// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *  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)
 */

#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/string_choices.h>
#include <linux/types.h>
#include <linux/pagemap.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 <linux/kfence.h>
#include <linux/pkeys.h>

#include <asm/firmware.h>
#include <asm/interrupt.h>
#include <asm/page.h>
#include <asm/mmu.h>
#include <asm/mmu_context.h>
#include <asm/siginfo.h>
#include <asm/debug.h>
#include <asm/kup.h>
#include <asm/inst.h>


/*
 * 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, struct vm_area_struct *vma)
{

        /*
         * Something tried to access memory that isn't in our memory map..
         * Fix it, but check if it's kernel or user first..
         */
        if (mm)
                mmap_read_unlock(mm);
        else
                vma_end_read(vma);

        return __bad_area_nosemaphore(regs, address, si_code);
}

static noinline int bad_access_pkey(struct pt_regs *regs, unsigned long address,
                                    struct mm_struct *mm,
                                    struct vm_area_struct *vma)
{
        int pkey;

        /*
         * We don't try to fetch the pkey from page table because reading
         * page table without locking doesn't guarantee stable pte value.
         * Hence the pkey value that we return to userspace can be different
         * from the pkey that actually caused access error.
         *
         * 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 AMR 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_lock, etc...
         * 6. T1   : reaches here, sees vma_pkey(vma)=5, when we really
         *           faulted on a pte with its pkey=4.
         */
        pkey = vma_pkey(vma);

        if (mm)
                mmap_read_unlock(mm);
        else
                vma_end_read(vma);

        /*
         * 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_pkey(regs, address, pkey);

        return 0;
}

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

static int do_sigbus(struct pt_regs *regs, unsigned long address,
                     vm_fault_t fault)
{
        if (!user_mode(regs))
                return SIGBUS;

        current->thread.trap_nr = BUS_ADRERR;
#ifdef CONFIG_MEMORY_FAILURE
        if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
                unsigned int lsb = 0; /* shutup gcc */

                pr_err("MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
                        current->comm, current->pid, 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;

                force_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb);
                return 0;
        }

#endif
        force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
        return 0;
}

static int mm_fault_error(struct pt_regs *regs, unsigned long addr,
                                vm_fault_t 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(struct pt_regs *regs, unsigned long error_code,
                             unsigned long address, bool is_write)
{
        int is_exec = TRAP(regs) == INTERRUPT_INST_STORAGE;

        if (is_exec) {
                pr_crit_ratelimited("kernel tried to execute %s page (%lx) - exploit attempt? (uid: %d)\n",
                                    address >= TASK_SIZE ? "exec-protected" : "user",
                                    address,
                                    from_kuid(&init_user_ns, current_uid()));

                // Kernel exec fault is always bad
                return true;
        }

        // Kernel fault on kernel address is bad
        if (address >= TASK_SIZE)
                return true;

        // Read/write fault blocked by KUAP is bad, it can never succeed.
        if (bad_kuap_fault(regs, address, is_write)) {
                pr_crit_ratelimited("Kernel attempted to %s user page (%lx) - exploit attempt? (uid: %d)\n",
                                    str_write_read(is_write), address,
                                    from_kuid(&init_user_ns, current_uid()));

                // Fault on user outside of certain regions (eg. copy_tofrom_user()) is bad
                if (!search_exception_tables(regs->nip))
                        return true;

                // Read/write fault in a valid region (the exception table search passed
                // above), but blocked by KUAP is bad, it can never succeed.
                return WARN(true, "Bug: %s fault blocked by KUAP!", is_write ? "Write" : "Read");
        }

        // What's left? Kernel fault on user and allowed by KUAP in the faulting context.
        return false;
}

static bool access_pkey_error(bool is_write, bool is_exec, bool is_pkey,
                              struct vm_area_struct *vma)
{
        /*
         * Make sure to check the VMA so that we do not perform
         * faults just to hit a pkey fault as soon as we fill in a
         * page. Only called for current mm, hence foreign == 0
         */
        if (!arch_vma_access_permitted(vma, is_write, is_exec, 0))
                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;
        }

        /*
         * VM_READ, VM_WRITE and VM_EXEC may imply read permissions, as
         * defined in protection_map[].  In that case Read faults can only be
         * caused by a PROT_NONE mapping. However a non exec access on a
         * VM_EXEC only mapping is invalid anyway, so report it as such.
         */
        if (unlikely(!vma_is_accessible(vma)))
                return true;

        if ((vma->vm_flags & VM_ACCESS_FLAGS) == VM_EXEC)
                return true;

