fault.c

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/*
 * Based on arch/arm/mm/fault.c
 *
 * Copyright (C) 1995  Linus Torvalds
 * Copyright (C) 1995-2004 Russell King
 * Copyright (C) 2012 ARM Ltd.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <linux/module.h>
#include <linux/signal.h>
#include <linux/mm.h>
#include <linux/hardirq.h>
#include <linux/init.h>
#include <linux/kprobes.h>
#include <linux/uaccess.h>
#include <linux/page-flags.h>
#include <linux/sched.h>
#include <linux/highmem.h>
#include <linux/perf_event.h>

#include <asm/exception.h>
#include <asm/debug-monitors.h>
#include <asm/system_misc.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>

/*
 * Dump out the page tables associated with 'addr' in mm 'mm'.
 */
void show_pte(struct mm_struct *mm, unsigned long addr)
{
    pgd_t *pgd;

    if (!mm)
        mm = &init_mm;

    pr_alert("pgd = %p\n", mm->pgd);
    pgd = pgd_offset(mm, addr);
    pr_alert("[%08lx] *pgd=%016llx", addr, pgd_val(*pgd));

    do {
        pud_t *pud;
        pmd_t *pmd;
        pte_t *pte;

        if (pgd_none_or_clear_bad(pgd))
            break;

        pud = pud_offset(pgd, addr);
        if (pud_none_or_clear_bad(pud))
            break;

        pmd = pmd_offset(pud, addr);
        printk(", *pmd=%016llx", pmd_val(*pmd));
        if (pmd_none_or_clear_bad(pmd))
            break;

        pte = pte_offset_map(pmd, addr);
        printk(", *pte=%016llx", pte_val(*pte));
        pte_unmap(pte);
    } while(0);

    printk("\n");
}

/*
 * The kernel tried to access some page that wasn't present.
 */
static void __do_kernel_fault(struct mm_struct *mm, unsigned long addr,
                  unsigned int esr, struct pt_regs *regs)
{
    /*
     * Are we prepared to handle this kernel fault?
     */
    if (fixup_exception(regs))
        return;

    /*
     * No handler, we'll have to terminate things with extreme prejudice.
     */
    bust_spinlocks(1);
    pr_alert("Unable to handle kernel %s at virtual address %08lx\n",
         (addr < PAGE_SIZE) ? "NULL pointer dereference" :
         "paging request", addr);

    show_pte(mm, addr);
    die("Oops", regs, esr);
    bust_spinlocks(0);
    do_exit(SIGKILL);
}

/*
 * Something tried to access memory that isn't in our memory map. User mode
 * accesses just cause a SIGSEGV
 */
static void __do_user_fault(struct task_struct *tsk, unsigned long addr,
                unsigned int esr, unsigned int sig, int code,
                struct pt_regs *regs)
{
    struct siginfo si;

    if (show_unhandled_signals) {
        pr_info("%s[%d]: unhandled page fault (%d) at 0x%08lx, code 0x%03x\n",
            tsk->comm, task_pid_nr(tsk), sig, addr, esr);
        show_pte(tsk->mm, addr);
        show_regs(regs);
    }

    tsk->thread.fault_address = addr;
    si.si_signo = sig;
    si.si_errno = 0;
    si.si_code = code;
    si.si_addr = (void __user *)addr;
    force_sig_info(sig, &si, tsk);
}

void do_bad_area(unsigned long addr, unsigned int esr, struct pt_regs *regs)
{
    struct task_struct *tsk = current;
    struct mm_struct *mm = tsk->active_mm;

    /*
     * If we are in kernel mode at this point, we have no context to
     * handle this fault with.
     */
    if (user_mode(regs))
        __do_user_fault(tsk, addr, esr, SIGSEGV, SEGV_MAPERR, regs);
    else
        __do_kernel_fault(mm, addr, esr, regs);
}

#define VM_FAULT_BADMAP     0x010000
#define VM_FAULT_BADACCESS  0x020000

#define ESR_WRITE       (1 << 6)
#define ESR_LNX_EXEC        (1 << 24)

/*
 * Check that the permissions on the VMA allow for the fault which occurred.
 * If we encountered a write fault, we must have write permission, otherwise
 * we allow any permission.
 */
static inline bool access_error(unsigned int esr, struct vm_area_struct *vma)
{
    unsigned int mask = VM_READ | VM_WRITE | VM_EXEC;

    if (esr & ESR_WRITE)
        mask = VM_WRITE;
    if (esr & ESR_LNX_EXEC)
        mask = VM_EXEC;

    return vma->vm_flags & mask ? false : true;
}

static int __do_page_fault(struct mm_struct *mm, unsigned long addr,
               unsigned int esr, unsigned int flags,
               struct task_struct *tsk)
{
    struct vm_area_struct *vma;
    int fault;

    vma = find_vma(mm, addr);
    fault = VM_FAULT_BADMAP;
    if (unlikely(!vma))
        goto out;
    if (unlikely(vma->vm_start > addr))
        goto check_stack;

