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利用/proc/pid/pagemap将虚拟地址转换为物理地址
内核文档： Documentation/vm/pagemap.txt
pagemap is a new (as of 2.6.25) set of interfaces in the kernel that allow
userspace programs to examine the page tables and related information by
reading files in /proc.
There are four components to pagemap:
* /proc/pid/pagemap. This file lets a userspace process find out which
physical frame each virtual page is mapped to. It contains one 64-bit
value for each virtual page, containing the following data (from
fs/proc/task_mmu.c, above pagemap_read):
* Bits 0-54 page frame number (PFN) if present
* Bits 0-4 swap type if swapped
* Bits 5-54 swap offset if swapped
* Bit 55 pte is soft-dirty (see Documentation/vm/soft-dirty.txt)
* Bit 56 page exclusively mapped (since 4.2)
* Bits 57-60 zero
* Bit 61 page is file-page or shared-anon (since 3.5)
* Bit 62 page swapped
* Bit 63 page present
Since Linux 4.0 only users with the CAP_SYS_ADMIN capability can get PFNs.
In 4.0 and 4.1 opens by unprivileged fail with -EPERM. Starting from
4.2 the PFN field is zeroed if the user does not have CAP_SYS_ADMIN.
Reason: information about PFNs helps in exploiting Rowhammer vulnerability.
If the page is not present but in swap, then the PFN contains an
encoding of the swap file number and the page‘s offset into the
swap. Unmapped pages return a null PFN. This allows determining
precisely which pages are mapped (or in swap) and comparing mapped
pages between processes.
Efficient users of this interface will use /proc/pid/maps to
determine which areas of memory are actually mapped and llseek to
skip over unmapped regions.
下面是一个工具：
1 #include <stdio.h> 2 #include <stdlib.h> 3 #include <unistd.h> 4 #include <assert.h> 5 #include <errno.h> 6 #include <stdint.h> 7 #include <string.h> 8 9 #define PAGEMAP_ENTRY 810 #define GET_BIT(X,Y) (X & ((uint64_t)1<<Y)) >> Y11 #define GET_PFN(X) X & 0x7FFFFFFFFFFFFF12 13 const int __endian_bit = 1;14 #define is_bigendian() ( (*(char*)&__endian_bit) == 0 )15 16 int i, c, pid, status;17 unsigned long virt_addr; 18 uint64_t read_val, file_offset, page_size;19 char path_buf [0x100] = {};20 FILE * f;21 char *end;22 23 int read_pagemap(char * path_buf, unsigned long virt_addr);24 25 int main(int argc, char ** argv){26 if(argc!=3){27 printf("Argument number is not correct!\n pagemap PID VIRTUAL_ADDRESS\n");28 return -1;29 }30 if(!memcmp(argv[1],"self",sizeof("self"))){31 sprintf(path_buf, "/proc/self/pagemap");32 pid = -1;33 }34 else{35 pid = strtol(argv[1],&end, 10);36 if (end == argv[1] || *end != ‘\0‘ || pid<=0){ 37 printf("PID must be a positive number or ‘self‘\n");38 return -1;39 }40 }41 virt_addr = strtoll(argv[2], NULL, 16);42 if(pid!