Hi All,

I've a set of questions regarding /dev/mem-

1. Many articles on the net, seem to refer /dev/mem as the gateway to "Physical RAM". But if I am right, /dev/mem is the gateway to the "Physical Address Space" of the processor which might include control registers of many HW peripherals and not just the RAM? Please correct me if I am wrong!

2. In order to prevent attackers from misusing /dev/mem and altering kernel memory, a flag CONFIG_STRICT_DEVMEM needs to be enabled which will prevent user apps from accessing physical address space beyond 1MB. I checked the config file on my PC ( Ubuntu ) and found that CONFIG_STRICT_DEVMEM = y. And I wrote a program which tries to read to physical memory beyond 1 MB and I was able to read!! No segmentation fault or any operation permitted error. How is this possible?
(
My program roughly looks like this-
fd=open ( "/dev/mem", O_RDWR);
ptr=(int*)mmap(0,MAP_SIZE,PROT_READ, fd, myAddress & (~MAP_MASK));
printf("%d",*ptr);
)

Sorry for posting it in "Linux Mobile" forum. I should have posted it in "Linux Kernel" forum. I am unable to find any option to change forum, So I am re-posting it in "Linux Kernel" forum too!

Hello,

Just click the report button on your own post next time and ask a moderator to move it for you. This way you don't have multiple threads for the same question which would only confuse both you and us. Report it now please for closure so you can keep your conversation in one place.

Kind regards,

Eric

Please post your thread in only one forum. Posting a single thread in the most relevant forum will make it easier for members to help you and will keep the discussion in one place. This thread is being closed because it is a duplicate.

Continue here:
http://www.linuxquestions.org/questi...ssions-882771/