// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2020 ARM Ltd.
 */

#include <linux/bitops.h>
#include <linux/cpu.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/prctl.h>
#include <linux/sched.h>
#include <linux/sched/mm.h>
#include <linux/string.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/thread_info.h>
#include <linux/types.h>
#include <linux/uio.h>

#include <asm/barrier.h>
#include <asm/cpufeature.h>
#include <asm/mte.h>
#include <asm/ptrace.h>
#include <asm/sysreg.h>

static DEFINE_PER_CPU_READ_MOSTLY(u64, mte_tcf_preferred);

#ifdef CONFIG_KASAN_HW_TAGS
/* Whether the MTE asynchronous mode is enabled. */
DEFINE_STATIC_KEY_FALSE(mte_async_mode);
EXPORT_SYMBOL_GPL(mte_async_mode);
#endif

static void mte_sync_page_tags(struct page *page, pte_t old_pte,
                               bool check_swap, bool pte_is_tagged)
{
        if (check_swap && is_swap_pte(old_pte)) {
                swp_entry_t entry = pte_to_swp_entry(old_pte);

                if (!non_swap_entry(entry) && mte_restore_tags(entry, page))
                        return;
        }

        if (!pte_is_tagged)
                return;

        page_kasan_tag_reset(page);
        /*
         * We need smp_wmb() in between setting the flags and clearing the
         * tags because if another thread reads page->flags and builds a
         * tagged address out of it, there is an actual dependency to the
         * memory access, but on the current thread we do not guarantee that
         * the new page->flags are visible before the tags were updated.
         */
        smp_wmb();
        mte_clear_page_tags(page_address(page));
}

void mte_sync_tags(pte_t old_pte, pte_t pte)
{
        struct page *page = pte_page(pte);
        long i, nr_pages = compound_nr(page);
        bool check_swap = nr_pages == 1;
        bool pte_is_tagged = pte_tagged(pte);

        /* Early out if there's nothing to do */
        if (!check_swap && !pte_is_tagged)
                return;

        /* if PG_mte_tagged is set, tags have already been initialised */
        for (i = 0; i < nr_pages; i++, page++) {
                if (!test_and_set_bit(PG_mte_tagged, &page->flags))
                        mte_sync_page_tags(page, old_pte, check_swap,
                                           pte_is_tagged);
        }
}

int memcmp_pages(struct page *page1, struct page *page2)
{
        char *addr1, *addr2;
        int ret;

        addr1 = page_address(page1);
        addr2 = page_address(page2);
        ret = memcmp(addr1, addr2, PAGE_SIZE);

        if (!system_supports_mte() || ret)
                return ret;

        /*
         * If the page content is identical but at least one of the pages is
         * tagged, return non-zero to avoid KSM merging. If only one of the
         * pages is tagged, set_pte_at() may zero or change the tags of the
         * other page via mte_sync_tags().
         */
        if (test_bit(PG_mte_tagged, &page1->flags) ||
            test_bit(PG_mte_tagged, &page2->flags))
                return addr1 != addr2;

        return ret;
}

static inline void __mte_enable_kernel(const char *mode, unsigned long tcf)
{
        /* Enable MTE Sync Mode for EL1. */
        sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, tcf);
        isb();

        pr_info_once("MTE: enabled in %s mode at EL1\n", mode);
}

#ifdef CONFIG_KASAN_HW_TAGS
void mte_enable_kernel_sync(void)
{
        /*
         * Make sure we enter this function when no PE has set
         * async mode previously.
         */
        WARN_ONCE(system_uses_mte_async_mode(),
                        "MTE async mode enabled system wide!");

        __mte_enable_kernel("synchronous", SCTLR_ELx_TCF_SYNC);
}

void mte_enable_kernel_async(void)
{
        __mte_enable_kernel("asynchronous", SCTLR_ELx_TCF_ASYNC);

        /*
         * MTE async mode is set system wide by the first PE that
         * executes this function.
         *
         * Note: If in future KASAN acquires a runtime switching
         * mode in between sync and async, this strategy needs
         * to be reviewed.
         */
        if (!system_uses_mte_async_mode())
                static_branch_enable(&mte_async_mode);
}
#endif

