present(*pte_k)) + return -1; + + return 0; +} +NOKPROBE_SYMBOL(vmalloc_fault); + +/* + * Did it hit the DOS screen memory VA from vm86 mode? + */ +static inline void +check_v8086_mode(struct pt_regs *regs, unsigned long address, + struct task_struct *tsk) +{ +#ifdef CONFIG_VM86 + unsigned long bit; + + if (!v8086_mode(regs) || !tsk->thread.vm86) + return; + + bit = (address - 0xA0000) >> PAGE_SHIFT; + if (bit < 32) + tsk->thread.vm86->screen_bitmap |= 1 << bit; +#endif +} + +static bool low_pfn(unsigned long pfn) +{ + return pfn < max_low_pfn; +} + +static void dump_pagetable(unsigned long address) +{ + pgd_t *base = __va(read_cr3_pa()); + pgd_t *pgd = &base[pgd_index(address)]; + p4d_t *p4d; + pud_t *pud; + pmd_t *pmd; + pte_t *pte; + +#ifdef CONFIG_X86_PAE + pr_info("*pdpt = %016Lx ", pgd_val(*pgd)); + if (!low_pfn(pgd_val(*pgd) >> PAGE_SHIFT) || !pgd_present(*pgd)) + goto out; +#define pr_pde pr_cont +#else +#define pr_pde pr_info +#endif + p4d = p4d_offset(pgd, address); + pud = pud_offset(p4d, address); + pmd = pmd_offset(pud, address); + pr_pde("*pde = %0*Lx ", sizeof(*pmd) * 2, (u64)pmd_val(*pmd)); +#undef pr_pde + + /* + * We must not directly access the pte in the highpte + * case if the page table is located in highmem. + * And let's rather not kmap-atomic the pte, just in case + * it's allocated already: + */ + if (!low_pfn(pmd_pfn(*pmd)) || !pmd_present(*pmd) || pmd_large(*pmd)) + goto out; + + pte = pte_offset_kernel(pmd, address); + pr_cont("*pte = %0*Lx ", sizeof(*pte) * 2, (u64)pte_val(*pte)); +out: + pr_cont("\n"); +} + +#else /* CONFIG_X86_64: */ + +void vmalloc_sync_mappings(void) +{ + /* + * 64-bit mappings might allocate new p4d/pud pages + * that need to be propagated to all tasks' PGDs. + */ + sync_global_pgds(VMALLOC_START & PGDIR_MASK, VMALLOC_END); +} + +void vmalloc_sync_unmappings(void) +{ + /* + * Unmappings never allocate or free p4d/pud pages. + * No work is required here. + */ +} + +/* + * 64-bit: + * + * Handle a fault on the vmalloc area + */ +static noinline int vmalloc_fault(unsigned long address) +{ + pgd_t *pgd, *pgd_k; + p4d_t *p4d, *p4d_k; + pud_t *pud; + pmd_t *pmd; + pte_t *pte; + + /* Make sure we are in vmalloc area: */ + if (!(address >= VMALLOC_START && address < VMALLOC_END)) + return -1; + + /* + * Copy kernel mappings over when needed. This can also + * happen within a race in page table update. In the later + * case just flush: + */ + pgd = (pgd_t *)__va(read_cr3_pa()) + pgd_index(address); + pgd_k = pgd_offset_k(address); + if (pgd_none(*pgd_k)) + return -1; + + if (pgtable_l5_enabled()) { + if (pgd_none(*pgd)) { + set_pgd(pgd, *pgd_k); + arch_flush_lazy_mmu_mode(); + } else { + BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_k)); + } + } + + /* With 4-level paging, copying happens on the p4d level. */ + p4d = p4d_offset(pgd, address); + p4d_k = p4d_offset(pgd_k, address); + if (p4d_none(*p4d_k)) + return -1; + + if (p4d_none(*p4d) && !pgtable_l5_enabled()) { + set_p4d(p4d, *p4d_k); + arch_flush_lazy_mmu_mode(); + } else { + BUG_ON(p4d_pfn(*p4d) != p4d_pfn(*p4d_k)); + } + + BUILD_BUG_ON(CONFIG_PGTABLE_LEVELS < 4); + + pud = pud_offset(p4d, address); + if (pud_none(*pud)) + return -1; + + if (pud_large(*pud)) + return 0; + + pmd = pmd_offset(pud, address); + if (pmd_none(*pmd)) + return -1; + + if (pmd_large(*pmd)) + return 0; + + pte = pte_offset_kernel(pmd, address); + if (!pte_present(*pte)) + return -1; + + return 0; +} +NOKPROBE_SYMBOL(vmalloc_fault); + +#ifdef CONFIG_CPU_SUP_AMD +static const char errata93_warning[] = +KERN_ERR +"******* Your BIOS seems to not contain a fix for K8 errata #93\n" +"******* Working around it, but it may cause SEGVs or burn power.\n" +"******* Please consider a BIOS update.