/**
 * kmemcheck - a heavyweight memory checker for the linux kernel
 * Copyright (C) 2007, 2008  Vegard Nossum <vegardno@ifi.uio.no>
 * (With a lot of help from Ingo Molnar and Pekka Enberg.)
 *
 * 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.
 */

#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/kallsyms.h>
#include <linux/kernel.h>
#include <linux/kmemcheck.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/page-flags.h>
#include <linux/percpu.h>
#include <linux/ptrace.h>
#include <linux/string.h>
#include <linux/types.h>

#include <asm/cacheflush.h>
#include <asm/kmemcheck.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>

#include "error.h"
#include "opcode.h"
#include "pte.h"
#include "selftest.h"
#include "shadow.h"


#ifdef CONFIG_KMEMCHECK_DISABLED_BY_DEFAULT
#  define KMEMCHECK_ENABLED 0
#endif

#ifdef CONFIG_KMEMCHECK_ENABLED_BY_DEFAULT
#  define KMEMCHECK_ENABLED 1
#endif

#ifdef CONFIG_KMEMCHECK_ONESHOT_BY_DEFAULT
#  define KMEMCHECK_ENABLED 2
#endif

int kmemcheck_enabled = KMEMCHECK_ENABLED;

int __init kmemcheck_init(void)
{
#ifdef CONFIG_SMP
        /*
         * Limit SMP to use a single CPU. We rely on the fact that this code
         * runs before SMP is set up.
         */
        if (setup_max_cpus > 1) {
                printk(KERN_INFO
                        "kmemcheck: Limiting number of CPUs to 1.\n");
                setup_max_cpus = 1;
        }
#endif

        if (!kmemcheck_selftest()) {
                printk(KERN_INFO "kmemcheck: self-tests failed; disabling\n");
                kmemcheck_enabled = 0;
                return -EINVAL;
        }

        printk(KERN_INFO "kmemcheck: Initialized\n");
        return 0;
}

early_initcall(kmemcheck_init);

/*
 * We need to parse the kmemcheck= option before any memory is allocated.
 */
static int __init param_kmemcheck(char *str)
{
        if (!str)
                return -EINVAL;

        sscanf(str, "%d", &kmemcheck_enabled);
        return 0;
}

early_param("kmemcheck", param_kmemcheck);

int kmemcheck_show_addr(unsigned long address)
{
        pte_t *pte;

        pte = kmemcheck_pte_lookup(address);
        if (!pte)
                return 0;

        set_pte(pte, __pte(pte_val(*pte) | _PAGE_PRESENT));
        __flush_tlb_one(address);
        return 1;
}

int kmemcheck_hide_addr(unsigned long address)
{
        pte_t *pte;

        pte = kmemcheck_pte_lookup(address);
        if (!pte)
                return 0;

        set_pte(pte, __pte(pte_val(*pte) & ~_PAGE_PRESENT));
        __flush_tlb_one(address);
        return 1;
}

struct kmemcheck_context {
        bool busy;
        int balance;

        /*
         * There can be at most two memory operands to an instruction, but
         * each address can cross a page boundary -- so we may need up to
         * four addresses that must be hidden/revealed for each fault.
         */
        unsigned long addr[4];
        unsigned long n_addrs;
        unsigned long flags;

        /* Data size of the instruction that caused a fault. */
        unsigned int size;
};

static DEFINE_PER_CPU(struct kmemcheck_context, kmemcheck_context);

bool kmemcheck_active(struct pt_regs *regs)
{
        struct kmemcheck_context *data = &__get_cpu_var(kmemcheck_context);

        return data->balance > 0;
}

/* Save an address that needs to be shown/hidden */
static void kmemcheck_save_addr(unsigned long addr)
{
        struct kmemcheck_context *data = &__get_cpu_var(kmemcheck_context);

        BUG_ON(data->n_addrs >= ARRAY_SIZE(data->addr));
        data->addr[data->n_addrs++] = addr;
}

static unsigned int kmemcheck_show_all(void)
{
        struct kmemcheck_context *data = &__get_cpu_var(kmemcheck_context);
        unsigned int i;
        unsigned int n;

        n = 0;
        for (i = 0; i < data->n_addrs; ++i)
                n += kmemcheck_show_addr(data->addr[i]);

        return n;
}

static unsigned int kmemcheck_hide_all(void)
{
        struct kmemcheck_context *data = &__get_cpu_var(kmemcheck_context);
        unsigned int i;
        unsigned int n;

        n = 0;
        for (i = 0; i < data->n_addrs; ++i)
                n += kmemcheck_hide_addr(data->addr[i]);

        return n;
}

/*
 * Called from the #PF handler.
 */
void kmemcheck_show(struct pt_regs *regs)
{
        struct kmemcheck_context *data = &__get_cpu_var(kmemcheck_context);

