linux下访问物理地址

hexdump /dev/mem

00fffd0 0000 0000 0000 0000 0000 0000 e800 fe93
00fffe0 00cb 0000 0be9 008c 0000 0000 0000 0000
00ffff0 5bea 00e0 30f0 2f37 3932 312f 0039 d7fc
hexdump: /dev/mem: 不允许的操作
0100000

发现只能访问到1MB的地方。

https://superuser.com/questions/562249/attempting-to-access-ram-dev-mem-says-operation-not-permitted

The linux kernel on your Ubuntu installation ship with a setting^* which limits RAM extraction to has 1 MB.

If you do not wish that you can either recompile the kernel without it (obvious caveeat: you are lowering security!) or you can download and insmod the forensic kernel module fmem to work around this. That provides a /dev/fmem device without any security.

As mentioned by Opello: you can also use strict-devmem=0 in the kernel cmdline.

vim /etc/default/grub

然后更改：

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

至：

GRUB_CMDLINE_LINUX_DEFAULT="iomem=relaxed strict-devmem=0 quiet splash"

Run sudo update-grub

Type reboot




发现修改了没作用，只能编译代码或者hook方式了

CONFIG_STRICT_DEVMEM

试了systemtap方法，虚拟机ubuntu没成功。。。。

https://mp.weixin.qq.com/s?__biz=MzAwMDUwNDgxOA%3D%3D&idx=1&mid=2652666395&scene=21&sn=c200d428c17c32c80fcb13700728931c#wechat_redirect

https://github.com/NateBrune/fmem

devmem2 相关链接：


https://elinux.org/EBC_Exercise_11b_gpio_via_mmap

https://bootlin.com/pub/mirror/devmem2.c