Messages in this thread | | | Date | Sun, 3 Feb 2019 22:35:44 +0800 | From | Tom Li <> | Subject | Re: [BUG] What is "__ptrval__" in my dmesg logs? Bad "%p" expansion? |
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This is not a bug, rather, this is a security feature that fixes the original behavior, which is now considered an infoleak vul- nerability.
Currently, the address of internal data structures are protected by Kernel Address Space Layout Randomization (KASLR), it forces attackers to bruteforce the location they need to overwrite, thus together with W^X mappings, increases the difficulty of exploiting the kernel. However, showing values of raw pointers will reveal an address of a known internal data structure, allowing an attacker to calculate the location of critical data structure within the kernel, therefore completely defeating the protection by ASLR. This is why disallowing normal users to "dmesg" used to considered a way to improve system security.
As a security measure, the value of "%p" is now hidden by default.
Happy Hacking, Tom Li
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