/*
 *  PowerPC version
 *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
 *
 *  Derived from "arch/i386/mm/fault.c"
 *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *
 *  Modified by Cort Dougan and Paul Mackerras.
 *
 *  Modified for PPC64 by Dave Engebretsen (engebret@ibm.com)
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version
 *  2 of the License, or (at your option) any later version.
 */

#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/sched/task_stack.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/ptrace.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/highmem.h>
#include <linux/extable.h>
#include <linux/kprobes.h>
#include <linux/kdebug.h>
#include <linux/perf_event.h>
#include <linux/ratelimit.h>
#include <linux/context_tracking.h>
#include <linux/hugetlb.h>
#include <linux/uaccess.h>

#include <asm/firmware.h>
#include <asm/page.h>
#include <asm/pgtable.h>
#include <asm/mmu.h>
#include <asm/mmu_context.h>
#include <asm/tlbflush.h>
#include <asm/siginfo.h>
#include <asm/debug.h>

static inline bool notify_page_fault(struct pt_regs *regs)
{
        bool ret = false;

#ifdef CONFIG_KPROBES
        /* kprobe_running() needs smp_processor_id() */
        if (!user_mode(regs)) {
                preempt_disable();
                if (kprobe_running() && kprobe_fault_handler(regs, 11))
                        ret = true;
                preempt_enable();
        }
#endif /* CONFIG_KPROBES */

        if (unlikely(debugger_fault_handler(regs)))
                ret = true;

        return ret;
}

/*
 * Check whether the instruction at regs->nip is a store using
 * an update addressing form which will update r1.
 */
static bool store_updates_sp(struct pt_regs *regs)
{
        unsigned int inst;

        if (get_user(inst, (unsigned int __user *)regs->nip))
                return false;
        /* check for 1 in the rA field */
        if (((inst >> 16) & 0x1f) != 1)
                return false;
        /* check major opcode */
        switch (inst >> 26) {
        case 37:        /* stwu */
        case 39:        /* stbu */
        case 45:        /* sthu */
        case 53:        /* stfsu */
        case 55:        /* stfdu */
                return true;
        case 62:        /* std or stdu */
                return (inst & 3) == 1;
        case 31:
                /* check minor opcode */
                switch ((inst >> 1) & 0x3ff) {
                case 181:       /* stdux */
                case 183:       /* stwux */
                case 247:       /* stbux */
                case 439:       /* sthux */
                case 695:       /* stfsux */
                case 759:       /* stfdux */
                        return true;
                }
        }
        return false;
}
/*
 * do_page_fault error handling helpers
 */

static int
__bad_area_nosemaphore(struct pt_regs *regs, unsigned long address, int si_code)
{
        /*
         * If we are in kernel mode, bail out with a SEGV, this will
         * be caught by the assembly which will restore the non-volatile
         * registers before calling bad_page_fault()
         */
        if (!user_mode(regs))
                return SIGSEGV;

        _exception(SIGSEGV, regs, si_code, address);

        return 0;
}

static noinline int bad_area_nosemaphore(struct pt_regs *regs, unsigned long address)
{
        return __bad_area_nosemaphore(regs, address, SEGV_MAPERR);
}

static int __bad_area(struct pt_regs *regs, unsigned long address, int si_code)
{
        struct mm_struct *mm = current->mm;

        /*
         * 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);

        return __bad_area_nosemaphore(regs, address, si_code);
}

static noinline int bad_area(struct pt_regs *regs, unsigned long address)
{
        return __bad_area(regs, address, SEGV_MAPERR);
}

static noinline int bad_access(struct pt_regs *regs, unsigned long address)
{
        return __bad_area(regs, address, SEGV_ACCERR);
}

static int do_sigbus(struct pt_regs *regs, unsigned long address,
                     unsigned int fault)
{
        siginfo_t info;
        unsigned int lsb = 0;

        if (!user_mode(regs))
                return SIGBUS;

        current->thread.trap_nr = BUS_ADRERR;
        info.si_signo = SIGBUS;
        info.si_errno = 0;
        info.si_code = BUS_ADRERR;
        info.si_addr = (void __user *)address;
#ifdef CONFIG_MEMORY_FAILURE
        if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
                pr_err("MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
                        current->comm, current->pid, address);
                info.si_code = BUS_MCEERR_AR;
        }

        if (fault & VM_FAULT_HWPOISON_LARGE)
                lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
        if (fault & VM_FAULT_HWPOISON)
                lsb = PAGE_SHIFT;
#endif
        info.si_addr_lsb = lsb;
        force_sig_info(SIGBUS, &info, current);
        return 0;
}

static int mm_fault_error(struct pt_regs *regs, unsigned long addr, int fault)
{
        /*
         * Kernel page fault interrupted by SIGKILL. We have no reason to
         * continue processing.
         */
        if (fatal_signal_pending(current) && !user_mode(regs))
                return SIGKILL;

