I made a video about how hardened malloc can help secure against very simple heap overflows. If you have time, I'd be happy if you could review the video and tell me where I made mistakes, and what more I can learn about libhardened_malloc.
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One thing to note is that when canaries are enabled (which is the default), they add 8 bytes to the size of allocation requests, so some allocations are pushed into a higher size class, which needs to be taken into account when checking the table to determine the size class.
The offset test prints the measured offset between different size classes and has to take canaries into account: github.com/GrapheneOS/har. It's a useful way of demonstrating the isolated regions for each size class and randomization of the guard regions and slab slot selection.
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To test the randomization, you can run the offset test multiple times and compare the results across runs. Also worth noting there's a `preload.sh` script to handle that for you when testing with dynamically linked executables not linked with libhardened_malloc.so.
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