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RETBleed Artifact

Demo of leaking /etc/shadow contents on Intel and AMD https://www.youtube.com/watch?v=dmSPvJxPm80

Reverse engineering

  • ./retbleed_zen/pocs/ret_bti finds the patterns that cause BTB collisions.
  • ./retbleed_zen/pocs/cp_bti shows that collisions happen across.
  • ./retbleed_intel/pocs/ret_bti shows that returns go via BTB.
  • ./retbleed_intel/pocs/cp_bti shows that we can train across kernel returns in user space.

Refer to the manuals (AMD, Intel).

  • ./rsb_depth_check shows that there is an RSB that is used. And for Intel, it also indicates that some other prediction mechanism is taking place.
  • ./zen_ras_vs_btb is illustrated in Figure 5. It shows that Return Addres Stack (RAS, aka RSB) is not used on Zen2 when there's a BTB entry. To evaluate Zen/+ BTI_PATTERN must be manualy changed.

Framework

Please refer to section 4.2 of the paper.

  1. Detecting vulnerable returns. We do this with ./ret_finder/funcgraph and ./ret_finder/tools/trace_underfill.py. Refer to the manual.
  2. Identifying exploitable returns. We do this in ./ret_finder/ebpf.
  3. Finding compatible disclosure gadgets. We do this in ./gadget_scanner
  4. Detecting branch history at the victim return. We do this in ./bhb_generate

Evaluation.

Make sure to use an affected system (ref. Table 1).

We evaluate the following:

  1. Leakage rate with ideal gadgets.
  2. Leakage rate with our discovered gadgets
  3. Leaking /etc/shadow

Optimal leakage rate

Requires root and at least 1 huge page enabled. We use ./{retbleed_zen,retbleed_intel}/pocs/eval_bw, which depend on the gadgets in ./{retbleed_zen,retbleed_intel}/pocs/kmod_retbleed_poc. We run eval_bw 11 times and use the median leakage rate and accuracy. To evaluate Zen/+, update PWN_PATTERN in eval_bw.c.

Leakage rate with our discovered gadgets

AMD. Go to ./retbleed_zen/exploits/. To get kernel_text, run ./break_kaslr. Then use the ./do_retbleed.sh.

usage: ./do_retbleed.sh <kernel_text> [core_id=0] [leak_perf]
  unless leak_perf is set (to anything), try to leak /etc/shadow

We run this 100 times and use the median leakage rate and accuracy of the runs that succeeded.

Intel. Go to ./retbleed_intel/exploits/. To get kernel_text, we use MDS, run ./break_kaslr on two threads on the same core. On a 6 core cpu it could be taskset -c 1,7 ./break_kaslr. Then use ./do_retbleed.sh

usage: ./do_retbleed.sh <kernel_text> [core_id=0] [--leak_perf]
  unless --leak_perf is set (to anything), try to leak /etc/shadow

Leaking /etc/shadow

Same as above, but omit the last arg, --leak_perf. As shown in the demos, we can parallelize it to make it go faster.