        BUG_ON(!irqs_disabled());

        if (unlikely(data->balance != 0)) {
                kmemcheck_show_all();
                kmemcheck_error_save_bug(regs);
                data->balance = 0;
                return;
        }

        /*
         * None of the addresses actually belonged to kmemcheck. Note that
         * this is not an error.
         */
        if (kmemcheck_show_all() == 0)
                return;

        ++data->balance;

        /*
         * The IF needs to be cleared as well, so that the faulting
         * instruction can run "uninterrupted". Otherwise, we might take
         * an interrupt and start executing that before we've had a chance
         * to hide the page again.
         *
         * NOTE: In the rare case of multiple faults, we must not override
         * the original flags:
         */
        if (!(regs->flags & X86_EFLAGS_TF))
                data->flags = regs->flags;

        regs->flags |= X86_EFLAGS_TF;
        regs->flags &= ~X86_EFLAGS_IF;
}

/*
 * Called from the #DB handler.
 */
void kmemcheck_hide(struct pt_regs *regs)
{
        struct kmemcheck_context *data = &__get_cpu_var(kmemcheck_context);
        int n;

        BUG_ON(!irqs_disabled());

        if (unlikely(data->balance != 1)) {
                kmemcheck_show_all();
                kmemcheck_error_save_bug(regs);
                data->n_addrs = 0;
                data->balance = 0;

                if (!(data->flags & X86_EFLAGS_TF))
                        regs->flags &= ~X86_EFLAGS_TF;
                if (data->flags & X86_EFLAGS_IF)
                        regs->flags |= X86_EFLAGS_IF;
                return;
        }

        if (kmemcheck_enabled)
                n = kmemcheck_hide_all();
        else
                n = kmemcheck_show_all();

        if (n == 0)
                return;

        --data->balance;

        data->n_addrs = 0;

        if (!(data->flags & X86_EFLAGS_TF))
                regs->flags &= ~X86_EFLAGS_TF;
        if (data->flags & X86_EFLAGS_IF)
                regs->flags |= X86_EFLAGS_IF;
}

void kmemcheck_show_pages(struct page *p, unsigned int n)
{
        unsigned int i;

        for (i = 0; i < n; ++i) {
                unsigned long address;
                pte_t *pte;
                unsigned int level;

                address = (unsigned long) page_address(&p[i]);
                pte = lookup_address(address, &level);
                BUG_ON(!pte);
                BUG_ON(level != PG_LEVEL_4K);

                set_pte(pte, __pte(pte_val(*pte) | _PAGE_PRESENT));
                set_pte(pte, __pte(pte_val(*pte) & ~_PAGE_HIDDEN));
                __flush_tlb_one(address);
        }
}

bool kmemcheck_page_is_tracked(struct page *p)
{
        /* This will also check the "hidden" flag of the PTE. */
        return kmemcheck_pte_lookup((unsigned long) page_address(p));
}

void kmemcheck_hide_pages(struct page *p, unsigned int n)
{
        unsigned int i;

        for (i = 0; i < n; ++i) {
                unsigned long address;
                pte_t *pte;
                unsigned int level;

                address = (unsigned long) page_address(&p[i]);
                pte = lookup_address(address, &level);
                BUG_ON(!pte);
                BUG_ON(level != PG_LEVEL_4K);

                set_pte(pte, __pte(pte_val(*pte) & ~_PAGE_PRESENT));
                set_pte(pte, __pte(pte_val(*pte) | _PAGE_HIDDEN));
                __flush_tlb_one(address);
        }
}

/* Access may NOT cross page boundary */
static void kmemcheck_read_strict(struct pt_regs *regs,
        unsigned long addr, unsigned int size)
{
        void *shadow;
        enum kmemcheck_shadow status;

        shadow = kmemcheck_shadow_lookup(addr);
        if (!shadow)
                return;

        kmemcheck_save_addr(addr);
        status = kmemcheck_shadow_test(shadow, size);
        if (status == KMEMCHECK_SHADOW_INITIALIZED)
                return;

        if (kmemcheck_enabled)
                kmemcheck_error_save(status, addr, size, regs);

        if (kmemcheck_enabled == 2)
                kmemcheck_enabled = 0;

