bpf: Restrict CO-RE poisoning to relocatable instructions

Overview

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

bpf: Restrict CO-RE poisoning to relocatable instructions

CO-RE relocation records can name any instruction offset. When a relocation cannot be resolved, bpf_core_patch_insn() currently poisons its target before checking whether that instruction is a valid relocation target. Malformed metadata can therefore replace jumps, calls, exits, register-source arithmetic, or non-immediate loads instead of failing at the relocation step.

Handle poisoning only after the instruction has passed the same class and operand-form checks used for a resolved relocation. Route invalid forms through the existing diagnostic and return a hard error. Keep poisoning supported instructions, including both halves of a plain ldimm64, so an unresolved relocation in dead code remains valid.

Extend bpf_core_poison_insn() to poison both halves of ldimm64, and return its status directly from each validated instruction case. This avoids routing the success path through a common label and leaves the helper free to report errors.

The shared relocation code applies this restriction to both libbpf and in-kernel CO-RE.

Affected

• Linux >= d7a252708dbc950ca2064310217e8b9f85846e2f < a8c47e62d9aea2d47a09e06c1682c59c21b92449
• Linux >= d7a252708dbc950ca2064310217e8b9f85846e2f < d3219c229d16900cef936adad28633c98946e432
• Linux >= d7a252708dbc950ca2064310217e8b9f85846e2f < a0b79cdfcf34b53c85bac2d3cf022fc1342eeca0
• Linux >= d7a252708dbc950ca2064310217e8b9f85846e2f < f2a24101e89dd0804e717da7c1bd6af513698aa2
• Linux >= d7a252708dbc950ca2064310217e8b9f85846e2f < 2d7d04357c41aa49a5ac658fcc207439f2ad6456
• Linux >= d7a252708dbc950ca2064310217e8b9f85846e2f < 8e4cbcca1e0a2fc5e6c8edb68e0cf5f2587f9319
• Linux >= d7a252708dbc950ca2064310217e8b9f85846e2f < 394ae398337c5f87e567f6cd63b937fc2b2f6ddc
• Linux 5.6

Remediation

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