CVE-2023-52920 — bpf: support non-r10 register spill/fill to/from stack in precision tracking

Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

bpf: support non-r10 register spill/fill to/from stack in precision tracking

Use instruction (jump) history to record instructions that performed register spill/fill to/from stack, regardless if this was done through read-only r10 register, or any other register after copying r10 into it *and* potentially adjusting offset.

To make this work reliably, we push extra per-instruction flags into instruction history, encoding stack slot index (spi) and stack frame number in extra 10 bit flags we take away from prev_idx in instruction history. We don't touch idx field for maximum performance, as it's checked most frequently during backtracking.

This change removes basically the last remaining practical limitation of precision backtracking logic in BPF verifier. It fixes known deficiencies, but also opens up new opportunities to reduce number of verified states, explored in the subsequent patches.

There are only three differences in selftests' BPF object files according to veristat, all in the positive direction (less states).

File Program Insns (A) Insns (B) Insns (DIFF) States (A) States (B) States (DIFF) -------------------------------------- ------------- --------- --------- ------------- ---------- ---------- ------------- test_cls_redirect_dynptr.bpf.linked3.o cls_redirect 2987 2864 -123 (-4.12%) 240 231 -9 (-3.75%)…

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CVE-2023-52920 — bpf: support non-r10 register spill/fill to/from stack in precision tracking