\n" +"******* Disabling USB legacy in the BIOS may also help.\n"; +#endif + +/* + * No vm86 mode in 64-bit mode: + */ +static inline void +check_v8086_mode(struct pt_regs *regs, unsigned long address, + struct task_struct *tsk) +{ +} + +static int bad_address(void *p) +{ + unsigned long dummy; + + return probe_kernel_address((unsigned long *)p, dummy); +} + +static void dump_pagetable(unsigned long address) +{ + pgd_t *base = __va(read_cr3_pa()); + pgd_t *pgd = base + pgd_index(address); + p4d_t *p4d; + pud_t *pud; + pmd_t *pmd; + pte_t *pte; + + if (bad_address(pgd)) + goto bad; + + pr_info("PGD %lx ", pgd_val(*pgd)); + + if (!pgd_present(*pgd)) + goto out; + + p4d = p4d_offset(pgd, address); + if (bad_address(p4d)) + goto bad; + + pr_cont("P4D %lx ", p4d_val(*p4d)); + if (!p4d_present(*p4d) || p4d_large(*p4d)) + goto out; + + pud = pud_offset(p4d, address); + if (bad_address(pud)) + goto bad; + + pr_cont("PUD %lx ", pud_val(*pud)); + if (!pud_present(*pud) || pud_large(*pud)) + goto out; + + pmd = pmd_offset(pud, address); + if (bad_address(pmd)) + goto bad; + + pr_cont("PMD %lx ", pmd_val(*pmd)); + if (!pmd_present(*pmd) || pmd_large(*pmd)) + goto out; + + pte = pte_offset_kernel(pmd, address); + if (bad_address(pte)) + goto bad; + + pr_cont("PTE %lx", pte_val(*pte)); +out: + pr_cont("\n"); + return; +bad: + pr_info("BAD\n"); +} + +#endif /* CONFIG_X86_64 */ + +/* + * Workaround for K8 erratum #93 & buggy BIOS. + * + * BIOS SMM functions are required to use a specific workaround + * to avoid corruption of the 64bit RIP register on C stepping K8. + * + * A lot of BIOS that didn't get tested properly miss this. + * + * The OS sees this as a page fault with the upper 32bits of RIP cleared. + * Try to work around it here. + * + * Note we only handle faults in kernel here. + * Does nothing on 32-bit. + */ +static int is_errata93(struct pt_regs *regs, unsigned long address) +{ +#if defined(CONFIG_X86_64) && defined(CONFIG_CPU_SUP_AMD) + if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD + || boot_cpu_data.x86 != 0xf) + return 0; + + if (address != regs->ip) + return 0; + + if ((address >> 32) != 0) + return 0; + + address |= 0xffffffffUL << 32; + if ((address >= (u64)_stext && address <= (u64)_etext) || + (address >= MODULES_VADDR && address <= MODULES_END)) { + printk_once(errata93_warning); + regs->ip = address; + return 1; + } +#endif + return 0; +} + +/* + * Work around K8 erratum #100 K8 in compat mode occasionally jumps + * to illegal addresses >4GB. + * + * We catch this in the page fault handler because these addresses + * are not reachable. Just detect this case and return. Any code + * segment in LDT is compatibility mode. + */ +static int is_errata100(struct pt_regs *regs, unsigned long address) +{ +#ifdef CONFIG_X86_64 + if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) && (address >> 32)) + return 1; +#endif + return 0; +} + +static int is_f00f_bug(struct pt_regs *regs, unsigned long address) +{ +#ifdef CONFIG_X86_F00F_BUG + unsigned long nr; + + /* + * Pentium F0 0F C7 C8 bug workaround: + */ + if (boot_cpu_has_bug(X86_BUG_F00F)) { + nr = (address - idt_descr.address) >> 3; + + if (nr == 6) { + do_invalid_op(regs, 0); + return 1; + } + } +#endif + return 0; +} + +static void +show_fault_oops(struct pt_regs *regs, unsigned long error_code, + unsigned long address) +{ + if (!oops_may_print()) + return; + + if (error_code & X86_PF_INSTR) { + unsigned int level; + pgd_t *pgd; + pte_t *pte; + + pgd = __va(read_cr3_pa()); + pgd += pgd_index(address); + + pte = lookup_address_in_pgd(pgd, address, &level); + + if (pte && pte_present(*pte) && !pte_exec(*pte)) + pr_crit("kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n", + from_kuid(&init_user_ns, current_uid())); + if (pte && pte_present(*pte) && pte_exec(*pte) && + (pgd_flags(*pgd) & _PAGE_USER) && + (__read_cr4() & X86_CR4_SMEP)) + pr_crit("unable to execute userspace code (SMEP?) (uid: %d)\n", + from_kuid(&init_user_ns, current_uid())); + } + + pr_alert("BUG: unable to handle kernel %s at %px\n", + address < PAGE_SIZE ? "NULL pointer dereference" : "paging request", + (void *)address); + + dump_pagetable(address); +} + +static noinline void +pgtable_bad(struct pt_regs *regs, unsigned long error_code, + unsigned long address) +{ + struct task_struct *tsk; + unsigned long flags; + int sig; + + flags = oops_begin(); + tsk = current; + sig = SIGKILL; + + printk(KERN_ALERT "%s: Corrupted page table at address %lx\n", + tsk->comm, address); + dump_pagetable(address); + + tsk->thread.cr2 = address; + tsk->thread.trap_nr = X86_TRAP_PF; + tsk->thread.error_code = error_code; + + if (__die("Bad pagetable", regs, error_code)) + sig = 0; + + oops_end(flags, regs, sig); +} + +static noinline void +no_context(struct pt_regs *regs, unsigned long error_code, + unsigned long address, int signal, int si_code) +{ + struct task_struct *tsk = current; + unsigned long flags; + int sig; + + /* Are we prepared to handle this kernel fault? */ + if (fixup_exception(regs, X86_TRAP_PF)) { + /* + * Any interrupt that takes a fault gets the fixup. This makes + * the below recursive fault logic only apply to a faults from + * task context. + */ + if (in_interrupt()) + return; + + /* + * Per the above we're !in_interrupt(), aka. task context. + * + * In this case we need to make sure we're not recursively + * faulting through the emulate_vsyscall() logic. + */ + if (current->thread.sig_on_uaccess_err && signal) { + tsk->thread.trap_nr = X86_TRAP_PF; + tsk->thread.error_code = error_code | X86_PF_USER; + tsk->thread.cr2 = address; + + /* XXX: hwpoison faults will set the wrong code. */ + force_sig_info_fault(signal, si_code, address, + tsk, NULL, 0); + } + + /* + * Barring that, we can do the fixup and be happy. + */ + return; + } + +#ifdef CONFIG_VMAP_STACK + /* + * Stack overflow? During boot, we can fault near the initial + * stack in the direct map, but that's not an overflow -- check + * that we're in vmalloc space to avoid this. + */ + if (is_vmalloc_addr((void *)address) && + (((unsigned long)tsk->stack - 1 - address < PAGE_SIZE) || + address - ((unsigned long)tsk->stack + THREAD_SIZE) < PAGE_SIZE)) { + unsigned long stack = this_cpu_read(orig_ist.ist[DOUBLEFAULT_STACK]) - sizeof(void *); + /* + * We're likely to be running with very little stack space + * left. It's plausible that we'd hit this condition but + * double-fault even before we get this far, in which case + * we're fine: the double-fault handler will deal with it. + * + * We don't want to make it all the way into the oops code + * and then double-fault, though, because we're likely to + * break the console driver and lose most of the stack dump. + */ + asm volatile ("movq %[stack], %%rsp\n\t" + "call handle_stack_overflow\n\t" + "1: jmp 1b" + : ASM_CALL_CONSTRAINT + : "D" ("kernel stack overflow (page fault)"), + "S" (regs), "d" (address), + [stack] "rm" (stack)); + unreachable(); + } +#endif + + /* + * 32-bit: + * + * Valid to do another page fault here, because if this fault + * had been triggered by is_prefetch fixup_exception would have + * handled it. + * + * 64-bit: + * + * Hall of shame of CPU/BIOS bugs. + */ + if (is_prefetch(regs, error_code, address)) + return; + + if (is_errata93(regs, address)) + return; + + /* + * Oops. The kernel tried to access some bad page. We'll have to + * terminate things with extreme prejudice: + */ + flags = oops_begin(); + + show_fault_oops(regs, error_code, address); + + if (task_stack_end_corrupted(tsk)) + printk(KERN_EMERG "Thread overran stack, or stack corrupted\n"); + + tsk->thread.cr2 = address; + tsk->thread.trap_nr = X86_TRAP_PF; + tsk->thread.error_code = error_code; + + sig = SIGKILL; + if (__die("Oops", regs, error_code)) + sig = 0; + + /* Executive summary in case the body of the oops scrolled away */ + printk(KERN_DEFAULT "CR2: %016lx\n", address); + + oops_end(flags, regs, sig); +} + +/* + * Print out info about fatal segfaults, if the show_unhandled_signals + * sysctl is set: + */ +static inline void +show_signal_msg(struct pt_regs *regs, unsigned long error_code, + unsigned long address, struct task_struct *tsk) +{ + const char *loglvl = task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG; + + if (!unhandled_signal(tsk, SIGSEGV)) + return; + + if (!printk_ratelimit()) + return; + + printk("%s%s[%d]: segfault at %lx ip %px sp %px error %lx", + loglvl, tsk->comm, task_pid_nr(tsk), address, + (void *)regs->ip, (void *)regs->sp, error_code); + + print_vma_addr(KERN_CONT " in ", regs->ip); + + printk(KERN_CONT "\n"); + + show_opcodes(regs, loglvl); +} + +static void +__bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code, + unsigned long address, u32 *pkey, int si_code) +{ + struct task_struct *tsk = current; + + /* User mode accesses just cause a SIGSEGV */ + if (error_code & X86_PF_USER) { + /* + * It's possible to have interrupts off here: + */ + local_irq_enable(); + + /* + * Valid to do another page fault here because this one came + * from user space: + */ + if (is_prefetch(regs, error_code, address)) + return; + + if (is_errata100(regs, address)) + return; + +#ifdef CONFIG_X86_64 + /* + * Instruction fetch faults in the vsyscall page might need + * emulation. + */ + if (unlikely((error_code & X86_PF_INSTR) && + ((address & ~0xfff) == VSYSCALL_ADDR))) { + if (emulate_vsyscall(regs, address)) + return; + } +#endif + + /* + * To avoid leaking information about the kernel page table + * layout, pretend that user-mode accesses to kernel addresses + * are always protection faults. + */ + if (address >= TASK_SIZE_MAX) + error_code |= X86_PF_PROT; + + if (likely(show_unhandled_signals)) + show_signal_msg(regs, error_code, address, tsk); + + tsk->thread.cr2 = address; + tsk->thread.error_code = error_code; + tsk->thread.trap_nr = X86_TRAP_PF; + + force_sig_info_fault(SIGSEGV, si_code, address, tsk, pkey, 0); + + return; + } + + if (is_f00f_bug(regs, address)) + return; + + no_context(regs, error_code, address, SIGSEGV, si_code); +} + +static noinline void +bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code, + unsigned long address, u32 *pkey) +{ + __bad_area_nosemaphore(regs, error_code, address, pkey, SEGV_MAPERR); +} + +static void +__bad_area(struct pt_regs *regs, unsigned long error_code, + unsigned long address, struct vm_area_struct *vma, int si_code) +{ + struct mm_struct *mm = current->mm; + u32 pkey; + + if (vma) + pkey = vma_pkey(vma); + + /* + * Something tried to access memory that isn't in our memory map.. + * Fix it, but check if it's kernel or user first.. + */ + up_read(&mm->mmap_sem); + + __bad_area_nosemaphore(regs, error_code, address, + (vma) ? &pkey : NULL, si_code); +} + +static noinline void +bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address) +{ + __bad_area(regs, error_code, address, NULL, SEGV_MAPERR); +} + +static inline bool bad_area_access_from_pkeys(unsigned long error_code, + struct vm_area_struct *vma) +{ + /* This code is always called on the current mm */ + bool foreign = false; + + if (!boot_cpu_has(X86_FEATURE_OSPKE)) + return false; + if (error_code & X86_PF_PK) + return