    /*
     * Ok, we have a good vm_area for this memory access, so we can handle
     * it.
     */
good_area:
    if (access_error(esr, vma)) {
        fault = VM_FAULT_BADACCESS;
        goto out;
    }

    return handle_mm_fault(mm, vma, addr & PAGE_MASK, flags);

check_stack:
    if (vma->vm_flags & VM_GROWSDOWN && !expand_stack(vma, addr))
        goto good_area;
out:
    return fault;
}

static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
                   struct pt_regs *regs)
{
    struct task_struct *tsk;
    struct mm_struct *mm;
    int fault, sig, code;
    int write = esr & ESR_WRITE;
    unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE |
        (write ? FAULT_FLAG_WRITE : 0);

    tsk = current;
    mm  = tsk->mm;

    /* Enable interrupts if they were enabled in the parent context. */
    if (interrupts_enabled(regs))
        local_irq_enable();

    /*
     * If we're in an interrupt or have no user context, we must not take
     * the fault.
     */
    if (in_atomic() || !mm)
        goto no_context;

    /*
     * As per x86, we may deadlock here. However, since the kernel only
     * validly references user space from well defined areas of the code,
     * we can bug out early if this is from code which shouldn't.
     */
    if (!down_read_trylock(&mm->mmap_sem)) {
        if (!user_mode(regs) && !search_exception_tables(regs->pc))
            goto no_context;
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();
#ifdef CONFIG_DEBUG_VM
        if (!user_mode(regs) && !search_exception_tables(regs->pc))
            goto no_context;
#endif
    }

    fault = __do_page_fault(mm, addr, esr, flags, tsk);

    /*
     * If we need to retry but a fatal signal is pending, handle the
     * signal first. We do not need to release the mmap_sem because it
     * would already be released in __lock_page_or_retry in mm/filemap.c.
     */
    if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
        return 0;

    /*
     * Major/minor page fault accounting is only done on the initial
     * attempt. If we go through a retry, it is extremely likely that the
     * page will be found in page cache at that point.
     */

    perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
    if (flags & FAULT_FLAG_ALLOW_RETRY) {
        if (fault & VM_FAULT_MAJOR) {
            tsk->maj_flt++;
            perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, regs,
                      addr);
        } else {
            tsk->min_flt++;
            perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs,
                      addr);
        }
        if (fault & VM_FAULT_RETRY) {
            /*
             * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk of
             * starvation.
             */
            flags &= ~FAULT_FLAG_ALLOW_RETRY;
            goto retry;
        }
    }

    up_read(&mm->mmap_sem);

    /*
     * Handle the "normal" case first - VM_FAULT_MAJOR / VM_FAULT_MINOR
     */
    if (likely(!(fault & (VM_FAULT_ERROR | VM_FAULT_BADMAP |
                  VM_FAULT_BADACCESS))))
        return 0;

    if (fault & VM_FAULT_OOM) {
        /*
         * We ran out of memory, call the OOM killer, and return to
         * userspace (which will retry the fault, or kill us if we got
         * oom-killed).
         */
        pagefault_out_of_memory();
        return 0;
    }

    /*
     * If we are in kernel mode at this point, we have no context to
     * handle this fault with.
     */
    if (!user_mode(regs))
        goto no_context;

    if (fault & VM_FAULT_SIGBUS) {
        /*
         * We had some memory, but were unable to successfully fix up
         * this page fault.
         */
        sig = SIGBUS;
        code = BUS_ADRERR;
    } else {
        /*
         * Something tried to access memory that isn't in our memory
         * map.
         */
        sig = SIGSEGV;
        code = fault == VM_FAULT_BADACCESS ?
            SEGV_ACCERR : SEGV_MAPERR;
    }