        /* Don't warn about it again. */
        kmemcheck_shadow_set(shadow, size);
}

bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size)
{
        enum kmemcheck_shadow status;
        void *shadow;

        shadow = kmemcheck_shadow_lookup(addr);
        if (!shadow)
                return true;

        status = kmemcheck_shadow_test_all(shadow, size);

        return status == KMEMCHECK_SHADOW_INITIALIZED;
}

/* Access may cross page boundary */
static void kmemcheck_read(struct pt_regs *regs,
        unsigned long addr, unsigned int size)
{
        unsigned long page = addr & PAGE_MASK;
        unsigned long next_addr = addr + size - 1;
        unsigned long next_page = next_addr & PAGE_MASK;

        if (likely(page == next_page)) {
                kmemcheck_read_strict(regs, addr, size);
                return;
        }

        /*
         * What we do is basically to split the access across the
         * two pages and handle each part separately. Yes, this means
         * that we may now see reads that are 3 + 5 bytes, for
         * example (and if both are uninitialized, there will be two
         * reports), but it makes the code a lot simpler.
         */
        kmemcheck_read_strict(regs, addr, next_page - addr);
        kmemcheck_read_strict(regs, next_page, next_addr - next_page);
}

static void kmemcheck_write_strict(struct pt_regs *regs,
        unsigned long addr, unsigned int size)
{
        void *shadow;

        shadow = kmemcheck_shadow_lookup(addr);
        if (!shadow)
                return;

        kmemcheck_save_addr(addr);
        kmemcheck_shadow_set(shadow, size);
}

static void kmemcheck_write(struct pt_regs *regs,
        unsigned long addr, unsigned int size)
{
        unsigned long page = addr & PAGE_MASK;
        unsigned long next_addr = addr + size - 1;
        unsigned long next_page = next_addr & PAGE_MASK;

        if (likely(page == next_page)) {
                kmemcheck_write_strict(regs, addr, size);
                return;
        }

        /* See comment in kmemcheck_read(). */
        kmemcheck_write_strict(regs, addr, next_page - addr);
        kmemcheck_write_strict(regs, next_page, next_addr - next_page);
}

/*
 * Copying is hard. We have two addresses, each of which may be split across
 * a page (and each page will have different shadow addresses).
 */
static void kmemcheck_copy(struct pt_regs *regs,
        unsigned long src_addr, unsigned long dst_addr, unsigned int size)
{
        uint8_t shadow[8];
        enum kmemcheck_shadow status;

        unsigned long page;
        unsigned long next_addr;
        unsigned long next_page;

        uint8_t *x;
        unsigned int i;
        unsigned int n;

        BUG_ON(size > sizeof(shadow));

        page = src_addr & PAGE_MASK;
        next_addr = src_addr + size - 1;
        next_page = next_addr & PAGE_MASK;

        if (likely(page == next_page)) {
                /* Same page */
                x = kmemcheck_shadow_lookup(src_addr);
                if (x) {
                        kmemcheck_save_addr(src_addr);
                        for (i = 0; i < size; ++i)
                                shadow[i] = x[i];
                } else {
                        for (i = 0; i < size; ++i)
                                shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
                }
        } else {
                n = next_page - src_addr;
                BUG_ON(n > sizeof(shadow));

                /* First page */
                x = kmemcheck_shadow_lookup(src_addr);
                if (x) {
                        kmemcheck_save_addr(src_addr);
                        for (i = 0; i < n; ++i)
                                shadow[i] = x[i];
                } else {
                        /* Not tracked */
                        for (i = 0; i < n; ++i)
                                shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
                }

                /* Second page */
                x = kmemcheck_shadow_lookup(next_page);
                if (x) {
                        kmemcheck_save_addr(next_page);
                        for (i = n; i < size; ++i)
                                shadow[i] = x[i - n];
                } else {
                        /* Not tracked */
                        for (i = n; i < size; ++i)
                                shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
                }
        }

        page = dst_addr & PAGE_MASK;
        next_addr = dst_addr + size - 1;
        next_page = next_addr & PAGE_MASK;

        if (likely(page == next_page)) {
                /* Same page */
                x = kmemcheck_shadow_lookup(dst_addr);
                if (x) {
                        kmemcheck_save_addr(dst_addr);
                        for (i = 0; i < size; ++i) {
                                x[i] = shadow[i];
                                shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
                        }
                }
        } else {
                n = next_page - dst_addr;
                BUG_ON(n > sizeof(shadow));