true; + /* this checks permission keys on the VMA: */ + if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE), + (error_code & X86_PF_INSTR), foreign)) + return true; + return false; +} + +static noinline void +bad_area_access_error(struct pt_regs *regs, unsigned long error_code, + unsigned long address, struct vm_area_struct *vma) +{ + /* + * This OSPKE check is not strictly necessary at runtime. + * But, doing it this way allows compiler optimizations + * if pkeys are compiled out. + */ + if (bad_area_access_from_pkeys(error_code, vma)) + __bad_area(regs, error_code, address, vma, SEGV_PKUERR); + else + __bad_area(regs, error_code, address, vma, SEGV_ACCERR); +} + +static void +do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address, + u32 *pkey, unsigned int fault) +{ + struct task_struct *tsk = current; + int code = BUS_ADRERR; + + /* Kernel mode? Handle exceptions or die: */ + if (!(error_code & X86_PF_USER)) { + no_context(regs, error_code, address, SIGBUS, BUS_ADRERR); + return; + } + + /* User-space => ok to do another page fault: */ + if (is_prefetch(regs, error_code, address)) + return; + + tsk->thread.cr2 = address; + tsk->thread.error_code = error_code; + tsk->thread.trap_nr = X86_TRAP_PF; + +#ifdef CONFIG_MEMORY_FAILURE + if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) { + printk(KERN_ERR + "MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n", + tsk->comm, tsk->pid, address); + code = BUS_MCEERR_AR; + } +#endif + force_sig_info_fault(SIGBUS, code, address, tsk, pkey, fault); +} + +static noinline void +mm_fault_error(struct pt_regs *regs, unsigned long error_code, + unsigned long address, u32 *pkey, vm_fault_t fault) +{ + if (fatal_signal_pending(current) && !(error_code & X86_PF_USER)) { + no_context(regs, error_code, address, 0, 0); + return; + } + + if (fault & VM_FAULT_OOM) { + /* Kernel mode? Handle exceptions or die: */ + if (!(error_code & X86_PF_USER)) { + no_context(regs, error_code, address, + SIGSEGV, SEGV_MAPERR); + return; + } + + /* + * We ran out of memory, call the OOM killer, and return the + * userspace (which will retry the fault, or kill us if we got + * oom-killed): + */ + pagefault_out_of_memory(); + } else { + if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON| + VM_FAULT_HWPOISON_LARGE)) + do_sigbus(regs, error_code, address, pkey, fault); + else if (fault & VM_FAULT_SIGSEGV) + bad_area_nosemaphore(regs, error_code, address, pkey); + else + BUG(); + } +} + +static int spurious_fault_check(unsigned long error_code, pte_t *pte) +{ + if ((error_code & X86_PF_WRITE) && !pte_write(*pte)) + return 0; + + if ((error_code & X86_PF_INSTR) && !pte_exec(*pte)) + return 0; + /* + * Note: We do not do lazy flushing on protection key + * changes, so no spurious fault will ever set X86_PF_PK. + */ + if ((error_code & X86_PF_PK)) + return 1; + + return 1; +} + +/* + * Handle a spurious fault caused by a stale TLB entry. + * + * This allows us to lazily refresh the TLB when increasing the + * permissions of a kernel page (RO -> RW or NX -> X). Doing it + * eagerly is very expensive since that implies doing a full + * cross-processor TLB flush, even if no stale TLB entries exist + * on other processors. + * + * Spurious faults may only occur if the TLB contains an entry with + * fewer permission than the page table entry. Non-present (P = 0) + * and reserved bit (R = 1) faults are never spurious. + * + * There are no security implications to leaving a stale TLB when + * increasing the permissions on a page. + * + * Returns non-zero if a spurious fault was handled, zero otherwise. + * + * See Intel Developer's Manual Vol 3 Section 4.10.4.3, bullet 3 + * (Optional Invalidation). + */ +static noinline int +spurious_fault(unsigned long error_code, unsigned long address) +{ + pgd_t *pgd; + p4d_t *p4d; + pud_t *pud; + pmd_t *pmd; + pte_t *pte; + int ret; + + /* + * Only writes to RO or instruction fetches from NX may cause + * spurious faults. + * + * These could be from user or supervisor accesses but the TLB + * is only lazily flushed after a kernel mapping protection + * change, so user accesses are not expected to cause spurious + * faults. + */ + if (error_code != (X86_PF_WRITE | X86_PF_PROT) && + error_code != (X86_PF_INSTR | X86_PF_PROT)) + return 0; + + pgd = init_mm.pgd + pgd_index(address); + if (!pgd_present(*pgd)) + return 0; + + p4d = p4d_offset(pgd, address); + if (!p4d_present(*p4d)) + return 0; + + if (p4d_large(*p4d)) + return spurious_fault_check(error_code, (pte_t *) p4d); + + pud = pud_offset(p4d, address); + if (!pud_present(*pud)) + return 0; + + if (pud_large(*pud)) + return spurious_fault_check(error_code, (pte_t *) pud); + + pmd = pmd_offset(pud, address); + if (!pmd_present(*pmd)) + return 0; + + if (pmd_large(*pmd)) + return spurious_fault_check(error_code, (pte_t *) pmd); + + pte = pte_offset_kernel(pmd, address); + if (!pte_present(*pte)) + return 0; + + ret = spurious_fault_check(error_code, pte); + if (!ret) + return 0; + + /* + * Make sure we have permissions in PMD. + * If not, then there's a bug in the page tables: + */ + ret = spurious_fault_check(error_code, (pte_t *) pmd); + WARN_ONCE(!ret, "PMD has incorrect permission bits\n"); + + return ret; +} +NOKPROBE_SYMBOL(spurious_fault); + +int show_unhandled_signals = 1; + +static inline int +access_error(unsigned long error_code, struct vm_area_struct *vma) +{ + /* This is only called for the current mm, so: */ + bool foreign = false; + + /* + * Read or write was blocked by protection keys. This is + * always an unconditional error and can never result in + * a follow-up action to resolve the fault, like a COW. + */ + if (error_code & X86_PF_PK) + return 1; + + /* + * Make sure to check the VMA so that we do not perform + * faults just to hit a X86_PF_PK as soon as we fill in a + * page. + */ + if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE), + (error_code & X86_PF_INSTR), foreign)) + return 1; + + if (error_code & X86_PF_WRITE) { + /* write, present and write, not present: */ + if (unlikely(!(vma->vm_flags & VM_WRITE))) + return 1; + return 0; + } + + /* read, present: */ + if (unlikely(error_code & X86_PF_PROT)) + return 1; + + /* read, not present: */ + if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))) + return 1; + + return 0; +} + +static int fault_in_kernel_space(unsigned long address) +{ + return address >= TASK_SIZE_MAX; +} + +static inline bool smap_violation(int error_code, struct pt_regs *regs) +{ + if (!IS_ENABLED(CONFIG_X86_SMAP)) + return false; + + if (!static_cpu_has(X86_FEATURE_SMAP)) + return false; + + if (error_code & X86_PF_USER) + return false; + + if (!user_mode(regs) && (regs->flags & X86_EFLAGS_AC)) + return false; + + return true; +} + +/* + * This routine handles page faults. It determines the address, + * and the problem, and then passes it off to one of the appropriate + * routines. + */ +static noinline void +__do_page_fault(struct pt_regs *regs, unsigned long error_code, + unsigned long address) +{ + struct vm_area_struct *vma; + struct task_struct *tsk; + struct mm_struct *mm; + vm_fault_t fault, major = 0; + unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE; + u32 pkey; + + tsk = current; + mm = tsk->mm; + + prefetchw(&mm->mmap_sem); + + if (unlikely(kmmio_fault(regs, address))) + return; + + /* + * We fault-in kernel-space virtual memory on-demand. The + * 'reference' page table is init_mm.pgd. + * + * NOTE! We MUST NOT take any locks for this case. We may + * be in an interrupt or a critical region, and should + * only copy the information from the master page table, + * nothing more. + * + * This verifies that the fault happens in kernel space + * (error_code & 4) == 0, and that the fault was not a + * protection error (error_code & 9) == 0. + */ + if (unlikely(fault_in_kernel_space(address))) { + if (!