Created
January 15, 2021 08:35
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Convert virtual address to physical address in user space
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| #define _XOPEN_SOURCE 700 | |
| #include <fcntl.h> /* open */ | |
| #include <stdint.h> /* uint64_t */ | |
| #include <stdio.h> /* printf */ | |
| #include <stdlib.h> /* size_t */ | |
| #include <unistd.h> /* pread, sysconf */ | |
| typedef struct { | |
| uint64_t pfn : 55; | |
| unsigned int soft_dirty : 1; | |
| unsigned int file_page : 1; | |
| unsigned int swapped : 1; | |
| unsigned int present : 1; | |
| } PagemapEntry; | |
| /* Parse the pagemap entry for the given virtual address. | |
| * | |
| * @param[out] entry the parsed entry | |
| * @param[in] pagemap_fd file descriptor to an open /proc/pid/pagemap file | |
| * @param[in] vaddr virtual address to get entry for | |
| * @return 0 for success, 1 for failure | |
| */ | |
| int pagemap_get_entry(PagemapEntry *entry, int pagemap_fd, uintptr_t vaddr) | |
| { | |
| size_t nread; | |
| ssize_t ret; | |
| uint64_t data; | |
| uintptr_t vpn; | |
| vpn = vaddr / sysconf(_SC_PAGE_SIZE); | |
| nread = 0; | |
| while (nread < sizeof(data)) { | |
| ret = pread(pagemap_fd, ((uint8_t*)&data) + nread, sizeof(data) - nread, | |
| vpn * sizeof(data) + nread); | |
| nread += ret; | |
| if (ret <= 0) { | |
| return 1; | |
| } | |
| } | |
| entry->pfn = data & (((uint64_t)1 << 55) - 1); | |
| entry->soft_dirty = (data >> 55) & 1; | |
| entry->file_page = (data >> 61) & 1; | |
| entry->swapped = (data >> 62) & 1; | |
| entry->present = (data >> 63) & 1; | |
| return 0; | |
| } | |
| /* Convert the given virtual address to physical using /proc/PID/pagemap. | |
| * | |
| * @param[out] paddr physical address | |
| * @param[in] pid process to convert for | |
| * @param[in] vaddr virtual address to get entry for | |
| * @return 0 for success, 1 for failure | |
| */ | |
| int virt_to_phys_user(uintptr_t *paddr, pid_t pid, uintptr_t vaddr) | |
| { | |
| char pagemap_file[BUFSIZ]; | |
| int pagemap_fd; | |
| snprintf(pagemap_file, sizeof(pagemap_file), "/proc/%ju/pagemap", (uintmax_t)pid); | |
| pagemap_fd = open(pagemap_file, O_RDONLY); | |
| if (pagemap_fd < 0) { | |
| return 1; | |
| } | |
| PagemapEntry entry; | |
| if (pagemap_get_entry(&entry, pagemap_fd, vaddr)) { | |
| return 1; | |
| } | |
| close(pagemap_fd); | |
| *paddr = (entry.pfn * sysconf(_SC_PAGE_SIZE)) + (vaddr % sysconf(_SC_PAGE_SIZE)); | |
| return 0; | |
| } | |
| int main(int argc, char **argv) | |
| { | |
| pid_t pid; | |
| uintptr_t vaddr, paddr = 0; | |
| if (argc < 3) { | |
| printf("Usage: %s pid vaddr\n", argv[0]); | |
| return EXIT_FAILURE; | |
| } | |
| pid = strtoull(argv[1], NULL, 0); | |
| vaddr = strtoull(argv[2], NULL, 0); | |
| if (virt_to_phys_user(&paddr, pid, vaddr)) { | |
| fprintf(stderr, "error: virt_to_phys_user\n"); | |
| return EXIT_FAILURE; | |
| }; | |
| printf("0x%jx\n", (uintmax_t)paddr); | |
| return EXIT_SUCCESS; | |
| } |
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