bpf: use reg->var_off instead of reg->off for pointers

2026-02-13T22:41:22+00:00

This commit consolidates static and varying pointer offset tracking logic. All offsets are now represented solely using `.var_off` and min/max fields. The reasons are twofold: - This simplifies pointer tracking code, as each relevant function needs to check the `.var_off` field anyway. - It makes it easier to widen pointer registers for the purpose of loop convergence checks, by forgoing the `regsafe()` logic demanding `.off` fields to be identical. The changes are spread across many functions and are hard to group into smaller patches. Some of the logical changes include: - Checks in __check_ptr_off_reg() are reordered so that the tnum_is_const() check is done before operating on reg->var_off.value. - check_packet_access() now uses check_mem_region_access() to handle possible 'off' overflow cases. - In check_helper_mem_access() utility functions like check_packet_access() are now called with 'off=0', as these utility functions now account for the complete register offset range. - In check_reg_type() a call to __check_ptr_off_reg() is added before a call to btf_struct_ids_match(). This prevents btf_struct_ids_match() from potentially working on non-constant reg->var_off.value. - regsafe() is relaxed to avoid comparing '.off' field for pointers. As a precaution, the changes are verified in [1] by adding a pass checking that no pointer has non-zero '.off' field on each do_check_insn() iteration. [1] https://github.com/eddyz87/bpf/tree/ptrs-off-migration Notable selftests changes: - `.var_off` value changed because it now combines static and varying offsets. Affected tests: - linked_list/incorrect_node_var_off - linked_list/incorrect_head_var_off2 - verifier_align/packet_variable_offset - Overflowing `smax_value` bound leads to a pointer with big negative or positive offset to be rejected immediately (previously overflowing `rX += const` instruction updated `.off` field avoiding the overflow). Affected tests: - verifier_align/dubious_pointer_arithmetic - verifier_bounds/var_off_insn_off_test1 - Invalid access to packet now reports full offset inside a packet. Affected tests: - verifier_direct_packet_access/test23_x_pkt_ptr_4 - A change in check_mem_region_access() behavior: when register `.smin_value` is negative, it reports "rX min value is negative..." before calling into __check_mem_access() which reports "invalid access to ...". In the tests below, the `.off` field was negative, while `.smin_value` remained positive. This is no longer the case after the changes in this commit. Affected tests: - verifier_gotox/jump_table_invalid_mem_acceess_neg - verifier_helper_packet_access/test15_cls_helper_fail_sub - verifier_helper_value_access/imm_out_of_bound_2 - verifier_helper_value_access/reg_out_of_bound_2 - verifier_meta_access/meta_access_test2 - verifier_value_ptr_arith/known_scalar_from_different_maps - lower_oob_arith_test_1 - value_ptr_known_scalar_3 - access_value_ptr_known_scalar - Usage of check_mem_region_access() instead of __check_mem_access() in check_packet_access() changes the reported message from "rX offset is outside ..." to "rX min/max value is outside ...". Affected tests: - verifier_xdp_direct_packet_access/* - In check_func_arg_reg_off() the check for zero offset now operates on `.var_off` field instead of `.off` field. For tests where the pattern looks like `kfunc(reg_with_var_off, ...)`, this changes the reported error: - previously the error "variable ... access ... disallowed" was reported by __check_ptr_off_reg(); - now "R1 must have zero offset ..." is reported by check_func_arg_reg_off() itself. Affected tests: - verifier/calls.c "calls: invalid kfunc call: PTR_TO_BTF_ID with variable offset" Signed-off-by: Eduard Zingerman Link: https://lore.kernel.org/r/20260212-ptrs-off-migration-v2-2-00820e4d3438@gmail.com Signed-off-by: Alexei Starovoitov

selftests/bpf: Add selftest for may_goto

2025-02-15T03:55:15+00:00

Added test cases to ensure that programs with stack sizes exceeding 512 bytes are restricted in non-JITed mode, and can be executed normally in JITed mode, even with stack sizes exceeding 512 bytes due to the presence of may_goto instructions. Test result: echo "0" > /proc/sys/net/core/bpf_jit_enable ./test_progs -t verifier_stack_ptr ... stack size 512 with may_goto with jit:SKIP stack size 512 with may_goto without jit:OK ... Summary: 1/27 PASSED, 25 SKIPPED, 0 FAILED echo "1" > /proc/sys/net/core/bpf_jit_enable ./test_progs -t verifier_stack_ptr ... stack size 512 with may_goto with jit:OK stack size 512 with may_goto without jit:SKIP ... Summary: 1/27 PASSED, 25 SKIPPED, 0 FAILED Signed-off-by: Jiayuan Chen Link: https://lore.kernel.org/r/20250214091823.46042-4-mrpre@163.com Signed-off-by: Alexei Starovoitov

bpf: simplify tnum output if a fully known constant

2023-12-02T19:36:51+00:00

Emit tnum representation as just a constant if all bits are known. Use decimal-vs-hex logic to determine exact format of emitted constant value, just like it's done for register range values. For that move tnum_strn() to kernel/bpf/log.c to reuse decimal-vs-hex determination logic and constants. Acked-by: Shung-Hsi Yu Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/r/20231202175705.885270-12-andrii@kernel.org Signed-off-by: Alexei Starovoitov

selftests/bpf: verifier/stack_ptr.c converted to inline assembly

2023-03-26T00:02:05+00:00

Test verifier/stack_ptr.c automatically converted to use inline assembly. Signed-off-by: Eduard Zingerman Link: https://lore.kernel.org/r/20230325025524.144043-36-eddyz87@gmail.com Signed-off-by: Alexei Starovoitov

kernel/linux.git/tools/testing/selftests/bpf/progs/verifier_stack_ptr.c, branch linux-7.1.y

bpf: use reg->var_off instead of reg->off for pointers

selftests/bpf: Add selftest for may_goto

bpf: simplify tnum output if a fully known constant

selftests/bpf: verifier/stack_ptr.c converted to inline assembly