        /* Out of memory */
        if (fault & VM_FAULT_OOM) {
                /*
                 * We ran out of memory, or some other thing happened to us that
                 * made us unable to handle the page fault gracefully.
                 */
                if (!user_mode(regs))
                        return SIGSEGV;
                pagefault_out_of_memory();
        } else {
                if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|
                             VM_FAULT_HWPOISON_LARGE))
                        return do_sigbus(regs, addr, fault);
                else if (fault & VM_FAULT_SIGSEGV)
                        return bad_area_nosemaphore(regs, addr);
                else
                        BUG();
        }
        return 0;
}

/* Is this a bad kernel fault ? */
static bool bad_kernel_fault(bool is_exec, unsigned long error_code,
                             unsigned long address)
{
        if (is_exec && (error_code & (DSISR_NOEXEC_OR_G | DSISR_KEYFAULT))) {
                printk_ratelimited(KERN_CRIT "kernel tried to execute"
                                   " exec-protected page (%lx) -"
                                   "exploit attempt? (uid: %d)\n",
                                   address, from_kuid(&init_user_ns,
                                                      current_uid()));
        }
        return is_exec || (address >= TASK_SIZE);
}

static bool bad_stack_expansion(struct pt_regs *regs, unsigned long address,
                                struct vm_area_struct *vma,
                                bool store_update_sp)
{
        /*
         * N.B. The POWER/Open ABI allows programs to access up to
         * 288 bytes below the stack pointer.
         * The kernel signal delivery code writes up to about 1.5kB
         * below the stack pointer (r1) before decrementing it.
         * The exec code can write slightly over 640kB to the stack
         * before setting the user r1.  Thus we allow the stack to
         * expand to 1MB without further checks.
         */
        if (address + 0x100000 < vma->vm_end) {
                /* get user regs even if this fault is in kernel mode */
                struct pt_regs *uregs = current->thread.regs;
                if (uregs == NULL)
                        return true;

                /*
                 * A user-mode access to an address a long way below
                 * the stack pointer is only valid if the instruction
                 * is one which would update the stack pointer to the
                 * address accessed if the instruction completed,
                 * i.e. either stwu rs,n(r1) or stwux rs,r1,rb
                 * (or the byte, halfword, float or double forms).
                 *
                 * If we don't check this then any write to the area
                 * between the last mapped region and the stack will
                 * expand the stack rather than segfaulting.
                 */
                if (address + 2048 < uregs->gpr[1] && !store_update_sp)
                        return true;
        }
        return false;
}

static bool access_error(bool is_write, bool is_exec,
                         struct vm_area_struct *vma)
{
        /*
         * Allow execution from readable areas if the MMU does not
         * provide separate controls over reading and executing.
         *
         * Note: That code used to not be enabled for 4xx/BookE.
         * It is now as I/D cache coherency for these is done at
         * set_pte_at() time and I see no reason why the test
         * below wouldn't be valid on those processors. This -may-
         * break programs compiled with a really old ABI though.
         */
        if (is_exec) {
                return !(vma->vm_flags & VM_EXEC) &&
                        (cpu_has_feature(CPU_FTR_NOEXECUTE) ||
                         !(vma->vm_flags & (VM_READ | VM_WRITE)));
        }

        if (is_write) {
                if (unlikely(!(vma->vm_flags & VM_WRITE)))
                        return true;
                return false;
        }

        if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))))
                return true;

        return false;
}

#ifdef CONFIG_PPC_SMLPAR
static inline void cmo_account_page_fault(void)
{
        if (firmware_has_feature(FW_FEATURE_CMO)) {
                u32 page_ins;

                preempt_disable();
                page_ins = be32_to_cpu(get_lppaca()->page_ins);
                page_ins += 1 << PAGE_FACTOR;
                get_lppaca()->page_ins = cpu_to_be32(page_ins);
                preempt_enable();
        }
}
#else
static inline void cmo_account_page_fault(void) { }
#endif /* CONFIG_PPC_SMLPAR */

