/ dev / mem的mmap失败,virt_to_phys地址的参数无效,但地址是页面alignment的

出于某种原因,我的mmap失败了一个Invalid argument消息,即使我的偏移是页面alignment。 页面大小是4096字节。 此外CONFIG_STRICT_DEVMEM被禁用,即我可以访问1MB以上的内存。

这是我的代码:

 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; } 

有人可以解释为什么发生这种情况?

编辑

这是我的代码strace

 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 +++ 

Solutions Collecting From Web of "/ dev / mem的mmap失败,virt_to_phys地址的参数无效,但地址是页面alignment的"

nopat内核命令行参数

只需添加它,它的工作原理,如在: https : //stackoverflow.com/a/36634422/895245

这是我的测试设置:

内核模块 :

 #include <asm/io.h> /* virt_to_phys */ #include <linux/debugfs.h> #include <linux/delay.h> /* usleep_range */ #include <linux/kernel.h> #include <linux/kthread.h> #include <linux/module.h> #include <linux/seq_file.h> /* single_open, single_release */ #include <linux/slab.h> /* 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通过: https : //github.com/cirosantilli/linux-kernel-module-cheat/blob/2eca9280e12dbab79ccb67d0640b2a0edc2c9ffc/runqemu#L65

也可以在QEMU显示器上试试xp

devmem2devmem2本身所devmem2 : http : devmem2另请参阅: 从用户空间访问物理地址