    __do_user_fault(tsk, addr, esr, sig, code, regs);
    return 0;

no_context:
    __do_kernel_fault(mm, addr, esr, regs);
    return 0;
}

/*
 * First Level Translation Fault Handler
 *
 * We enter here because the first level page table doesn't contain a valid
 * entry for the address.
 *
 * If the address is in kernel space (>= TASK_SIZE), then we are probably
 * faulting in the vmalloc() area.
 *
 * If the init_task's first level page tables contains the relevant entry, we
 * copy the it to this task.  If not, we send the process a signal, fixup the
 * exception, or oops the kernel.
 *
 * 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.
 */
static int __kprobes do_translation_fault(unsigned long addr,
                      unsigned int esr,
                      struct pt_regs *regs)
{
    if (addr < TASK_SIZE)
        return do_page_fault(addr, esr, regs);

    do_bad_area(addr, esr, regs);
    return 0;
}

/*
 * Some section permission faults need to be handled gracefully.  They can
 * happen due to a __{get,put}_user during an oops.
 */
static int do_sect_fault(unsigned long addr, unsigned int esr,
             struct pt_regs *regs)
{
    do_bad_area(addr, esr, regs);
    return 0;
}

/*
 * This abort handler always returns "fault".
 */
static int do_bad(unsigned long addr, unsigned int esr, struct pt_regs *regs)
{
    return 1;
}

static struct fault_info {
    int (*fn)(unsigned long addr, unsigned int esr, struct pt_regs *regs);
    int sig;
    int code;
    const char *name;
} fault_info[] = {
    { do_bad,       SIGBUS,  0,     "ttbr address size fault"   },
    { do_bad,       SIGBUS,  0,     "level 1 address size fault"    },
    { do_bad,       SIGBUS,  0,     "level 2 address size fault"    },
    { do_bad,       SIGBUS,  0,     "level 3 address size fault"    },
    { do_translation_fault, SIGSEGV, SEGV_MAPERR,   "input address range fault" },
    { do_translation_fault, SIGSEGV, SEGV_MAPERR,   "level 1 translation fault" },
    { do_translation_fault, SIGSEGV, SEGV_MAPERR,   "level 2 translation fault" },
    { do_page_fault,    SIGSEGV, SEGV_MAPERR,   "level 3 translation fault" },
    { do_bad,       SIGBUS,  0,     "reserved access flag fault"    },
    { do_bad,       SIGSEGV, SEGV_ACCERR,   "level 1 access flag fault" },
    { do_bad,       SIGSEGV, SEGV_ACCERR,   "level 2 access flag fault" },
    { do_page_fault,    SIGSEGV, SEGV_ACCERR,   "level 3 access flag fault" },
    { do_bad,       SIGBUS,  0,     "reserved permission fault" },
    { do_bad,       SIGSEGV, SEGV_ACCERR,   "level 1 permission fault"  },
    { do_sect_fault,    SIGSEGV, SEGV_ACCERR,   "level 2 permission fault"  },
    { do_page_fault,    SIGSEGV, SEGV_ACCERR,   "level 3 permission fault"  },
    { do_bad,       SIGBUS,  0,     "synchronous external abort"    },
    { do_bad,       SIGBUS,  0,     "asynchronous external abort"   },
    { do_bad,       SIGBUS,  0,     "unknown 18"            },
    { do_bad,       SIGBUS,  0,     "unknown 19"            },
    { do_bad,       SIGBUS,  0,     "synchronous abort (translation table walk)" },
    { do_bad,       SIGBUS,  0,     "synchronous abort (translation table walk)" },
    { do_bad,       SIGBUS,  0,     "synchronous abort (translation table walk)" },
    { do_bad,       SIGBUS,  0,     "synchronous abort (translation table walk)" },
    { do_bad,       SIGBUS,  0,     "synchronous parity error"  },
    { do_bad,       SIGBUS,  0,     "asynchronous parity error" },
    { do_bad,       SIGBUS,  0,     "unknown 26"            },
    { do_bad,       SIGBUS,  0,     "unknown 27"            },
    { do_bad,       SIGBUS,  0,     "synchronous parity error (translation table walk" },
    { do_bad,       SIGBUS,  0,     "synchronous parity error (translation table walk" },
    { do_bad,       SIGBUS,  0,     "synchronous parity error (translation table walk" },
    { do_bad,       SIGBUS,  0,     "synchronous parity error (translation table walk" },
    { do_bad,       SIGBUS,  0,     "unknown 32"            },
    { do_bad,       SIGBUS,  BUS_ADRALN,    "alignment fault"       },
    { do_bad,       SIGBUS,  0,     "debug event"           },
    { do_bad,       SIGBUS,  0,     "unknown 35"            },
    { do_bad,       SIGBUS,  0,     "unknown 36"            },
    { do_bad,       SIGBUS,  0,     "unknown 37"            },
    { do_bad,       SIGBUS,  0,     "unknown 38"            },
    { do_bad,       SIGBUS,  0,     "unknown 39"            },
    { do_bad,       SIGBUS,  0,     "unknown 40"            },
    { do_bad,       SIGBUS,  0,     "unknown 41"            },
    { do_bad,       SIGBUS,  0,     "unknown 42"            },
    { do_bad,       SIGBUS,  0,     "unknown 43"            },
    { do_bad,       SIGBUS,  0,     "unknown 44"            },
    { do_bad,       SIGBUS,  0,     "unknown 45"            },
    { do_bad,       SIGBUS,  0,     "unknown 46"            },
    { do_bad,       SIGBUS,  0,     "unknown 47"            },
    { do_bad,       SIGBUS,  0,     "unknown 48"            },
    { do_bad,       SIGBUS,  0,     "unknown 49"            },
    { do_bad,       SIGBUS,  0,     "unknown 50"            },
    { do_bad,       SIGBUS,  0,     "unknown 51"            },
    { do_bad,       SIGBUS,  0,     "implementation fault (lockdown abort)" },
    { do_bad,       SIGBUS,  0,     "unknown 53"            },
    { do_bad,       SIGBUS,  0,     "unknown 54"            },
    { do_bad,       SIGBUS,  0,     "unknown 55"            },
    { do_bad,       SIGBUS,  0,     "unknown 56"            },
    { do_bad,       SIGBUS,  0,     "unknown 57"            },
    { do_bad,       SIGBUS,  0,     "implementation fault (coprocessor abort)" },
    { do_bad,       SIGBUS,  0,     "unknown 59"            },
    { do_bad,       SIGBUS,  0,     "unknown 60"            },
    { do_bad,       SIGBUS,  0,     "unknown 61"            },
    { do_bad,       SIGBUS,  0,     "unknown 62"            },
    { do_bad,       SIGBUS,  0,     "unknown 63"            },
};

