On Mon, 2024-12-16 at 18:24 +0100, Andrea Righi wrote: > On Mon, Dec 16, 2024 at 05:16:33PM +0100, Daniel Borkmann wrote: > > 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; > > That works as well (just tested) and it's probably better since we're > basically inlining the return 0. Do you want me to send a v2 with this? I think both Andrea's and Daniel's versions of the fix are good. Note, however, that I missed one more configuration variable when making bpf_get_smp_processor_id() inlinable: CONFIG_DEBUG_PREEMPT. Helper body: BPF_CALL_0(bpf_get_smp_processor_id) { return smp_processor_id(); } smp_processor_id definition: #ifdef CONFIG_DEBUG_PREEMPT extern unsigned int debug_smp_processor_id(void); # define smp_processor_id() debug_smp_processor_id() #else # define smp_processor_id() __smp_processor_id() #endif Thanks, Eduard.