=-1)43 sprintf(path_buf, "/proc/%u/pagemap", pid);44 45 page_size = getpagesize();46 read_pagemap(path_buf, virt_addr);47 return 0;48 }49 50 int read_pagemap(char * path_buf, unsigned long virt_addr){51 printf("Big endian? %d\n", is_bigendian());52 f = fopen(path_buf, "rb");53 if(!f){54 printf("Error! Cannot open %s\n", path_buf);55 return -1;56 }57 58 //Shifting by virt-addr-offset number of bytes59 //and multiplying by the size of an address (the size of an entry in pagemap file)60 file_offset = virt_addr / page_size * PAGEMAP_ENTRY;61 printf("Vaddr: 0x%lx, Page_size: %lld, Entry_size: %d\n", virt_addr, page_size, PAGEMAP_ENTRY);62 printf("Reading %s at 0x%llx\n", path_buf, (unsigned long long) file_offset);63 status = fseek(f, file_offset, SEEK_SET);64 if(status){65 perror("Failed to do fseek!");66 return -1;67 }68 errno = 0;69 read_val = 0;70 unsigned char c_buf[PAGEMAP_ENTRY];71 for(i=0; i < PAGEMAP_ENTRY; i++){72 c = getc(f);73 if(c==EOF){74 printf("\nReached end of the file\n");75 return 0;76 }77 if(is_bigendian())78 c_buf[i] = c;79 else80 c_buf[PAGEMAP_ENTRY - i - 1] = c;81 printf("[%d]0x%x ", i, c);82 }83 for(i=0; i < PAGEMAP_ENTRY; i++){84 //printf("%d ",c_buf[i]);85 read_val = (read_val << 8) + c_buf[i];86 }87 printf("\n");88 printf("Result: 0x%llx\n", (unsigned long long) read_val);89 if(GET_BIT(read_val, 63)) {90 uint64_t pfn = GET_PFN(read_val);91 printf("PFN: 0x%llx (0x%llx)\n", pfn, pfn * page_size + virt_addr % page_size);92 } else93 printf("Page not present\n");94 if(GET_BIT(read_val, 62))95 printf("Page swapped\n");96 fclose(f);97 return 0;98 }
测试：
用Qemu+vexpress-ca9：
内存： 1GB， 物理地址范围： 0x60000000->0x9FFFFFFF
通过查看/proc/pid/maps获得进程的地址空间的内存映射情况：
1 [root@vexpress ~]# cat /proc/746/maps 2 00008000-001f3000 r-xp 00000000 b3:01 62 /bin/busybox 3 001fa000-001fc000 rw-p 001ea000 b3:01 62 /bin/busybox 4 001fc000-00222000 rw-p 00000000 00:00 0 [heap] 5 b6c7f000-b6c80000 rw-p 00000000 00:00 0 6 b6c80000-b6c8d000 r-xp 00000000 b3:01 174 /lib/libnss_files-2.18.so 7 b6c8d000-b6c94000 ---p 0000d000 b3:01 174 /lib/libnss_files-2.18.so 8 b6c94000-b6c95000 r--p 0000c000 b3:01 174 /lib/libnss_files-2.18.so 9 b6c95000-b6c96000 rw-p 0000d000 b3:01 174 /lib/libnss_files-2.18.so10 b6c96000-b6ca1000 r-xp 00000000 b3:01 141 /lib/libnss_nis-2.18.so11 b6ca1000-b6ca8000 ---p 0000b000 b3:01 141 /lib/libnss_nis-2.18.so12 b6ca8000-b6ca9000 r--p 0000a000 b3:01 141 /lib/libnss_nis-2.18.so13 b6ca9000-b6caa000 rw-p 0000b000 b3:01 141 /lib/libnss_nis-2.18.so14 b6caa000-b6daa000 rw-p 00000000 00:00 0 15 b6daa000-b6dca000 r-xp 00000000 b3:01 129 /lib/ld-2.18.so16 b6dca000-b6dd1000 ---p 00020000 b3:01 129 /lib/ld-2.18.so17 b6dd1000-b6dd2000 r--p 0001f000 b3:01 129 /lib/ld-2.18.so18 b6dd2000-b6dd3000 rw-p 00020000 b3:01 129 /lib/ld-2.18.so19 b6dd3000-b6f06000 r-xp 00000000 b3:01 170 /lib/libc-2.18.so20 b6f06000-b6f0d000 ---p 00133000 b3:01 170 /lib/libc-2.18.so21 