ghsa-79p2-24v8-gp9v
Vulnerability from github
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%) xdp_synproxy_kern.bpf.linked3.o syncookie_tc 82848 82661 -187 (-0.23%) 5107 5073 -34 (-0.67%) xdp_synproxy_kern.bpf.linked3.o syncookie_xdp 85116 84964 -152 (-0.18%) 5162 5130 -32 (-0.62%)
Note, I avoided renaming jmp_history to more generic insn_hist to minimize number of lines changed and potential merge conflicts between bpf and bpf-next trees.
Notice also cur_hist_entry pointer reset to NULL at the beginning of instruction verification loop. This pointer avoids the problem of relying on last jump history entry's insn_idx to determine whether we already have entry for current instruction or not. It can happen that we added jump history entry because current instruction is_jmp_point(), but also we need to add instruction flags for stack access. In this case, we don't want to entries, so we need to reuse last added entry, if it is present.
Relying on insn_idx comparison has the same ambiguity problem as the one that was fixed recently in [0], so we avoid that.
[0] https://patchwork.kernel.org/project/netdevbpf/patch/20231110002638.4168352-3-andrii@kernel.org/
{
"affected": [],
"aliases": [
"CVE-2023-52920"
],
"database_specific": {
"cwe_ids": [
"CWE-476"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-11-05T10:15:24Z",
"severity": "MODERATE"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: support non-r10 register spill/fill to/from stack in precision tracking\n\nUse instruction (jump) history to record instructions that performed\nregister spill/fill to/from stack, regardless if this was done through\nread-only r10 register, or any other register after copying r10 into it\n*and* potentially adjusting offset.\n\nTo make this work reliably, we push extra per-instruction flags into\ninstruction history, encoding stack slot index (spi) and stack frame\nnumber in extra 10 bit flags we take away from prev_idx in instruction\nhistory. We don\u0027t touch idx field for maximum performance, as it\u0027s\nchecked most frequently during backtracking.\n\nThis change removes basically the last remaining practical limitation of\nprecision backtracking logic in BPF verifier. It fixes known\ndeficiencies, but also opens up new opportunities to reduce number of\nverified states, explored in the subsequent patches.\n\nThere are only three differences in selftests\u0027 BPF object files\naccording to veristat, all in the positive direction (less states).\n\nFile Program Insns (A) Insns (B) Insns (DIFF) States (A) States (B) States (DIFF)\n-------------------------------------- ------------- --------- --------- ------------- ---------- ---------- -------------\ntest_cls_redirect_dynptr.bpf.linked3.o cls_redirect 2987 2864 -123 (-4.12%) 240 231 -9 (-3.75%)\nxdp_synproxy_kern.bpf.linked3.o syncookie_tc 82848 82661 -187 (-0.23%) 5107 5073 -34 (-0.67%)\nxdp_synproxy_kern.bpf.linked3.o syncookie_xdp 85116 84964 -152 (-0.18%) 5162 5130 -32 (-0.62%)\n\nNote, I avoided renaming jmp_history to more generic insn_hist to\nminimize number of lines changed and potential merge conflicts between\nbpf and bpf-next trees.\n\nNotice also cur_hist_entry pointer reset to NULL at the beginning of\ninstruction verification loop. This pointer avoids the problem of\nrelying on last jump history entry\u0027s insn_idx to determine whether we\nalready have entry for current instruction or not. It can happen that we\nadded jump history entry because current instruction is_jmp_point(), but\nalso we need to add instruction flags for stack access. In this case, we\ndon\u0027t want to entries, so we need to reuse last added entry, if it is\npresent.\n\nRelying on insn_idx comparison has the same ambiguity problem as the one\nthat was fixed recently in [0], so we avoid that.\n\n [0] https://patchwork.kernel.org/project/netdevbpf/patch/20231110002638.4168352-3-andrii@kernel.org/",
"id": "GHSA-79p2-24v8-gp9v",
"modified": "2024-11-07T21:31:43Z",
"published": "2024-11-05T12:31:03Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2023-52920"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/41f6f64e6999a837048b1bd13a2f8742964eca6b"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
Sightings
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