#ifdef CONFIG_PPC_STD_MMU
static void sanity_check_fault(bool is_write, unsigned long error_code)
{
        /*
         * For hash translation mode, we should never get a
         * PROTFAULT. Any update to pte to reduce access will result in us
         * removing the hash page table entry, thus resulting in a DSISR_NOHPTE
         * fault instead of DSISR_PROTFAULT.
         *
         * A pte update to relax the access will not result in a hash page table
         * entry invalidate and hence can result in DSISR_PROTFAULT.
         * ptep_set_access_flags() doesn't do a hpte flush. This is why we have
         * the special !is_write in the below conditional.
         *
         * For platforms that doesn't supports coherent icache and do support
         * per page noexec bit, we do setup things such that we do the
         * sync between D/I cache via fault. But that is handled via low level
         * hash fault code (hash_page_do_lazy_icache()) and we should not reach
         * here in such case.
         *
         * For wrong access that can result in PROTFAULT, the above vma->vm_flags
         * check should handle those and hence we should fall to the bad_area
         * handling correctly.
         *
         * For embedded with per page exec support that doesn't support coherent
         * icache we do get PROTFAULT and we handle that D/I cache sync in
         * set_pte_at while taking the noexec/prot fault. Hence this is WARN_ON
         * is conditional for server MMU.
         *
         * For radix, we can get prot fault for autonuma case, because radix
         * page table will have them marked noaccess for user.
         */
        if (!radix_enabled() && !is_write)
                WARN_ON_ONCE(error_code & DSISR_PROTFAULT);
}
#else
static void sanity_check_fault(bool is_write, unsigned long error_code) { }
#endif /* CONFIG_PPC_STD_MMU */

/*
 * Define the correct "is_write" bit in error_code based
 * on the processor family
 */
#if (defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
#define page_fault_is_write(__err)      ((__err) & ESR_DST)
#define page_fault_is_bad(__err)        (0)
#else
#define page_fault_is_write(__err)      ((__err) & DSISR_ISSTORE)
#if defined(CONFIG_PPC_8xx)
#define page_fault_is_bad(__err)        ((__err) & DSISR_NOEXEC_OR_G)
#elif defined(CONFIG_PPC64)
#define page_fault_is_bad(__err)        ((__err) & DSISR_BAD_FAULT_64S)
#else
#define page_fault_is_bad(__err)        ((__err) & DSISR_BAD_FAULT_32S)
#endif
#endif

/*
 * For 600- and 800-family processors, the error_code parameter is DSISR
 * for a data fault, SRR1 for an instruction fault. For 400-family processors
 * the error_code parameter is ESR for a data fault, 0 for an instruction
 * fault.
 * For 64-bit processors, the error_code parameter is
 *  - DSISR for a non-SLB data access fault,
 *  - SRR1 & 0x08000000 for a non-SLB instruction access fault
 *  - 0 any SLB fault.
 *
 * The return value is 0 if the fault was handled, or the signal
 * number if this is a kernel fault that can't be handled here.
 */
static int __do_page_fault(struct pt_regs *regs, unsigned long address,
                           unsigned long error_code)
{
        struct vm_area_struct * vma;
        struct mm_struct *mm = current->mm;
        unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
        int is_exec = TRAP(regs) == 0x400;
        int is_user = user_mode(regs);
        int is_write = page_fault_is_write(error_code);
        int fault, major = 0;
        bool store_update_sp = false;

        if (notify_page_fault(regs))
                return 0;

        if (unlikely(page_fault_is_bad(error_code))) {
                if (is_user) {
                        _exception(SIGBUS, regs, BUS_OBJERR, address);
                        return 0;
                }
                return SIGBUS;
        }

        /* Additional sanity check(s) */
        sanity_check_fault(is_write, error_code);

        /*
         * The kernel should never take an execute fault nor should it
         * take a page fault to a kernel address.
         */
        if (unlikely(!is_user && bad_kernel_fault(is_exec, error_code, address)))
                return SIGSEGV;

        /*
         * 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)) {
                if (is_user)
                        printk_ratelimited(KERN_ERR "Page fault in user mode"
                                           " with faulthandler_disabled()=%d"
                                           " mm=%p\n",
                                           faulthandler_disabled(), mm);
                return bad_area_nosemaphore(regs, address);
        }

