forked from Minki/linux
113 lines
2.9 KiB
C
113 lines
2.9 KiB
C
|
/*
|
||
|
|
* sysret_ss_attrs.c - test that syscalls return valid hidden SS attributes
|
||
|
|
* Copyright (c) 2015 Andrew Lutomirski
|
||
|
|
*
|
||
|
|
* This program is free software; you can redistribute it and/or modify
|
||
|
|
* it under the terms and conditions of the GNU General Public License,
|
||
|
|
* version 2, as published by the Free Software Foundation.
|
||
|
|
*
|
||
|
|
* This program is distributed in the hope it will be useful, but
|
||
|
|
* WITHOUT ANY WARRANTY; without even the implied warranty of
|
||
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
||
|
|
* General Public License for more details.
|
||
|
|
*
|
||
|
|
* On AMD CPUs, SYSRET can return with a valid SS descriptor with with
|
||
|
|
* the hidden attributes set to an unusable state. Make sure the kernel
|
||
|
|
* doesn't let this happen.
|
||
|
|
*/
|
||
|
|
|
||
|
|
#define _GNU_SOURCE
|
||
|
|
|
||
|
|
#include <stdlib.h>
|
||
|
|
#include <unistd.h>
|
||
|
|
#include <stdio.h>
|
||
|
|
#include <string.h>
|
||
|
|
#include <sys/mman.h>
|
||
|
|
#include <err.h>
|
||
|
|
#include <stddef.h>
|
||
|
|
#include <stdbool.h>
|
||
|
|
#include <pthread.h>
|
||
|
|
|
||
|
|
static void *threadproc(void *ctx)
|
||
|
|
{
|
||
|
|
/*
|
||
|
|
* Do our best to cause sleeps on this CPU to exit the kernel and
|
||
|
|
* re-enter with SS = 0.
|
||
|
|
*/
|
||
|
|
while (true)
|
||
|
|
;
|
||
|
|
|
||
|
|
return NULL;
|
||
|
|
}
|
||
|
|
|
||
|
|
#ifdef __x86_64__
|
||
|
|
extern unsigned long call32_from_64(void *stack, void (*function)(void));
|
||
|
|
|
||
|
|
asm (".pushsection .text\n\t"
|
||
|
|
".code32\n\t"
|
||
|
|
"test_ss:\n\t"
|
||
|
|
"pushl $0\n\t"
|
||
|
|
"popl %eax\n\t"
|
||
|
|
"ret\n\t"
|
||
|
|
".code64");
|
||
|
|
extern void test_ss(void);
|
||
|
|
#endif
|
||
|
|
|
||
|
|
int main()
|
||
|
|
{
|
||
|
|
/*
|
||
|
|
* Start a busy-looping thread on the same CPU we're on.
|
||
|
|
* For simplicity, just stick everything to CPU 0. This will
|
||
|
|
* fail in some containers, but that's probably okay.
|
||
|
|
*/
|
||
|
|
cpu_set_t cpuset;
|
||
|
|
CPU_ZERO(&cpuset);
|
||
|
|
CPU_SET(0, &cpuset);
|
||
|
|
if (sched_setaffinity(0, sizeof(cpuset), &cpuset) != 0)
|
||
|
|
printf("[WARN]\tsched_setaffinity failed\n");
|
||
|
|
|
||
|
|
pthread_t thread;
|
||
|
|
if (pthread_create(&thread, 0, threadproc, 0) != 0)
|
||
|
|
err(1, "pthread_create");
|
||
|
|
|
||
|
|
#ifdef __x86_64__
|
||
|
|
unsigned char *stack32 = mmap(NULL, 4096, PROT_READ | PROT_WRITE,
|
||
|
|
MAP_32BIT | MAP_ANONYMOUS | MAP_PRIVATE,
|
||
|
|
-1, 0);
|
||
|
|
if (stack32 == MAP_FAILED)
|
||
|
|
err(1, "mmap");
|
||
|
|
#endif
|
||
|
|
|
||
|
|
printf("[RUN]\tSyscalls followed by SS validation\n");
|
||
|
|
|
||
|
|
for (int i = 0; i < 1000; i++) {
|
||
|
|
/*
|
||
|
|
* Go to sleep and return using sysret (if we're 64-bit
|
||
|
|
* or we're 32-bit on AMD on a 64-bit kernel). On AMD CPUs,
|
||
|
|
* SYSRET doesn't fix up the cached SS descriptor, so the
|
||
|
|
* kernel needs some kind of workaround to make sure that we
|
||
|
|
* end the system call with a valid stack segment. This
|
||
|
|
* can be a confusing failure because the SS *selector*
|
||
|
|
* is the same regardless.
|
||
|
|
*/
|
||
|
|
usleep(2);
|
||
|
|
|
||
|
|
#ifdef __x86_64__
|
||
|
|
/*
|
||
|
|
* On 32-bit, just doing a syscall through glibc is enough
|
||
|
|
* to cause a crash if our cached SS descriptor is invalid.
|
||
|
|
* On 64-bit, it's not, so try extra hard.
|
||
|
|
*/
|
||
|
|
call32_from_64(stack32 + 4088, test_ss);
|
||
|
|
#endif
|
||
|
|
}
|
||
|
|
|
||
|
|
printf("[OK]\tWe survived\n");
|
||
|
|
|
||
|
|
#ifdef __x86_64__
|
||
|
|
munmap(stack32, 4096);
|
||
|
|
#endif
|
||
|
|
|
||
|
|
return 0;
|
||
|
|
}
|