        /*
         * We should ideally do the vma pkey access check here. But in the
         * fault path, handle_mm_fault() also does the same check. To avoid
         * these multiple checks, we skip it here and handle access error due
         * to pkeys later.
         */
        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 */

static void sanity_check_fault(bool is_write, bool is_user,
                               unsigned long error_code, unsigned long address)
{
        /*
         * Userspace trying to access kernel address, we get PROTFAULT for that.
         */
        if (is_user && address >= TASK_SIZE) {
                if ((long)address == -1)
                        return;

                pr_crit_ratelimited("%s[%d]: User access of kernel address (%lx) - exploit attempt? (uid: %d)\n",
                                   current->comm, current->pid, address,
                                   from_kuid(&init_user_ns, current_uid()));
                return;
        }

        if (!IS_ENABLED(CONFIG_PPC_BOOK3S))
                return;

        /*
         * 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)
                return;

        WARN_ON_ONCE(error_code & DSISR_PROTFAULT);
}

/*
 * Define the correct "is_write" bit in error_code based
 * on the processor family
 */
#ifdef CONFIG_BOOKE
#define page_fault_is_write(__err)      ((__err) & ESR_DST)
#else
#define page_fault_is_write(__err)      ((__err) & DSISR_ISSTORE)
#endif

#ifdef CONFIG_BOOKE
#define page_fault_is_bad(__err)        (0)
#elif defined(CONFIG_PPC_8xx)
#define page_fault_is_bad(__err)        ((__err) & DSISR_NOEXEC_OR_G)
#elif defined(CONFIG_PPC64)
static int page_fault_is_bad(unsigned long err)
{
        unsigned long flag = DSISR_BAD_FAULT_64S;

        /*
         * PAPR+ v2.11 § 14.15.3.4.1 (unreleased)
         * If byte 0, bit 3 of pi-attribute-specifier-type in
         * ibm,pi-features property is defined, ignore the DSI error
         * which is caused by the paste instruction on the
         * suspended NX window.
         */
        if (mmu_has_feature(MMU_FTR_NX_DSI))
                flag &= ~DSISR_BAD_COPYPASTE;

        return err & flag;
}
#else
#define page_fault_is_bad(__err)        ((__err) & DSISR_BAD_FAULT_32S)
#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 data access
 * fault, SRR1 & 0x08000000 for an instruction access 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_DEFAULT;
        int is_exec = TRAP(regs) == INTERRUPT_INST_STORAGE;
        int is_user = user_mode(regs);
        int is_write = page_fault_is_write(error_code);
        vm_fault_t fault, major = 0;
        bool kprobe_fault = kprobe_page_fault(regs, 11);

        if (unlikely(debugger_fault_handler(regs) || kprobe_fault))
                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, is_user, error_code, address);

        /*
         * The kernel should never take an execute fault nor should it
         * take a page fault to a kernel address or a page fault to a user
         * address outside of dedicated places.
         *
         * Rather than kfence directly reporting false negatives, search whether
         * the NIP belongs to the fixup table for cases where fault could come
         * from functions like copy_from_kernel_nofault().
         */
        if (unlikely(!is_user && bad_kernel_fault(regs, error_code, address, is_write))) {
                if (is_kfence_address((void *)address) &&
                    !search_exception_tables(instruction_pointer(regs)) &&
                    kfence_handle_page_fault(address, is_write, regs))
                        return 0;

                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);
        }

        interrupt_cond_local_irq_enable(regs);

        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);

        /*
         * We want to do this outside mmap_lock, because reading code around nip
         * can result in fault, which will cause a deadlock when called with
         * mmap_lock held
         */
        if (is_user)
                flags |= FAULT_FLAG_USER;
        if (is_write)
                flags |= FAULT_FLAG_WRITE;
        if (is_exec)
                flags |= FAULT_FLAG_INSTRUCTION;

        if (!(flags & FAULT_FLAG_USER))
                goto lock_mmap;

        vma = lock_vma_under_rcu(mm, address);
        if (!vma)
                goto lock_mmap;

        if (unlikely(access_pkey_error(is_write, is_exec,
                                       (error_code & DSISR_KEYFAULT), vma))) {
                count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
                return bad_access_pkey(regs, address, NULL, vma);
        }

        if (unlikely(access_error(is_write, is_exec, vma))) {
                count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
                return bad_access(regs, address, NULL, vma);
        }

        fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, regs);
        if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
                vma_end_read(vma);

        if (!(fault & VM_FAULT_RETRY)) {
                count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
                goto done;
        }
        count_vm_vma_lock_event(VMA_LOCK_RETRY);
        if (fault & VM_FAULT_MAJOR)
                flags |= FAULT_FLAG_TRIED;

        if (fault_signal_pending(fault, regs))
                return user_mode(regs) ? 0 : SIGBUS;

lock_mmap:

