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/*
* Test that VMA updates do not race.
*
* SPDX-License-Identifier: GPL-2.0-or-later
*
* Map a contiguous chunk of RWX memory. Split it into 8 equally sized
* regions, each of which is guaranteed to have a certain combination of
* protection bits set.
*
* Reader, writer and executor threads perform the respective operations on
* pages, which are guaranteed to have the respective protection bit set.
* Two mutator threads change the non-fixed protection bits randomly.
*/
#include <assert.h>
#include <fcntl.h>
#include <pthread.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <sys/mman.h>
#include <unistd.h>
#include "nop_func.h"
#define PAGE_IDX_BITS 10
#define PAGE_COUNT (1 << PAGE_IDX_BITS)
#define PAGE_IDX_MASK (PAGE_COUNT - 1)
#define REGION_IDX_BITS 3
#define PAGE_IDX_R_MASK (1 << 7)
#define PAGE_IDX_W_MASK (1 << 8)
#define PAGE_IDX_X_MASK (1 << 9)
#define REGION_MASK (PAGE_IDX_R_MASK | PAGE_IDX_W_MASK | PAGE_IDX_X_MASK)
#define PAGES_PER_REGION (1 << (PAGE_IDX_BITS - REGION_IDX_BITS))
struct context {
int pagesize;
char *ptr;
int dev_null_fd;
volatile int mutator_count;
};
static void *thread_read(void *arg)
{
struct context *ctx = arg;
ssize_t sret;
size_t i, j;
int ret;
for (i = 0; ctx->mutator_count; i++) {
char *p;
j = (i & PAGE_IDX_MASK) | PAGE_IDX_R_MASK;
p = &ctx->ptr[j * ctx->pagesize];
/* Read directly. */
ret = memcmp(p, nop_func, sizeof(nop_func));
if (ret != 0) {
fprintf(stderr, "fail direct read %p\n", p);
abort();
}
/* Read indirectly. */
sret = write(ctx->dev_null_fd, p, 1);
if (sret != 1) {
if (sret < 0) {
fprintf(stderr, "fail indirect read %p (%m)\n", p);
} else {
fprintf(stderr, "fail indirect read %p (%zd)\n", p, sret);
}
abort();
}
}
return NULL;
}
static void *thread_write(void *arg)
{
struct context *ctx = arg;
struct timespec *ts;
size_t i, j;
int ret;
for (i = 0; ctx->mutator_count; i++) {
j = (i & PAGE_IDX_MASK) | PAGE_IDX_W_MASK;
/* Write directly. */
memcpy(&ctx->ptr[j * ctx->pagesize], nop_func, sizeof(nop_func));
/* Write using a syscall. */
ts = (struct timespec *)(&ctx->ptr[(j + 1) * ctx->pagesize] -
sizeof(struct timespec));
ret = clock_gettime(CLOCK_REALTIME, ts);
if (ret != 0) {
fprintf(stderr, "fail indirect write %p (%m)\n", ts);
abort();
}
}
return NULL;
}
static void *thread_execute(void *arg)
{
struct context *ctx = arg;
size_t i, j;
for (i = 0; ctx->mutator_count; i++) {
j = (i & PAGE_IDX_MASK) | PAGE_IDX_X_MASK;
((void(*)(void))&ctx->ptr[j * ctx->pagesize])();
}
return NULL;
}
static void *thread_mutate(void *arg)
{
size_t i, start_idx, end_idx, page_idx, tmp;
struct context *ctx = arg;
unsigned int seed;
int prot, ret;
seed = (unsigned int)time(NULL);
for (i = 0; i < 10000; i++) {
start_idx = rand_r(&seed) & PAGE_IDX_MASK;
end_idx = rand_r(&seed) & PAGE_IDX_MASK;
if (start_idx > end_idx) {
tmp = start_idx;
start_idx = end_idx;
end_idx = tmp;
}
prot = rand_r(&seed) & (PROT_READ | PROT_WRITE | PROT_EXEC);
for (page_idx = start_idx & REGION_MASK; page_idx <= end_idx;
page_idx += PAGES_PER_REGION) {
if (page_idx & PAGE_IDX_R_MASK) {
prot |= PROT_READ;
}
if (page_idx & PAGE_IDX_W_MASK) {
/* FIXME: qemu syscalls check for both read+write. */
prot |= PROT_WRITE | PROT_READ;
}
if (page_idx & PAGE_IDX_X_MASK) {
prot |= PROT_EXEC;
}
}
ret = mprotect(&ctx->ptr[start_idx * ctx->pagesize],
(end_idx - start_idx + 1) * ctx->pagesize, prot);
assert(ret == 0);
}
__atomic_fetch_sub(&ctx->mutator_count, 1, __ATOMIC_SEQ_CST);
return NULL;
}
int main(void)
{
pthread_t threads[5];
struct context ctx;
size_t i;
int ret;
/* Without a template, nothing to test. */
if (sizeof(nop_func) == 0) {
return EXIT_SUCCESS;
}
/* Initialize memory chunk. */
ctx.pagesize = getpagesize();
ctx.ptr = mmap(NULL, PAGE_COUNT * ctx.pagesize,
PROT_READ | PROT_WRITE | PROT_EXEC,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
assert(ctx.ptr != MAP_FAILED);
for (i = 0; i < PAGE_COUNT; i++) {
memcpy(&ctx.ptr[i * ctx.pagesize], nop_func, sizeof(nop_func));
}
ctx.dev_null_fd = open("/dev/null", O_WRONLY);
assert(ctx.dev_null_fd >= 0);
ctx.mutator_count = 2;
/* Start threads. */
ret = pthread_create(&threads[0], NULL, thread_read, &ctx);
assert(ret == 0);
ret = pthread_create(&threads[1], NULL, thread_write, &ctx);
assert(ret == 0);
ret = pthread_create(&threads[2], NULL, thread_execute, &ctx);
assert(ret == 0);
for (i = 3; i <= 4; i++) {
ret = pthread_create(&threads[i], NULL, thread_mutate, &ctx);
assert(ret == 0);
}
/* Wait for threads to stop. */
for (i = 0; i < sizeof(threads) / sizeof(threads[0]); i++) {
ret = pthread_join(threads[i], NULL);
assert(ret == 0);
}
/* Destroy memory chunk. */
ret = close(ctx.dev_null_fd);
assert(ret == 0);
ret = munmap(ctx.ptr, PAGE_COUNT * ctx.pagesize);
assert(ret == 0);
return EXIT_SUCCESS;
}
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