/*
 * Dispatch a data abort to the relevant handler.
 */
asmlinkage void __exception do_mem_abort(unsigned long addr, unsigned int esr,
                     struct pt_regs *regs)
{
    const struct fault_info *inf = fault_info + (esr & 63);
    struct siginfo info;

    if (!inf->fn(addr, esr, regs))
        return;

    pr_alert("Unhandled fault: %s (0x%08x) at 0x%016lx\n",
         inf->name, esr, addr);

    info.si_signo = inf->sig;
    info.si_errno = 0;
    info.si_code  = inf->code;
    info.si_addr  = (void __user *)addr;
    arm64_notify_die("", regs, &info, esr);
}

/*
 * Handle stack alignment exceptions.
 */
asmlinkage void __exception do_sp_pc_abort(unsigned long addr,
                       unsigned int esr,
                       struct pt_regs *regs)
{
    struct siginfo info;

    info.si_signo = SIGBUS;
    info.si_errno = 0;
    info.si_code  = BUS_ADRALN;
    info.si_addr  = (void __user *)addr;
    arm64_notify_die("", regs, &info, esr);
}

static struct fault_info debug_fault_info[] = {
    { do_bad,   SIGTRAP,    TRAP_HWBKPT,    "hardware breakpoint"   },
    { do_bad,   SIGTRAP,    TRAP_HWBKPT,    "hardware single-step"  },
    { do_bad,   SIGTRAP,    TRAP_HWBKPT,    "hardware watchpoint"   },
    { do_bad,   SIGBUS,     0,      "unknown 3"     },
    { do_bad,   SIGTRAP,    TRAP_BRKPT, "aarch32 BKPT"      },
    { do_bad,   SIGTRAP,    0,      "aarch32 vector catch"  },
    { do_bad,   SIGTRAP,    TRAP_BRKPT, "aarch64 BRK"       },
    { do_bad,   SIGBUS,     0,      "unknown 7"     },
};

void __init hook_debug_fault_code(int nr,
                  int (*fn)(unsigned long, unsigned int, struct pt_regs *),
                  int sig, int code, const char *name)
{
    BUG_ON(nr < 0 || nr >= ARRAY_SIZE(debug_fault_info));

    debug_fault_info[nr].fn     = fn;
    debug_fault_info[nr].sig    = sig;
    debug_fault_info[nr].code   = code;
    debug_fault_info[nr].name   = name;
}

asmlinkage int __exception do_debug_exception(unsigned long addr,
                          unsigned int esr,
                          struct pt_regs *regs)
{
    const struct fault_info *inf = debug_fault_info + DBG_ESR_EVT(esr);
    struct siginfo info;

    if (!inf->fn(addr, esr, regs))
        return 1;

    pr_alert("Unhandled debug exception: %s (0x%08x) at 0x%016lx\n",
         inf->name, esr, addr);

    info.si_signo = inf->sig;
    info.si_errno = 0;
    info.si_code  = inf->code;
    info.si_addr  = (void __user *)addr;
    arm64_notify_die("", regs, &info, esr);

    return 0;
}