// SPDX-License-Identifier: GPL-2.0

/*
 * Tests for mremap w/ MREMAP_DONTUNMAP.
 *
 * Copyright 2020, Brian Geffon <bgeffon@google.com>
 */
#define _GNU_SOURCE
#include <sys/mman.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "../kselftest.h"

#ifndef MREMAP_DONTUNMAP
#define MREMAP_DONTUNMAP 4
#endif

unsigned long page_size;
char *page_buffer;

static void dump_maps(void)
{
        char cmd[32];

        snprintf(cmd, sizeof(cmd), "cat /proc/%d/maps", getpid());
        system(cmd);
}

#define BUG_ON(condition, description)                                        \
        do {                                                                  \
                if (condition) {                                              \
                        fprintf(stderr, "[FAIL]\t%s():%d\t%s:%s\n", __func__, \
                                __LINE__, (description), strerror(errno));    \
                        dump_maps();                                      \
                        exit(1);                                              \
                }                                                             \
        } while (0)

// Try a simple operation for to "test" for kernel support this prevents
// reporting tests as failed when it's run on an older kernel.
static int kernel_support_for_mremap_dontunmap()
{
        int ret = 0;
        unsigned long num_pages = 1;
        void *source_mapping = mmap(NULL, num_pages * page_size, PROT_NONE,
                                    MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
        BUG_ON(source_mapping == MAP_FAILED, "mmap");

        // This simple remap should only fail if MREMAP_DONTUNMAP isn't
        // supported.
        void *dest_mapping =
            mremap(source_mapping, num_pages * page_size, num_pages * page_size,
                   MREMAP_DONTUNMAP | MREMAP_MAYMOVE, 0);
        if (dest_mapping == MAP_FAILED) {
                ret = errno;
        } else {
                BUG_ON(munmap(dest_mapping, num_pages * page_size) == -1,
                       "unable to unmap destination mapping");
        }

        BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
               "unable to unmap source mapping");
        return ret;
}

// This helper will just validate that an entire mapping contains the expected
// byte.
static int check_region_contains_byte(void *addr, unsigned long size, char byte)
{
        BUG_ON(size & (page_size - 1),
               "check_region_contains_byte expects page multiples");
        BUG_ON((unsigned long)addr & (page_size - 1),
               "check_region_contains_byte expects page alignment");

        memset(page_buffer, byte, page_size);

        unsigned long num_pages = size / page_size;
        unsigned long i;

        // Compare each page checking that it contains our expected byte.
        for (i = 0; i < num_pages; ++i) {
                int ret =
                    memcmp(addr + (i * page_size), page_buffer, page_size);
                if (ret) {
                        return ret;
                }
        }

        return 0;
}

// this test validates that MREMAP_DONTUNMAP moves the pagetables while leaving
// the source mapping mapped.
static void mremap_dontunmap_simple()
{
        unsigned long num_pages = 5;

        void *source_mapping =
            mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
                 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
        BUG_ON(source_mapping == MAP_FAILED, "mmap");

        memset(source_mapping, 'a', num_pages * page_size);

        // Try to just move the whole mapping anywhere (not fixed).
        void *dest_mapping =
            mremap(source_mapping, num_pages * page_size, num_pages * page_size,
                   MREMAP_DONTUNMAP | MREMAP_MAYMOVE, NULL);
        BUG_ON(dest_mapping == MAP_FAILED, "mremap");

        // Validate that the pages have been moved, we know they were moved if
        // the dest_mapping contains a's.
        BUG_ON(check_region_contains_byte
               (dest_mapping, num_pages * page_size, 'a') != 0,
               "pages did not migrate");
        BUG_ON(check_region_contains_byte
               (source_mapping, num_pages * page_size, 0) != 0,
               "source should have no ptes");

        BUG_ON(munmap(dest_mapping, num_pages * page_size) == -1,
               "unable to unmap destination mapping");
        BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
               "unable to unmap source mapping");
}

// This test validates MREMAP_DONTUNMAP will move page tables to a specific
// destination using MREMAP_FIXED, also while validating that the source
// remains intact.
static void mremap_dontunmap_simple_fixed()
{
        unsigned long num_pages = 5;

        // Since we want to guarantee that we can remap to a point, we will
        // create a mapping up front.
        void *dest_mapping =
            mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
                 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
        BUG_ON(dest_mapping == MAP_FAILED, "mmap");
        memset(dest_mapping, 'X', num_pages * page_size);

        void *source_mapping =
            mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
                 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
        BUG_ON(source_mapping == MAP_FAILED, "mmap");
        memset(source_mapping, 'a', num_pages * page_size);

        void *remapped_mapping =
            mremap(source_mapping, num_pages * page_size, num_pages * page_size,
                   MREMAP_FIXED | MREMAP_DONTUNMAP | MREMAP_MAYMOVE,
                   dest_mapping);
        BUG_ON(remapped_mapping == MAP_FAILED, "mremap");
        BUG_ON(remapped_mapping != dest_mapping,
               "mremap should have placed the remapped mapping at dest_mapping");

        // The dest mapping will have been unmap by mremap so we expect the Xs
        // to be gone and replaced with a's.
        BUG_ON(check_region_contains_byte
               (dest_mapping, num_pages * page_size, 'a') != 0,
               "pages did not migrate");