        /* 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_lock
         * 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. lock_mm_and_find_vma() handles that logic.
         */
retry:
        vma = lock_mm_and_find_vma(mm, address, regs);
        if (unlikely(!vma))
                return bad_area_nosemaphore(regs, address);

        if (unlikely(access_pkey_error(is_write, is_exec,
                                       (error_code & DSISR_KEYFAULT), vma)))
                return bad_access_pkey(regs, address, mm, vma);

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

        /*
         * 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, regs);

        major |= fault & VM_FAULT_MAJOR;

        if (fault_signal_pending(fault, regs))
                return user_mode(regs) ? 0 : SIGBUS;

        /* The fault is fully completed (including releasing mmap lock) */
        if (fault & VM_FAULT_COMPLETED)
                goto out;

        /*
         * Handle the retry right now, the mmap_lock has been released in that
         * case.
         */
        if (unlikely(fault & VM_FAULT_RETRY)) {
                flags |= FAULT_FLAG_TRIED;
                goto retry;
        }

        mmap_read_unlock(current->mm);

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

out:
        /*
         * Major/minor page fault accounting.
         */
        if (major)
                cmo_account_page_fault();

        return 0;
}
NOKPROBE_SYMBOL(___do_page_fault);

static __always_inline void __do_page_fault(struct pt_regs *regs)
{
        long err;

        err = ___do_page_fault(regs, regs->dar, regs->dsisr);
        if (unlikely(err))
                bad_page_fault(regs, err);
}

DEFINE_INTERRUPT_HANDLER(do_page_fault)
{
        __do_page_fault(regs);
}

#ifdef CONFIG_PPC_BOOK3S_64
/* Same as do_page_fault but interrupt entry has already run in do_hash_fault */
void hash__do_page_fault(struct pt_regs *regs)
{
        __do_page_fault(regs);
}
NOKPROBE_SYMBOL(hash__do_page_fault);
#endif

/*
 * 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.
 */
static void __bad_page_fault(struct pt_regs *regs, int sig)
{
        int is_write = page_fault_is_write(regs->dsisr);
        const char *msg;

        /* kernel has accessed a bad area */

        if (regs->dar < PAGE_SIZE)
                msg = "Kernel NULL pointer dereference";
        else
                msg = "Unable to handle kernel data access";

        switch (TRAP(regs)) {
        case INTERRUPT_DATA_STORAGE:
        case INTERRUPT_H_DATA_STORAGE:
                pr_alert("BUG: %s on %s at 0x%08lx\n", msg,
                         str_write_read(is_write), regs->dar);
                break;
        case INTERRUPT_DATA_SEGMENT:
                pr_alert("BUG: %s at 0x%08lx\n", msg, regs->dar);
                break;
        case INTERRUPT_INST_STORAGE:
        case INTERRUPT_INST_SEGMENT:
                pr_alert("BUG: Unable to handle kernel instruction fetch%s",
                         regs->nip < PAGE_SIZE ? " (NULL pointer?)\n" : "\n");
                break;
        case INTERRUPT_ALIGNMENT:
                pr_alert("BUG: Unable to handle kernel unaligned access at 0x%08lx\n",
                         regs->dar);
                break;
        default:
                pr_alert("BUG: Unable to handle unknown paging fault at 0x%08lx\n",
                         regs->dar);
                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);
}

void bad_page_fault(struct pt_regs *regs, int sig)
{
        const struct exception_table_entry *entry;

        /* Are we prepared to handle this fault?  */
        entry = search_exception_tables(instruction_pointer(regs));
        if (entry)
                instruction_pointer_set(regs, extable_fixup(entry));
        else
                __bad_page_fault(regs, sig);
}

#ifdef CONFIG_PPC_BOOK3S_64
DEFINE_INTERRUPT_HANDLER(do_bad_page_fault_segv)
{
        bad_page_fault(regs, SIGSEGV);
}

/*
 * In radix, segment interrupts indicate the EA is not addressable by the
 * page table geometry, so they are always sent here.
 *
 * In hash, this is called if do_slb_fault returns error. Typically it is
 * because the EA was outside the region allowed by software.
 */
DEFINE_INTERRUPT_HANDLER(do_bad_segment_interrupt)
{
        int err = regs->result;

        if (err == -EFAULT) {
                if (user_mode(regs))
                        _exception(SIGSEGV, regs, SEGV_BNDERR, regs->dar);
                else
                        bad_page_fault(regs, SIGSEGV);
        } else if (err == -EINVAL) {
                unrecoverable_exception(regs);
        } else {
                BUG();
        }
}
#endif