问题:

For some reason my mmap failed with an Invalid argument message even though my offset is page aligned. Page size is 4096 bytes. Also CONFIG_STRICT_DEVMEM is disabled, i.e. I can access memory above 1MB.

Here is my code:

void *mmap64; off_t offset = 0x000000d9fcc000; int memFd = open("/dev/mem", O_RDWR); if (-1 == memFd)   perror("Error ");  mmap64 = mmap(0, getpagesize(), PROT_WRITE | PROT_READ, MAP_SHARED, memFd, offset); if (MAP_FAILED == mmap64) {   perror("Error ");   return -1; }

Can someone explain why this is happening?

EDIT

Here is the strace of my code

execve("./to_phys_test", ["./to_phys_test", "-r"], [/* 18 vars */]) = 0 brk(0)                                  = 0x2012000 access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory) mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe240a2c000 access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory) open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3 fstat(3, {st_mode=S_IFREG|0644, st_size=162063, ...}) = 0 mmap(NULL, 162063, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fe240a04000 close(3)                                = 0 access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory) open("/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0P \2\0\0\0\0\0"..., 832) = 832 fstat(3, {st_mode=S_IFREG|0755, st_size=1840928, ...}) = 0 mmap(NULL, 3949248, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fe240447000 mprotect(0x7fe240601000, 2097152, PROT_NONE) = 0 mmap(0x7fe240801000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1ba000) = 0x7fe240801000 mmap(0x7fe240807000, 17088, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fe240807000 close(3)                                = 0 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe240a03000 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe240a01000 arch_prctl(ARCH_SET_FS, 0x7fe240a01740) = 0 mprotect(0x7fe240801000, 16384, PROT_READ) = 0 mprotect(0x601000, 4096, PROT_READ)     = 0 mprotect(0x7fe240a2e000, 4096, PROT_READ) = 0 munmap(0x7fe240a04000, 162063)          = 0 open("/dev/mem", O_RDWR)                = 3 open("/dev/my_kmodule", O_RDWR)    = 4 ioctl(4, 0x40086e00, 0x7ffc72b334b0)    = 0 fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 0), ...}) = 0 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe240a2b000 write(1, "sa.size = 44\n", 13)          = 13 write(1, "sa.addr_uint64_t = d9047000\n", 28) = 28 write(1, "sa.addr_void_ptr = 0xd9047000\n", 30) = 30 write(1, "PAGE_SIZE = 4096\n", 17)      = 17 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, 3, 0xd9047000) = -1 EINVAL (Invalid argument) dup(2)                                  = 5 fcntl(5, F_GETFL)                       = 0x8002 (flags O_RDWR|O_LARGEFILE) brk(0)                                  = 0x2012000 brk(0x2033000)                          = 0x2033000 fstat(5, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 0), ...}) = 0 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe240a2a000 lseek(5, 0, SEEK_CUR)                   = -1 ESPIPE (Illegal seek) write(5, "Error : Invalid argument\n", 25) = 25 close(5)                                = 0 munmap(0x7fe240a2a000, 4096)            = 0 exit_group(-1)                          = ? +++ exited with 255 +++

回答1:

nopat kernel command line argument

Just add that and it works, as mentioned at: https://stackoverflow.com/a/36634422/895245

Here is my test setup:

kernel module:

#include  /* virt_to_phys */ #include  #include  /* usleep_range */ #include  #include  #include  #include  /* single_open, single_release */ #include  /* kmalloc, kfree */  static volatile u32 *i;  static struct dentry *debugfs_file;  static int show(struct seq_file *m, void *v) {     seq_printf(m,         "*i 0x%llx\n"         "i %p\n"         "virt_to_phys 0x%llx\n",         (unsigned long long)*i,         i,         (unsigned long long)virt_to_phys((void *)i)     );     return 0; }  static int open(struct inode *inode, struct  file *file) {     return single_open(file, show, NULL); }  static const struct file_operations fops = {     .llseek = seq_lseek,     .open = open,     .owner = THIS_MODULE,     .read = seq_read,     .release = single_release, };  static int myinit(void) {     i = kmalloc(sizeof(i), GFP_KERNEL);     *i = 0x12345678;     debugfs_file = debugfs_create_file(         "lkmc_virt_to_phys", S_IRUSR, NULL, NULL, &fops);     return 0; }  static void myexit(void) {     debugfs_remove(debugfs_file);     kfree((void *)i); }  module_init(myinit) module_exit(myexit) MODULE_LICENSE("GPL");

/dev/mem userland:

#!/bin/sh set -ex insmod /virt_to_phys.ko cd /sys/kernel/debug cat lkmc_virt_to_phys # *i = 0x12345678 addr=$(grep virt_to_phys lkmc_virt_to_phys | cut -d ' ' -f 2) devmem2 "$addr" devmem2 "$addr" w 0x9ABCDEF0 cat lkmc_virt_to_phys # *i = 0x9ABCDEF0 rmmod virt_to_phys

nopat being passed at: https://github.com/cirosantilli/linux-kernel-module-cheat/blob/2eca9280e12dbab79ccb67d0640b2a0edc2c9ffc/runqemu#L65

Also try xp on QEMU monitor.

And devmem2 is upstreamed by Buildroot itself: http://free-electrons.com/pub/mirror/devmem2.c See also: Accessing physical address from user space

转载请标明出处:mmap of /dev/mem fails with invalid argument for virt_to_phys address, but address is page aligned

文章来源: mmap of /dev/mem fails with invalid argument for virt_to_phys address, but address is page aligned

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