                /* First page */
                x = kmemcheck_shadow_lookup(dst_addr);
                if (x) {
                        kmemcheck_save_addr(dst_addr);
                        for (i = 0; i < n; ++i) {
                                x[i] = shadow[i];
                                shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
                        }
                }

                /* Second page */
                x = kmemcheck_shadow_lookup(next_page);
                if (x) {
                        kmemcheck_save_addr(next_page);
                        for (i = n; i < size; ++i) {
                                x[i - n] = shadow[i];
                                shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
                        }
                }
        }

        status = kmemcheck_shadow_test(shadow, size);
        if (status == KMEMCHECK_SHADOW_INITIALIZED)
                return;

        if (kmemcheck_enabled)
                kmemcheck_error_save(status, src_addr, size, regs);

        if (kmemcheck_enabled == 2)
                kmemcheck_enabled = 0;
}

enum kmemcheck_method {
        KMEMCHECK_READ,
        KMEMCHECK_WRITE,
};

static void kmemcheck_access(struct pt_regs *regs,
        unsigned long fallback_address, enum kmemcheck_method fallback_method)
{
        const uint8_t *insn;
        const uint8_t *insn_primary;
        unsigned int size;

        struct kmemcheck_context *data = &__get_cpu_var(kmemcheck_context);

        /* Recursive fault -- ouch. */
        if (data->busy) {
                kmemcheck_show_addr(fallback_address);
                kmemcheck_error_save_bug(regs);
                return;
        }

        data->busy = true;

        insn = (const uint8_t *) regs->ip;
        insn_primary = kmemcheck_opcode_get_primary(insn);

        kmemcheck_opcode_decode(insn, &size);

        switch (insn_primary[0]) {
#ifdef CONFIG_KMEMCHECK_BITOPS_OK
                /* AND, OR, XOR */
                /*
                 * Unfortunately, these instructions have to be excluded from
                 * our regular checking since they access only some (and not
                 * all) bits. This clears out "bogus" bitfield-access warnings.
                 */
        case 0x80:
        case 0x81:
        case 0x82:
        case 0x83:
                switch ((insn_primary[1] >> 3) & 7) {
                        /* OR */
                case 1:
                        /* AND */
                case 4:
                        /* XOR */
                case 6:
                        kmemcheck_write(regs, fallback_address, size);
                        goto out;

                        /* ADD */
                case 0:
                        /* ADC */
                case 2:
                        /* SBB */
                case 3:
                        /* SUB */
                case 5:
                        /* CMP */
                case 7:
                        break;
                }
                break;
#endif

                /* MOVS, MOVSB, MOVSW, MOVSD */
        case 0xa4:
        case 0xa5:
                /*
                 * These instructions are special because they take two
                 * addresses, but we only get one page fault.
                 */
                kmemcheck_copy(regs, regs->si, regs->di, size);
                goto out;

                /* CMPS, CMPSB, CMPSW, CMPSD */
        case 0xa6:
        case 0xa7:
                kmemcheck_read(regs, regs->si, size);
                kmemcheck_read(regs, regs->di, size);
                goto out;
        }

        /*
         * If the opcode isn't special in any way, we use the data from the
         * page fault handler to determine the address and type of memory
         * access.
         */
        switch (fallback_method) {
        case KMEMCHECK_READ:
                kmemcheck_read(regs, fallback_address, size);
                goto out;
        case KMEMCHECK_WRITE:
                kmemcheck_write(regs, fallback_address, size);
                goto out;
        }

out:
        data->busy = false;
}

bool kmemcheck_fault(struct pt_regs *regs, unsigned long address,
        unsigned long error_code)
{
        pte_t *pte;

        /*
         * XXX: Is it safe to assume that memory accesses from virtual 86
         * mode or non-kernel code segments will _never_ access kernel
         * memory (e.g. tracked pages)? For now, we need this to avoid
         * invoking kmemcheck for PnP BIOS calls.
         */
        if (regs->flags & X86_VM_MASK)
                return false;
        if (regs->cs != __KERNEL_CS)
                return false;

        pte = kmemcheck_pte_lookup(address);
        if (!pte)
                return false;

        WARN_ON_ONCE(in_nmi());

        if (error_code & 2)
                kmemcheck_access(regs, address, KMEMCHECK_WRITE);
        else
                kmemcheck_access(regs, address, KMEMCHECK_READ);

        kmemcheck_show(regs);
        return true;
}

bool kmemcheck_trap(struct pt_regs *regs)
{
        if (!kmemcheck_active(regs))
                return false;

        /* We're done. */
        kmemcheck_hide(regs);
        return true;
}