mirror of
https://github.com/cirosantilli/linux-kernel-module-cheat.git
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50 lines
1.2 KiB
C
50 lines
1.2 KiB
C
/*
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https://stackoverflow.com/questions/12040303/accessing-physical-address-from-user-space
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Sample call:
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/phys.out 0 16
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Confirm memory from QEMU monitor with:
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xp/0 16
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*/
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#include <fcntl.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <sys/mman.h>
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#include <unistd.h>
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int main(int argc, char *argv[]) {
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if (argc < 3) {
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printf("Usage: %s <phys_addr> <len>\n", argv[0]);
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return 0;
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}
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off_t offset = strtoul(argv[1], NULL, 0);
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size_t len = strtoul(argv[2], NULL, 0);
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size_t pagesize = sysconf(_SC_PAGE_SIZE);
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off_t page_base = (offset / pagesize) * pagesize;
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off_t page_offset = offset - page_base;
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int fd = open("/dev/mem", O_SYNC);
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size_t reallen = page_offset + len;
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unsigned char *mem = mmap(NULL, reallen, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, page_base);
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if (mem == MAP_FAILED) {
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/* TODO why does it fail for some addreses but not for others? */
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perror("mmap");
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exit(EXIT_FAILURE);
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}
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for (size_t i = 0; i < len; ++i) {
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printf("%02x ", (unsigned int)mem[page_offset + i]);
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/* TODO can't edit memory? */
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mem[page_offset + i] = i % 256;
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}
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puts("");
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if (munmap(mem, reallen) == -1) {
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perror("munmap");
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exit(EXIT_FAILURE);
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}
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return EXIT_SUCCESS;
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}
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