LoongArch: BPF: Don't override subprog's return value

Overview

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

LoongArch: BPF: Don't override subprog's return value

The verifier test calls: div by 0 in subprog triggers a panic at the ld.bu instruction. The ld.bu insn is trying to load byte from memory address returned by the subprog. The subprog actually set the correct address at the a5 register (dedicated register for BPF return values). But at commit 73c359d1d356 ("LoongArch: BPF: Sign-extend return values") we also sign extended a5 to the a0 register (return value in LoongArch). For function call insn, we later propagate the a0 register back to a5 register. This is right for native calls but wrong for bpf2bpf calls which expect zero-extended return value in a5 register. So only move a0 to a5 for native calls (i.e. non-BPF_PSEUDO_CALL).

Affected

• Linux >= 8382e92f90b601acf6d426121e6f4991502e767d < d99845f672cce0b610f7c51248ef95d7df63927e
• Linux >= 0c8d50501bc13cacecc19caaddc10db372592a39 < 7df2696256a034405d3c5a71b3a4c54725de4404
• Linux >= d5d83242a1d778ceb6d8b07c6b491cf7483ca112 < 223d565d8892481684091cfbaf3466f2b0e289d3
• Linux >= 73c359d1d356cf10236ccd358bd55edab33e9424 < 780628a780b622759d9e5adc76d15432144da1a3
• Linux >= 73c359d1d356cf10236ccd358bd55edab33e9424 < 996e90ab446641553e8e21707b38b9709605e0e0
• Linux >= 73c359d1d356cf10236ccd358bd55edab33e9424 < 60f3caff1492e5b8616b9578c4bedb5c0a88ed14
• Linux 3b75f627b73d96787a493e2f1187543ba9c056a4
• Linux >= 6.1.120 < 6.1.191
• Linux >= 6.6.64 < 6.6.87
• Linux >= 6.12.2 < 6.12.23
• Linux >= 6.11.11 < 6.12
• Linux 6.13

Remediation

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