(error_code & (X86_PF_RSVD | X86_PF_USER | X86_PF_PROT))) { + if (vmalloc_fault(address) >= 0) + return; + } + + /* Can handle a stale RO->RW TLB: */ + if (spurious_fault(error_code, address)) + return; + + /* kprobes don't want to hook the spurious faults: */ + if (kprobes_fault(regs)) + return; + /* + * Don't take the mm semaphore here. If we fixup a prefetch + * fault we could otherwise deadlock: + */ + bad_area_nosemaphore(regs, error_code, address, NULL); + + return; + } + + /* kprobes don't want to hook the spurious faults: */ + if (unlikely(kprobes_fault(regs))) + return; + + if (unlikely(error_code & X86_PF_RSVD)) + pgtable_bad(regs, error_code, address); + + if (unlikely(smap_violation(error_code, regs))) { + bad_area_nosemaphore(regs, error_code, address, NULL); + return; + } + + /* + * If we're in an interrupt, have no user context or are running + * in a region with pagefaults disabled then we must not take the fault + */ + if (unlikely(faulthandler_disabled() || !mm)) { + bad_area_nosemaphore(regs, error_code, address, NULL); + return; + } + + /* + * It's safe to allow irq's after cr2 has been saved and the + * vmalloc fault has been handled. + * + * User-mode registers count as a user access even for any + * potential system fault or CPU buglet: + */ + if (user_mode(regs)) { + local_irq_enable(); + error_code |= X86_PF_USER; + flags |= FAULT_FLAG_USER; + } else { + if (regs->flags & X86_EFLAGS_IF) + local_irq_enable(); + } + + perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address); + + if (error_code & X86_PF_WRITE) + flags |= FAULT_FLAG_WRITE; + if (error_code & X86_PF_INSTR) + flags |= FAULT_FLAG_INSTRUCTION; + + /* + * When running in the kernel we expect faults to occur only to + * addresses in user space. All other faults represent errors in + * the kernel and should generate an OOPS. Unfortunately, in the + * case of an erroneous fault occurring in a code path which already + * holds mmap_sem we will deadlock attempting to validate the fault + * against the address space. Luckily the kernel only validly + * references user space from well defined areas of code, which are + * listed in the exceptions table. + * + * As the vast majority of faults will be valid we will only perform + * the source reference check when there is a possibility of a + * deadlock. Attempt to lock the address space, if we cannot we then + * validate the source. If this is invalid we can skip the address + * space check, thus avoiding the deadlock: + */ + if (unlikely(!down_read_trylock(&mm->mmap_sem))) { + if (!(error_code & X86_PF_USER) && + !search_exception_tables(regs->ip)) { + bad_area_nosemaphore(regs, error_code, address, NULL); + return; + } +retry: + down_read(&mm->mmap_sem); + } else { + /* + * The above down_read_trylock() might have succeeded in + * which case we'll have missed the might_sleep() from + * down_read(): + */ + might_sleep(); + } + + vma = find_vma(mm, address); + if (unlikely(!vma)) { + bad_area(regs, error_code, address); + return; + } + if (likely(vma->vm_start <= address)) + goto good_area; + if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) { + bad_area(regs, error_code, address); + return; + } + if (error_code & X86_PF_USER) { + /* + * Accessing the stack below %sp is always a bug. + * The large cushion