b6f0d000-b6f0f000 r--p 00132000 b3:01 170 /lib/libc-2.18.so22 b6f0f000-b6f10000 rw-p 00134000 b3:01 170 /lib/libc-2.18.so23 b6f10000-b6f13000 rw-p 00000000 00:00 0 24 b6f13000-b6f26000 r-xp 00000000 b3:01 177 /lib/libnsl-2.18.so25 b6f26000-b6f2d000 ---p 00013000 b3:01 177 /lib/libnsl-2.18.so26 b6f2d000-b6f2e000 r--p 00012000 b3:01 177 /lib/libnsl-2.18.so27 b6f2e000-b6f2f000 rw-p 00013000 b3:01 177 /lib/libnsl-2.18.so28 b6f2f000-b6f31000 rw-p 00000000 00:00 0 29 b6f31000-b6f39000 r-xp 00000000 b3:01 154 /lib/libnss_compat-2.18.so30 b6f39000-b6f40000 ---p 00008000 b3:01 154 /lib/libnss_compat-2.18.so31 b6f40000-b6f41000 r--p 00007000 b3:01 154 /lib/libnss_compat-2.18.so32 b6f41000-b6f42000 rw-p 00008000 b3:01 154 /lib/libnss_compat-2.18.so33 be958000-be979000 rw-p 00000000 00:00 0 [stack]34 bed04000-bed05000 r-xp 00000000 00:00 0 [sigpage]35 bed05000-bed06000 r--p 00000000 00:00 0 [vvar]36 bed06000-bed07000 r-xp 00000000 00:00 0 [vdso]37 ffff0000-ffff1000 r-xp 00000000 00:00 0 [vectors]
可以看看0x8000这个虚拟地址对应的物理地址：
1 [root@vexpress ~]# ./translate 746 0x80002 Big endian? 03 Vaddr: 0x8000, Page_size: 4096, Entry_size: 84 Reading /proc/746/pagemap at 0x405 [0]0x0 [1]0xf8 [2]0x9 [3]0x0 [4]0x0 [5]0x0 [6]0x0 [7]0xa0 6 Result: 0xa00000000009f8007 PFN: 0x9f800 (0x9f800000)
可以看到， 对应的物理页帧是0x9F800，那么物理地址就是0x9F800000.
下面我们再做一个实验， 进程746的地址空间有一部分用来映射libc：
1 b6dd3000-b6f06000 r-xp 00000000 b3:01 170 /lib/libc-2.18.so2 b6f06000-b6f0d000 ---p 00133000 b3:01 170 /lib/libc-2.18.so3 b6f0d000-b6f0f000 r--p 00132000 b3:01 170 /lib/libc-2.18.so4 b6f0f000-b6f10000 rw-p 00134000 b3:01 170 /lib/libc-2.18.so
此外， 进程835也会用到libc：
1 [root@vexpress ~]# cat /proc/835/maps 2 ... ...3 b6e0b000-b6f3e000 r-xp 00000000 b3:01 170 /lib/libc-2.18.so4 b6f3e000-b6f45000 ---p 00133000 b3:01 170 /lib/libc-2.18.so5 b6f45000-b6f47000 r--p 00132000 b3:01 170 /lib/libc-2.18.so6 b6f47000-b6f48000 rw-p 00134000 b3:01 170 /lib/libc-2.18.so7 ... ...
可以看到， 进程746和835虽然都用了libc，但是对应的虚拟地址却不同，前者是0xb6dd3000， 而后者是0xb6e0b000, 我们知道对于共享库， 在内存只会存在一份， 那么物理地址也就是唯一的， 那么进程746的虚拟地址空间的0xb6dd3000跟进程835的虚拟地址空间的0xb6e0b000对应的物理地址应该是同一个， 下面验证一下：
进程746：
1 [root@vexpress ~]# ./translate 746 0xb6dd30002 virt_addr: 0xb6dd30003 Big endian? 04 Vaddr: 0xb6dd3000, Page_size: 4096, Entry_size: 85 Reading /proc/746/pagemap at 0x5b6e986 [0]0x68 [1]0xfa [2]0x9 [3]0x0 [4]0x0 [5]0x0 [6]0x0 [7]0xa0 7 Result: 0xa00000000009fa688 PFN: 0x9fa68 (0x9fa68000)
可以看到，物理地址是0x9FA68000
进程835：
1 [root@vexpress ~]# ./translate 835 0xb6e0b0002 virt_addr: 0xb6e0b0003 Big endian? 04 Vaddr: 0xb6e0b000, Page_size: 4096, Entry_size: 85 Reading /proc/835/pagemap at 0x5b70586 [0]0x68 [1]0xfa [2]0x9 [3]0x0 [4]0x0 [5]0x0 [6]0x0 [7]0xa0 7 Result: 0xa00000000009fa688 PFN: 0x9fa68 (0x9fa68000)
可以看到， 物理地址也是0x9FA68000， 从而证明了我们的猜想。
完。
利用/proc/pid/pagemap将虚拟地址转换为物理地址