Cannot get I/O access to '/dev/mem'
维护者通常 4 天内回复
@demoray 已经在做这个了。
开始于 2026年8月12日。
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描述
Hello. My attempt to get I/O access to '/dev/mem' fails. May the details provided be somehow useful to investigate what prevents it.
$ hostnamectl | sed -n '8p;12p' | awk '$1=$1'
Operating System: Fedora Linux 44 (Workstation Edition)
Kernel: Linux 7.1.7-200.fc44.x86_64
Parameters the kernel was compiled with that are relevant for this report:
$ grep _STRICT_DEVMEM /boot/config-$(uname -r)
CONFIG_STRICT_DEVMEM=y
CONFIG_IO_STRICT_DEVMEM=y
I learned that the main kernel configuration option for controlling I/O access to '/dev/mem' is 'CONFIG_STRICT_DEVMEM'. Lacking knowledge to recompile the kernel, thus my alternative was to add the parameter/key 'strict-devmem=0' to my kernel cmdline:
$ cat /etc/kernel/cmdline
root=UUID=(...) ro rootflags=subvol=root rhgb quiet strict-devmem=0
Test
$ sudo dd if=/dev/mem of=/dev/null
dd: error reading '/dev/mem': Operation not permitted
2048+0 records in
2048+0 records out
1048576 bytes (1.0 MB, 1.0 MiB) copied, 0.0943418 s, 11.1 MB/s
This program
$ file -b avml
ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), static-pie linked, BuildID[sha1]=669c613fbe2bc57310816a6071922ee2203ed86f, stripped
$ stat avml | sed -n '3,4p'
Device: 0,53 Inode: 831989 Links: 1
Access: (0755/-rwxr-xr-x) Uid: (1000/...) Gid: (1000/...)
No permission correlated
$ ./avml acquire --source /dev/mem mem_dump
Error: error: unable to parse /proc/iomem
caused by:
0: need CAP_SYS_ADMIN to read /proc/iomem
Expected!
$ sudo !!
sudo ./avml acquire --source /dev/mem mem_dump
Error: error: unable to read memory
caused by:
0: unable to create memory snapshot from source: /dev/mem
1: unable to create memory snapshot
2: write block failed: 1048576..2483167231
3: io error: unable to read memory page
4: Operation not permitted (os error 1)
I cannot say whether the layout that is presented in 'cat /proc/iomem' represents what is readable within that limit. That seems to me out of topic though.
So, I thought I could expect that the operation would be at last permitted. Since it is not, it's still limited to the first megabyte, which is as expected on a recent Linux kernel. May I ask, do you happen to have a suggestion on this matter?
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