bpf: copy_verifier_state() should copy 'loop_entry' field

Overview

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

bpf: copy_verifier_state() should copy 'loop_entry' field

The bpf_verifier_state.loop_entry state should be copied by copy_verifier_state(). Otherwise, .loop_entry values from unrelated states would poison env->cur_state.

Additionally, env->stack should not contain any states with .loop_entry != NULL. The states in env->stack are yet to be verified, while .loop_entry is set for states that reached an equivalent state. This means that env->cur_state->loop_entry should always be NULL after pop_stack().

See the selftest in the next commit for an example of the program that is not safe yet is accepted by verifier w/o this fix.

This change has some verification performance impact for selftests:

File Program Insns (A) Insns (B) Insns (DIFF) States (A) States (B) States (DIFF)

arena_htab.bpf.o arena_htab_llvm 717 426 -291 (-40.59%) 57 37 -20 (-35.09%) arena_htab_asm.bpf.o arena_htab_asm 597 445 -152 (-25.46%) 47 37 -10 (-21.28%) arena_list.bpf.o arena_list_del 309 279 -30 (-9.71%) 23 14 -9 (-39.13%) iters.bpf.o iter_subprog_check_stacksafe 155 141 -14 (-9.03%) 15 14 -1 (-6.67%) iters.bpf.o iter_subprog_iters 1094 1003 -91 (-8.32%) 88 83 -5 (-5.68%) iters.bpf.o loop_state_deps2 479 725 +246 (+51.36%) 46 63 +17 (+36.96%) kmem_cache_iter.bpf.o open_coded_iter 63 59 -4 (-6.35%) 7 6 -1 (-14.29%) verifier_bits_iter.bpf.o max_words 92 84 -8 (-8.70%) 8 7 -1 (-12.50%) verifier_iterating_callbacks.bpf.o cond_break2 113 107 -6 (-5.31%) 12 12 +0 (+0.00%)

And significant negative impact for sched_ext:

File Program Insns (A) Insns (B) Insns (DIFF) States (A) States (B) States (DIFF)

bpf.bpf.o lavd_init 7039 14723 +7684 (+109.16%) 490 1139 +649 (+132.45%) bpf.bpf.o layered_dispatch 11485 10548 -937 (-8.16%) 848 762 -86 (-10.14%) bpf.bpf.o layered_dump 7422 1000001 +992579 (+13373.47%) 681 31178 +30497 (+4478.27%) bpf.bpf.o layered_enqueue 16854 71127 +54273 (+322.02%) 1611 6450 +4839 (+300.37%) bpf.bpf.o p2dq_dispatch 665 791 +126 (+18.95%) 68 78 +10 (+14.71%) bpf.bpf.o p2dq_init 2343 2980 +637 (+27.19%) 201 237 +36 (+17.91%) bpf.bpf.o refresh_layer_cpumasks 16487 674760 +658273 (+3992.68%) 1770 65370 +63600 (+3593.22%) bpf.bpf.o rusty_select_cpu 1937 40872 +38935 (+2010.07%) 177 3210 +3033 (+1713.56%) scx_central.bpf.o central_dispatch 636 2687 +2051 (+322.48%) 63 227 +164 (+260.32%) scx_nest.bpf.o nest_init 636 815 +179 (+28.14%) 60 73 +13 (+21.67%) scx_qmap.bpf.o qmap_dispatch
---truncated---

Affected

• Linux >= c8f6d285825f61d619c4c2509bfd75eb366db900 < b7867e55cbcbaed8498b6b96855371eb9afebdc7
• Linux >= 2a0992829ea3864939d917a5c7b48be6629c6217 < 46ba5757a7a4714e7d3f68cfe118208822cb3d78
• Linux >= 2a0992829ea3864939d917a5c7b48be6629c6217 < 8b4afd89fa75f738a80ca849126fd3cad77bcbf1
• Linux >= 2a0992829ea3864939d917a5c7b48be6629c6217 < bbbc02b7445ebfda13e4847f4f1413c6480a85a9
• Linux >= 6.6.15 < 6.6.160
• Linux 6.7

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.