        // And the source mapping will have had its ptes dropped.
        BUG_ON(check_region_contains_byte
               (source_mapping, num_pages * page_size, 0) != 0,
               "source should have no ptes");

        BUG_ON(munmap(dest_mapping, num_pages * page_size) == -1,
               "unable to unmap destination mapping");
        BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
               "unable to unmap source mapping");
}

// This test validates that we can MREMAP_DONTUNMAP for a portion of an
// existing mapping.
static void mremap_dontunmap_partial_mapping()
{
        /*
         *  source mapping:
         *  --------------
         *  | aaaaaaaaaa |
         *  --------------
         *  to become:
         *  --------------
         *  | aaaaa00000 |
         *  --------------
         *  With the destination mapping containing 5 pages of As.
         *  ---------
         *  | aaaaa |
         *  ---------
         */
        unsigned long num_pages = 10;
        void *source_mapping =
            mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
                 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
        BUG_ON(source_mapping == MAP_FAILED, "mmap");
        memset(source_mapping, 'a', num_pages * page_size);

        // We will grab the last 5 pages of the source and move them.
        void *dest_mapping =
            mremap(source_mapping + (5 * page_size), 5 * page_size,
                   5 * page_size,
                   MREMAP_DONTUNMAP | MREMAP_MAYMOVE, NULL);
        BUG_ON(dest_mapping == MAP_FAILED, "mremap");

        // We expect the first 5 pages of the source to contain a's and the
        // final 5 pages to contain zeros.
        BUG_ON(check_region_contains_byte(source_mapping, 5 * page_size, 'a') !=
               0, "first 5 pages of source should have original pages");
        BUG_ON(check_region_contains_byte
               (source_mapping + (5 * page_size), 5 * page_size, 0) != 0,
               "final 5 pages of source should have no ptes");

        // Finally we expect the destination to have 5 pages worth of a's.
        BUG_ON(check_region_contains_byte(dest_mapping, 5 * page_size, 'a') !=
               0, "dest mapping should contain ptes from the source");

        BUG_ON(munmap(dest_mapping, 5 * page_size) == -1,
               "unable to unmap destination mapping");
        BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
               "unable to unmap source mapping");
}

// This test validates that we can remap over only a portion of a mapping.
static void mremap_dontunmap_partial_mapping_overwrite(void)
{
        /*
         *  source mapping:
         *  ---------
         *  |aaaaa|
         *  ---------
         *  dest mapping initially:
         *  -----------
         *  |XXXXXXXXXX|
         *  ------------
         *  Source to become:
         *  ---------
         *  |00000|
         *  ---------
         *  With the destination mapping containing 5 pages of As.
         *  ------------
         *  |aaaaaXXXXX|
         *  ------------
         */
        void *source_mapping =
            mmap(NULL, 5 * page_size, PROT_READ | PROT_WRITE,
                 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
        BUG_ON(source_mapping == MAP_FAILED, "mmap");
        memset(source_mapping, 'a', 5 * page_size);

        void *dest_mapping =
            mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE,
                 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
        BUG_ON(dest_mapping == MAP_FAILED, "mmap");
        memset(dest_mapping, 'X', 10 * page_size);

        // We will grab the last 5 pages of the source and move them.
        void *remapped_mapping =
            mremap(source_mapping, 5 * page_size,
                   5 * page_size,
                   MREMAP_DONTUNMAP | MREMAP_MAYMOVE | MREMAP_FIXED, dest_mapping);
        BUG_ON(dest_mapping == MAP_FAILED, "mremap");
        BUG_ON(dest_mapping != remapped_mapping, "expected to remap to dest_mapping");

        BUG_ON(check_region_contains_byte(source_mapping, 5 * page_size, 0) !=
               0, "first 5 pages of source should have no ptes");

        // Finally we expect the destination to have 5 pages worth of a's.
        BUG_ON(check_region_contains_byte(dest_mapping, 5 * page_size, 'a') != 0,
                        "dest mapping should contain ptes from the source");

        // Finally the last 5 pages shouldn't have been touched.
        BUG_ON(check_region_contains_byte(dest_mapping + (5 * page_size),
                                5 * page_size, 'X') != 0,
                        "dest mapping should have retained the last 5 pages");

        BUG_ON(munmap(dest_mapping, 10 * page_size) == -1,
               "unable to unmap destination mapping");
        BUG_ON(munmap(source_mapping, 5 * page_size) == -1,
               "unable to unmap source mapping");
}

int main(void)
{
        page_size = sysconf(_SC_PAGE_SIZE);

        // test for kernel support for MREMAP_DONTUNMAP skipping the test if
        // not.
        if (kernel_support_for_mremap_dontunmap() != 0) {
                printf("No kernel support for MREMAP_DONTUNMAP\n");
                return KSFT_SKIP;
        }

        // Keep a page sized buffer around for when we need it.
        page_buffer =
            mmap(NULL, page_size, PROT_READ | PROT_WRITE,
                 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
        BUG_ON(page_buffer == MAP_FAILED, "unable to mmap a page.");

        mremap_dontunmap_simple();
        mremap_dontunmap_simple_fixed();
        mremap_dontunmap_partial_mapping();
        mremap_dontunmap_partial_mapping_overwrite();

        BUG_ON(munmap(page_buffer, page_size) == -1,
               "unable to unmap page buffer");

        printf("OK\n");
        return 0;
}