#ifdef CONFIG_KASAN_HW_TAGS
void mte_check_tfsr_el1(void)
{
        u64 tfsr_el1 = read_sysreg_s(SYS_TFSR_EL1);

        if (unlikely(tfsr_el1 & SYS_TFSR_EL1_TF1)) {
                /*
                 * Note: isb() is not required after this direct write
                 * because there is no indirect read subsequent to it
                 * (per ARM DDI 0487F.c table D13-1).
                 */
                write_sysreg_s(0, SYS_TFSR_EL1);

                kasan_report_async();
        }
}
#endif

static void mte_update_sctlr_user(struct task_struct *task)
{
        /*
         * This must be called with preemption disabled and can only be called
         * on the current or next task since the CPU must match where the thread
         * is going to run. The caller is responsible for calling
         * update_sctlr_el1() later in the same preemption disabled block.
         */
        unsigned long sctlr = task->thread.sctlr_user;
        unsigned long mte_ctrl = task->thread.mte_ctrl;
        unsigned long pref, resolved_mte_tcf;

        pref = __this_cpu_read(mte_tcf_preferred);
        resolved_mte_tcf = (mte_ctrl & pref) ? pref : mte_ctrl;
        sctlr &= ~SCTLR_EL1_TCF0_MASK;
        if (resolved_mte_tcf & MTE_CTRL_TCF_ASYNC)
                sctlr |= SCTLR_EL1_TCF0_ASYNC;
        else if (resolved_mte_tcf & MTE_CTRL_TCF_SYNC)
                sctlr |= SCTLR_EL1_TCF0_SYNC;
        task->thread.sctlr_user = sctlr;
}

void mte_thread_init_user(void)
{
        if (!system_supports_mte())
                return;

        /* clear any pending asynchronous tag fault */
        dsb(ish);
        write_sysreg_s(0, SYS_TFSRE0_EL1);
        clear_thread_flag(TIF_MTE_ASYNC_FAULT);
        /* disable tag checking and reset tag generation mask */
        set_mte_ctrl(current, 0);
}

void mte_thread_switch(struct task_struct *next)
{
        if (!system_supports_mte())
                return;

        mte_update_sctlr_user(next);

        /*
         * Check if an async tag exception occurred at EL1.
         *
         * Note: On the context switch path we rely on the dsb() present
         * in __switch_to() to guarantee that the indirect writes to TFSR_EL1
         * are synchronized before this point.
         */
        isb();
        mte_check_tfsr_el1();
}

void mte_suspend_enter(void)
{
        if (!system_supports_mte())
                return;

        /*
         * The barriers are required to guarantee that the indirect writes
         * to TFSR_EL1 are synchronized before we report the state.
         */
        dsb(nsh);
        isb();

        /* Report SYS_TFSR_EL1 before suspend entry */
        mte_check_tfsr_el1();
}

long set_mte_ctrl(struct task_struct *task, unsigned long arg)
{
        u64 mte_ctrl = (~((arg & PR_MTE_TAG_MASK) >> PR_MTE_TAG_SHIFT) &
                        SYS_GCR_EL1_EXCL_MASK) << MTE_CTRL_GCR_USER_EXCL_SHIFT;

        if (!system_supports_mte())
                return 0;

        if (arg & PR_MTE_TCF_ASYNC)
                mte_ctrl |= MTE_CTRL_TCF_ASYNC;
        if (arg & PR_MTE_TCF_SYNC)
                mte_ctrl |= MTE_CTRL_TCF_SYNC;

        task->thread.mte_ctrl = mte_ctrl;
        if (task == current) {
                preempt_disable();
                mte_update_sctlr_user(task);
                update_sctlr_el1(task->thread.sctlr_user);
                preempt_enable();
        }

        return 0;
}

long get_mte_ctrl(struct task_struct *task)
{
        unsigned long ret;
        u64 mte_ctrl = task->thread.mte_ctrl;
        u64 incl = (~mte_ctrl >> MTE_CTRL_GCR_USER_EXCL_SHIFT) &
                   SYS_GCR_EL1_EXCL_MASK;

        if (!system_supports_mte())
                return 0;

        ret = incl << PR_MTE_TAG_SHIFT;
        if (mte_ctrl & MTE_CTRL_TCF_ASYNC)
                ret |= PR_MTE_TCF_ASYNC;
        if (mte_ctrl & MTE_CTRL_TCF_SYNC)
                ret |= PR_MTE_TCF_SYNC;

        return ret;
}

/*
 * Access MTE tags in another process' address space as given in mm. Update
 * the number of tags copied. Return 0 if any tags copied, error otherwise.
 * Inspired by __access_remote_vm().
 */
static int __access_remote_tags(struct mm_struct *mm, unsigned long addr,
                                struct iovec *kiov, unsigned int gup_flags)
{
        struct vm_area_struct *vma;
        void __user *buf = kiov->iov_base;
        size_t len = kiov->iov_len;
        int ret;
        int write = gup_flags & FOLL_WRITE;

        if (!access_ok(buf, len))
                return -EFAULT;

        if (mmap_read_lock_killable(mm))
                return -EIO;

        while (len) {
                unsigned long tags, offset;
                void *maddr;
                struct page *page = NULL;

                ret = get_user_pages_remote(mm, addr, 1, gup_flags, &page,
                                            &vma, NULL);
                if (ret <= 0)
                        break;

