CVE-2026-23417

Summary

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

bpf: Fix constant blinding for PROBE_MEM32 stores

BPF_ST | BPF_PROBE_MEM32 immediate stores are not handled by bpf_jit_blind_insn(), allowing user-controlled 32-bit immediates to survive unblinded into JIT-compiled native code when bpf_jit_harden >= 1.

The root cause is that convert_ctx_accesses() rewrites BPF_ST|BPF_MEM to BPF_ST|BPF_PROBE_MEM32 for arena pointer stores during verification, before bpf_jit_blind_constants() runs during JIT compilation. The blinding switch only matches BPF_ST|BPF_MEM (mode 0x60), not BPF_ST|BPF_PROBE_MEM32 (mode 0xa0). The instruction falls through unblinded.

Add BPF_ST|BPF_PROBE_MEM32 cases to bpf_jit_blind_insn() alongside the existing BPF_ST|BPF_MEM cases. The blinding transformation is identical: load the blinded immediate into BPF_REG_AX via mov+xor, then convert the immediate store to a register store (BPF_STX).

The rewritten STX instruction must preserve the BPF_PROBE_MEM32 mode so the architecture JIT emits the correct arena addressing (R12-based on x86-64). Cannot use the BPF_STX_MEM() macro here because it hardcodes BPF_MEM mode; construct the instruction directly instead.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/56af722756ed82fee2ae5d5b4d04743407506195
• https://git.kernel.org/stable/c/ccbf29b28b5554f9d65b2fb53b994673ad58b3bf
• https://git.kernel.org/stable/c/de641ea08f8fff6906e169d2576c2ac54e562fbb
• https://git.kernel.org/stable/c/2321a9596d2260310267622e0ad8fbfa6f95378f

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