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Merge branch 'bpf-make-kf_trusted_args-default'
Puranjay Mohan says: ==================== bpf: Make KF_TRUSTED_ARGS default v2: https://lore.kernel.org/all/20251231171118.1174007-1-puranjay@kernel.org/ Changes in v2->v3: - Fix documentation: add a new section for kfunc parameters (Eduard) - Remove all occurances of KF_TRUSTED from comments, etc. (Eduard) - Fix the netfilter kfuncs to drop dead NULL checks. - Fix selftest for netfilter kfuncs to check for verification failures and remove the runtime failure that are not possible after this changes v1: https://lore.kernel.org/all/20251224192448.3176531-1-puranjay@kernel.org/ Changes in v1->v2: - Update kfunc_dynptr_param selftest to use a real pointer that is not ptr_to_stack and not CONST_PTR_TO_DYNPTR rather than casting 1 (Alexei) - Thoroughly review all kfuncs in the to find regressions or missing annotations. (Eduard) - Fix kfuncs found from the above step. This series makes trusted arguments the default requirement for all BPF kfuncs, inverting the current opt-in model. Instead of requiring explicit KF_TRUSTED_ARGS flags, kfuncs now require trusted arguments by default and must explicitly opt-out using __nullable/__opt annotations or the KF_RCU flag. This improves security and type safety by preventing BPF programs from passing untrusted or NULL pointers to kernel functions at verification time, while maintaining flexibility for the small number of kfuncs that legitimately need to accept NULL or RCU pointers. MOTIVATION The current opt-in model is error-prone and inconsistent. Most kfuncs already require trusted pointers from sources like KF_ACQUIRE, struct_ops callbacks, or tracepoints. Making trusted arguments the default: - Prevents NULL pointer dereferences at verification time - Reduces defensive NULL checks in kernel code - Provides better error messages for invalid BPF programs - Aligns with existing patterns (context pointers, struct_ops already trusted) IMPACT ANALYSIS Comprehensive analysis of all 304+ kfuncs across 37 kernel files found: - Most kfuncs (299/304) are already safe and require no changes - Only 4 kfuncs required fixes (all included in this series) - 0 regressions found in independent verification All bpf selftests are passing. The hid_bpf tests are also passing: # PASSED: 20 / 20 tests passed. # Totals: pass:20 fail:0 xfail:0 xpass:0 skip:0 error:0 bpf programs in drivers/hid/bpf/progs/ show no regression as shown by veristat: Done. Processed 24 files, 62 programs. Skipped 0 files, 0 programs. TECHNICAL DETAILS The verifier now validates kfunc arguments in this order: 1. NULL check (runs first): Rejects NULL unless parameter has __nullable/__opt 2. Trusted check: Rejects untrusted pointers unless kfunc has KF_RCU Special cases that bypass trusted checking: - Context pointers (xdp_md, __sk_buff): Handled via KF_ARG_PTR_TO_CTX - Struct_ops callbacks: Pre-marked as PTR_TRUSTED during initialization - KF_RCU kfuncs: Have separate validation path for RCU pointers BACKWARD COMPATIBILITY This affects BPF program verification, not runtime: - Valid programs passing trusted pointers: Continue to work - Programs with bugs: May now fail verification (preventing runtime crashes) This series introduces two intentional breaking changes to the BPF verifier's kfunc handling: 1. NULL pointer rejection timing: Kfuncs that previously accepted NULL pointers without KF_TRUSTED_ARGS will now reject NULL at verification time instead of returning runtime errors. This affects netfilter connection tracking functions (bpf_xdp_ct_lookup, bpf_skb_ct_lookup, bpf_xdp_ct_alloc, bpf_skb_ct_alloc), which now enforce their documented "Cannot be NULL" requirements at load time rather than returning -EINVAL at runtime. 2. Fentry/fexit program restrictions: BPF programs using fentry/fexit attachment points can no longer pass their callback arguments directly to kfuncs, as these arguments are not marked as trusted by default. Programs requiring trusted argument semantics should migrate to tp_btf (tracepoint with BTF) attachment points where arguments are guaranteed trusted by the verifier. Both changes strengthen the verifier's safety guarantees by catching errors earlier in the development cycle and are accompanied by comprehensive test updates demonstrating the new expected behaviors. ==================== Link: https://patch.msgid.link/20260102180038.2708325-1-puranjay@kernel.org Signed-off-by:Alexei Starovoitov <ast@kernel.org>