                /*
                 * Only copy tags if the page has been mapped as PROT_MTE
                 * (PG_mte_tagged set). Otherwise the tags are not valid and
                 * not accessible to user. Moreover, an mprotect(PROT_MTE)
                 * would cause the existing tags to be cleared if the page
                 * was never mapped with PROT_MTE.
                 */
                if (!(vma->vm_flags & VM_MTE)) {
                        ret = -EOPNOTSUPP;
                        put_page(page);
                        break;
                }
                WARN_ON_ONCE(!test_bit(PG_mte_tagged, &page->flags));

                /* limit access to the end of the page */
                offset = offset_in_page(addr);
                tags = min(len, (PAGE_SIZE - offset) / MTE_GRANULE_SIZE);

                maddr = page_address(page);
                if (write) {
                        tags = mte_copy_tags_from_user(maddr + offset, buf, tags);
                        set_page_dirty_lock(page);
                } else {
                        tags = mte_copy_tags_to_user(buf, maddr + offset, tags);
                }
                put_page(page);

                /* error accessing the tracer's buffer */
                if (!tags)
                        break;

                len -= tags;
                buf += tags;
                addr += tags * MTE_GRANULE_SIZE;
        }
        mmap_read_unlock(mm);

        /* return an error if no tags copied */
        kiov->iov_len = buf - kiov->iov_base;
        if (!kiov->iov_len) {
                /* check for error accessing the tracee's address space */
                if (ret <= 0)
                        return -EIO;
                else
                        return -EFAULT;
        }

        return 0;
}

/*
 * Copy MTE tags in another process' address space at 'addr' to/from tracer's
 * iovec buffer. Return 0 on success. Inspired by ptrace_access_vm().
 */
static int access_remote_tags(struct task_struct *tsk, unsigned long addr,
                              struct iovec *kiov, unsigned int gup_flags)
{
        struct mm_struct *mm;
        int ret;

        mm = get_task_mm(tsk);
        if (!mm)
                return -EPERM;

        if (!tsk->ptrace || (current != tsk->parent) ||
            ((get_dumpable(mm) != SUID_DUMP_USER) &&
             !ptracer_capable(tsk, mm->user_ns))) {
                mmput(mm);
                return -EPERM;
        }

        ret = __access_remote_tags(mm, addr, kiov, gup_flags);
        mmput(mm);

        return ret;
}

int mte_ptrace_copy_tags(struct task_struct *child, long request,
                         unsigned long addr, unsigned long data)
{
        int ret;
        struct iovec kiov;
        struct iovec __user *uiov = (void __user *)data;
        unsigned int gup_flags = FOLL_FORCE;

        if (!system_supports_mte())
                return -EIO;

        if (get_user(kiov.iov_base, &uiov->iov_base) ||
            get_user(kiov.iov_len, &uiov->iov_len))
                return -EFAULT;

        if (request == PTRACE_POKEMTETAGS)
                gup_flags |= FOLL_WRITE;

        /* align addr to the MTE tag granule */
        addr &= MTE_GRANULE_MASK;

        ret = access_remote_tags(child, addr, &kiov, gup_flags);
        if (!ret)
                ret = put_user(kiov.iov_len, &uiov->iov_len);

        return ret;
}

static ssize_t mte_tcf_preferred_show(struct device *dev,
                                      struct device_attribute *attr, char *buf)
{
        switch (per_cpu(mte_tcf_preferred, dev->id)) {
        case MTE_CTRL_TCF_ASYNC:
                return sysfs_emit(buf, "async\n");
        case MTE_CTRL_TCF_SYNC:
                return sysfs_emit(buf, "sync\n");
        default:
                return sysfs_emit(buf, "???\n");
        }
}

static ssize_t mte_tcf_preferred_store(struct device *dev,
                                       struct device_attribute *attr,
                                       const char *buf, size_t count)
{
        u64 tcf;

        if (sysfs_streq(buf, "async"))
                tcf = MTE_CTRL_TCF_ASYNC;
        else if (sysfs_streq(buf, "sync"))
                tcf = MTE_CTRL_TCF_SYNC;
        else
                return -EINVAL;

        device_lock(dev);
        per_cpu(mte_tcf_preferred, dev->id) = tcf;
        device_unlock(dev);

        return count;
}
static DEVICE_ATTR_RW(mte_tcf_preferred);

static int register_mte_tcf_preferred_sysctl(void)
{
        unsigned int cpu;

        if (!system_supports_mte())
                return 0;

        for_each_possible_cpu(cpu) {
                per_cpu(mte_tcf_preferred, cpu) = MTE_CTRL_TCF_ASYNC;
                device_create_file(get_cpu_device(cpu),
                                   &dev_attr_mte_tcf_preferred);
        }

        return 0;
}
subsys_initcall(register_mte_tcf_preferred_sysctl);