In the Linux kernel, the following vulnerability has been resolved: bpf: Disallow interpreter fallback for BPF_ADDR_PERCPU insn The BPF_MOV64_PERCPU_REG insn requires JIT to emit native code to for 'dst_reg = src_reg + <percpu_base_off…

Overview

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

bpf: Disallow interpreter fallback for BPF_ADDR_PERCPU insn

The BPF_MOV64_PERCPU_REG insn requires JIT to emit native code to for 'dst_reg = src_reg + <percpu_base_off>'.

However, the interpreter ignores the 'off' at its ALU64_MOV_X label. The 'off' indicates the insn is BPF_MOV64_PERCPU_REG insn. Then, when the interpreter loads memory from the register, it will hit a page fault.

[ 2.545572] BUG: unable to handle page fault for address: ffffffffacaaf034 [ 2.546485] #PF: supervisor read access in kernel mode [ 2.547167] #PF: error_code(0x0000) - not-present page [ 2.547850] PGD 134e63067 P4D 134e63067 PUD 134e64063 PMD 10021c063 PTE 800ffffeca550062 [ 2.548912] Oops: Oops: 0000 [#1] SMP PTI

Set jit_required as true in order to disallow interpreter fallback in core.c::__bpf_prog_select_runtime(), if any BPF_ADDR_PERCPU insn is patched to the prog.

BTW, rename the helper bpf_map_supports_cpu_flags() to bpf_map_is_percpu_map().

Remediation

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