allows instructions like enter + * and pusha to work. ("enter $65535, $31" pushes + * 32 pointers and then decrements %sp by 65535.) + */ + if (unlikely(address + 65536 + 32 * sizeof(unsigned long) < regs->sp)) { + bad_area(regs, error_code, address); + return; + } + } + if (unlikely(expand_stack(vma, address))) { + bad_area(regs, error_code, address); + return; + } + + /* + * Ok, we have a good vm_area for this memory access, so + * we can handle it.. + */ +good_area: + if (unlikely(access_error(error_code, vma))) { + bad_area_access_error(regs, error_code, address, vma); + return; + } + + /* + * If for any reason at all we couldn't handle the fault, + * make sure we exit gracefully rather than endlessly redo + * the fault. Since we never set FAULT_FLAG_RETRY_NOWAIT, if + * we get VM_FAULT_RETRY back, the mmap_sem has been unlocked. + * + * Note that handle_userfault() may also release and reacquire mmap_sem + * (and not return with VM_FAULT_RETRY), when returning to userland to + * repeat the page fault later with a VM_FAULT_NOPAGE retval + * (potentially after handling any pending signal during the return to + * userland). The return to userland is identified whenever + * FAULT_FLAG_USER|FAULT_FLAG_KILLABLE are both set in flags. + * Thus we have to be careful about not touching vma after handling the + * fault, so we read the pkey beforehand. + */ + pkey = vma_pkey(vma); + fault = handle_mm_fault(vma, address, flags); + major |= fault & VM_FAULT_MAJOR; + + /* + * If we need to retry the mmap_sem has already been released, + * and if there is a fatal signal pending there is no guarantee + * that we made any progress. Handle this case first. + */ + if (unlikely(fault & VM_FAULT_RETRY)) { + /* Retry at most once */ + if (flags & FAULT_FLAG_ALLOW_RETRY) { + flags &= ~FAULT_FLAG_ALLOW_RETRY; + flags |= FAULT_FLAG_TRIED; + if (!fatal_signal_pending(tsk)) + goto retry; + } + + /* User mode? Just return to handle the fatal exception */ + if (flags & FAULT_FLAG_USER) + return; + + /* Not returning to user mode? Handle exceptions or die: */ + no_context(regs, error_code, address, SIGBUS, BUS_ADRERR); + return; + } + + up_read(&mm->mmap_sem); + if (unlikely(fault & VM_FAULT_ERROR)) { + mm_fault_error(regs, error_code, address, &pkey, fault); + return; + } + + /* + * Major/minor page fault accounting. If any of the events + * returned VM_FAULT_MAJOR, we account it as a major fault. + */ + if (major) { + tsk->maj_flt++; + perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, regs, address); + } else { + tsk->min_flt++; + perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs, address); + } + + check_v8086_mode(regs, address, tsk); +} +NOKPROBE_SYMBOL(__do_page_fault); + +static nokprobe_inline void +trace_page_fault_entries(unsigned long address, struct pt_regs *regs, + unsigned long error_code) +{ + if (user_mode(regs)) + trace_page_fault_user(address, regs, error_code); + else + trace_page_fault_kernel(address, regs, error_code); +} + +/* + * We must have this function blacklisted from kprobes, tagged with notrace + * and call read_cr2() before calling anything else. To avoid calling any + * kind of tracing machinery before we've observed the CR2 value. + * + * exception_{enter,exit}() contains all sorts of tracepoints. + */ +dotraplinkage void notrace +do_page_fault(struct pt_regs *regs, unsigned long error_code) +{ + unsigned long address = read_cr2(); /* Get the faulting address */ + enum ctx_state prev_state; + + prev_state = exception_enter(); + if (trace_pagefault_enabled()) + trace_page_fault_entries(address, regs, error_code); + + __do_page_fault(regs, error_code, address); + exception_exit(prev_state); +} +NOKPROBE_SYMBOL(do_page_fault); |