125 lines
2.8 KiB
C
125 lines
2.8 KiB
C
#include <stdio.h>
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#include <stdlib.h>
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#include <signal.h>
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#include <sys/mman.h>
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#include "longjmp.h"
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#include "kern_constants.h"
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static jmp_buf buf;
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static void segfault(int sig)
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{
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longjmp(buf, 1);
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}
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static int page_ok(unsigned long page)
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{
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unsigned long *address = (unsigned long *) (page << UM_KERN_PAGE_SHIFT);
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unsigned long n = ~0UL;
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void *mapped = NULL;
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int ok = 0;
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/*
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* First see if the page is readable. If it is, it may still
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* be a VDSO, so we go on to see if it's writable. If not
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* then try mapping memory there. If that fails, then we're
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* still in the kernel area. As a sanity check, we'll fail if
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* the mmap succeeds, but gives us an address different from
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* what we wanted.
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*/
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if (setjmp(buf) == 0)
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n = *address;
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else {
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mapped = mmap(address, UM_KERN_PAGE_SIZE,
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PROT_READ | PROT_WRITE,
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MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
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if (mapped == MAP_FAILED)
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return 0;
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if (mapped != address)
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goto out;
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}
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/*
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* Now, is it writeable? If so, then we're in user address
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* space. If not, then try mprotecting it and try the write
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* again.
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*/
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if (setjmp(buf) == 0) {
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*address = n;
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ok = 1;
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goto out;
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} else if (mprotect(address, UM_KERN_PAGE_SIZE,
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PROT_READ | PROT_WRITE) != 0)
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goto out;
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if (setjmp(buf) == 0) {
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*address = n;
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ok = 1;
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}
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out:
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if (mapped != NULL)
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munmap(mapped, UM_KERN_PAGE_SIZE);
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return ok;
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}
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unsigned long os_get_task_size(void)
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{
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struct sigaction sa, old;
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unsigned long bottom = 0;
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/*
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* A 32-bit UML on a 64-bit host gets confused about the VDSO at
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* 0xffffe000. It is mapped, is readable, can be reprotected writeable
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* and written. However, exec discovers later that it can't be
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* unmapped. So, just set the highest address to be checked to just
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* below it. This might waste some address space on 4G/4G 32-bit
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* hosts, but shouldn't hurt otherwise.
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*/
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unsigned long top = 0xffffd000 >> UM_KERN_PAGE_SHIFT;
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unsigned long test;
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printf("Locating the top of the address space ... ");
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fflush(stdout);
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/*
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* We're going to be longjmping out of the signal handler, so
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* SA_DEFER needs to be set.
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*/
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sa.sa_handler = segfault;
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sigemptyset(&sa.sa_mask);
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sa.sa_flags = SA_NODEFER;
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if (sigaction(SIGSEGV, &sa, &old)) {
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perror("os_get_task_size");
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exit(1);
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}
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if (!page_ok(bottom)) {
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fprintf(stderr, "Address 0x%x no good?\n",
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bottom << UM_KERN_PAGE_SHIFT);
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exit(1);
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}
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/* This could happen with a 4G/4G split */
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if (page_ok(top))
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goto out;
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do {
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test = bottom + (top - bottom) / 2;
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if (page_ok(test))
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bottom = test;
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else
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top = test;
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} while (top - bottom > 1);
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out:
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/* Restore the old SIGSEGV handling */
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if (sigaction(SIGSEGV, &old, NULL)) {
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perror("os_get_task_size");
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exit(1);
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}
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top <<= UM_KERN_PAGE_SHIFT;
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printf("0x%x\n", top);
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return top;
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}
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