On x86-64 calling bpf_get_smp_processor_id() in a kernel with CONFIG_SMP disabled can trigger the following bug, as pcpu_hot is unavailable: [ 8.471774] BUG: unable to handle page fault for address: 00000000936a290c [ 8.471849] #PF: supervisor read access in kernel mode [ 8.471881] #PF: error_code(0x0000) - not-present page Fix by inlining a return 0 in the !CONFIG_SMP case. Fixes: 1ae6921009e5 ("bpf: inline bpf_get_smp_processor_id() helper") Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx> Signed-off-by: Andrea Righi <arighi@xxxxxxxxxx> --- kernel/bpf/verifier.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) ChangeLog v1 -> v2: - inline a "return 0" instead of not inlining bpf_get_smp_processor_id() at all in the !CONFIG_SMP case, as suggested by Daniel diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index f7f892a52a37..761c70899754 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -21281,11 +21281,15 @@ static int do_misc_fixups(struct bpf_verifier_env *env) * changed in some incompatible and hard to support * way, it's fine to back out this inlining logic */ +#ifdef CONFIG_SMP insn_buf[0] = BPF_MOV32_IMM(BPF_REG_0, (u32)(unsigned long)&pcpu_hot.cpu_number); insn_buf[1] = BPF_MOV64_PERCPU_REG(BPF_REG_0, BPF_REG_0); insn_buf[2] = BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_0, 0); cnt = 3; - +#else + BPF_ALU32_REG(BPF_XOR, BPF_REG_0, BPF_REG_0), + cnt = 1; +#endif new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt); if (!new_prog) return -ENOMEM; -- 2.47.1