        /* We restore the interrupt state now */
        if (!arch_irq_disabled_regs(regs))
                local_irq_enable();

        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);

        /*
         * We want to do this outside mmap_sem, because reading code around nip
         * can result in fault, which will cause a deadlock when called with
         * mmap_sem held
         */
        if (is_write && is_user)
                store_update_sp = store_updates_sp(regs);

        if (is_user)
                flags |= FAULT_FLAG_USER;
        if (is_write)
                flags |= FAULT_FLAG_WRITE;
        if (is_exec)
                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 (!is_user && !search_exception_tables(regs->nip))
                        return bad_area_nosemaphore(regs, address);

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))
                return bad_area(regs, address);
        if (likely(vma->vm_start <= address))
                goto good_area;
        if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
                return bad_area(regs, address);

        /* The stack is being expanded, check if it's valid */
        if (unlikely(bad_stack_expansion(regs, address, vma, store_update_sp)))
                return bad_area(regs, address);

        /* Try to expand it */
        if (unlikely(expand_stack(vma, address)))
                return bad_area(regs, address);

good_area:
        if (unlikely(access_error(is_write, is_exec, vma)))
                return bad_access(regs, address);

        /*
         * If for any reason at all we couldn't handle the fault,
         * make sure we exit gracefully rather than endlessly redo
         * the fault.
         */
        fault = handle_mm_fault(vma, address, flags);
        major |= fault & VM_FAULT_MAJOR;

        /*
         * Handle the retry right now, the mmap_sem has been released in that
         * case.
         */
        if (unlikely(fault & VM_FAULT_RETRY)) {
                /* We retry only once */
                if (flags & FAULT_FLAG_ALLOW_RETRY) {
                        /*
                         * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
                         * of starvation.
                         */
                        flags &= ~FAULT_FLAG_ALLOW_RETRY;
                        flags |= FAULT_FLAG_TRIED;
                        if (!fatal_signal_pending(current))
                                goto retry;
                }

                /*
                 * User mode? Just return to handle the fatal exception otherwise
                 * return to bad_page_fault
                 */
                return is_user ? 0 : SIGBUS;
        }

        up_read(&current->mm->mmap_sem);

        if (unlikely(fault & VM_FAULT_ERROR))
                return mm_fault_error(regs, address, fault);

        /*
         * Major/minor page fault accounting.
         */
        if (major) {
                current->maj_flt++;
                perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, regs, address);
                cmo_account_page_fault();
        } else {
                current->min_flt++;
                perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs, address);
        }
        return 0;
}
NOKPROBE_SYMBOL(__do_page_fault);

int do_page_fault(struct pt_regs *regs, unsigned long address,
                  unsigned long error_code)
{
        enum ctx_state prev_state = exception_enter();
        int rc = __do_page_fault(regs, address, error_code);
        exception_exit(prev_state);
        return rc;
}
NOKPROBE_SYMBOL(do_page_fault);

/*
 * bad_page_fault is called when we have a bad access from the kernel.
 * It is called from the DSI and ISI handlers in head.S and from some
 * of the procedures in traps.c.
 */
void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
{
        const struct exception_table_entry *entry;

        /* Are we prepared to handle this fault?  */
        if ((entry = search_exception_tables(regs->nip)) != NULL) {
                regs->nip = extable_fixup(entry);
                return;
        }

        /* kernel has accessed a bad area */

        switch (regs->trap) {
        case 0x300:
        case 0x380:
                printk(KERN_ALERT "Unable to handle kernel paging request for "
                        "data at address 0x%08lx\n", regs->dar);
                break;
        case 0x400:
        case 0x480:
                printk(KERN_ALERT "Unable to handle kernel paging request for "
                        "instruction fetch\n");
                break;
        case 0x600:
                printk(KERN_ALERT "Unable to handle kernel paging request for "
                        "unaligned access at address 0x%08lx\n", regs->dar);
                break;
        default:
                printk(KERN_ALERT "Unable to handle kernel paging request for "
                        "unknown fault\n");
                break;
        }
        printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
                regs->nip);

        if (task_stack_end_corrupted(current))
                printk(KERN_ALERT "Thread overran stack, or stack corrupted\n");

        die("Kernel access of bad area", regs, sig);
}