On 12/16/24 11:46 AM, Andrea Righi wrote:
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 preventing the inlining of bpf_get_smp_processor_id() when CONFIG_SMP disabled. Fixes: 1ae6921009e5 ("bpf: inline bpf_get_smp_processor_id() helper") Signed-off-by: Andrea Righi <arighi@xxxxxxxxxx>
lgtm, but can't we instead do sth like this : 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; Thanks, Daniel