bpf: verifier: Refactor helper access type tracking

2025-01-17T01:51:10Z

Previously, the verifier was treating all PTR_TO_STACK registers passed to a helper call as potentially written to by the helper. However, all calls to check_stack_range_initialized() already have precise access type information available. Rather than treat ACCESS_HELPER as a proxy for BPF_WRITE, pass enum bpf_access_type to check_stack_range_initialized() to more precisely track helper arguments. One benefit from this precision is that registers tracked as valid spills and passed as a read-only helper argument remain tracked after the call. Rather than being marked STACK_MISC afterwards. An additional benefit is the verifier logs are also more precise. For this particular error, users will enjoy a slightly clearer message. See included selftest updates for examples. Acked-by: Eduard Zingerman Signed-off-by: Daniel Xu Link: https://lore.kernel.org/r/ff885c0e5859e0cd12077c3148ff0754cad4f7ed.1736886479.git.dxu@dxuuu.xyz Signed-off-by: Alexei Starovoitov

selftests/bpf: Tests for uninitialized stack reads

2023-02-22T20:34:50Z

Three testcases to make sure that stack reads from uninitialized locations are accepted by verifier when executed in privileged mode: - read from a fixed offset; - read from a variable offset; - passing a pointer to stack to a helper converts STACK_INVALID to STACK_MISC. Signed-off-by: Eduard Zingerman Acked-by: Andrii Nakryiko Link: https://lore.kernel.org/r/20230219200427.606541-3-eddyz87@gmail.com Signed-off-by: Alexei Starovoitov

kernel/tools/testing/selftests/bpf/progs/uninit_stack.c, branch linux-rolling-stable

bpf: verifier: Refactor helper access type tracking

selftests/bpf: Tests for uninitialized stack reads