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Access to memory pointed to by these pointers is done through `BPF_PROBE_{MEM,MEMSX}` instructions and does not produce errors on invalid memory access. This patch set extends `bpf_rdonly_cast()` to allow casts to an equivalent of 'void *', effectively replacing `bpf_probe_read_kernel()` calls in situations where access to individual bytes or integers is necessary. The mechanism was suggested and explored by Andrii Nakryiko in [1]. To help with detecting support for this feature, an `enum bpf_features` is added with intended usage as follows: if (bpf_core_enum_value_exists(enum bpf_features, BPF_FEAT_RDONLY_CAST_TO_VOID)) ... [1] https://github.com/anakryiko/linux/tree/bpf-mem-cast Changelog: v1: https://lore.kernel.org/bpf/20250624191009.902874-1-eddyz87@gmail.com/ v1 -> v2: - renamed BPF_FEAT_TOTAL to __MAX_BPF_FEAT and moved patch introducing bpf_features enum to the start of the series (Alexei); - dropped patch #3 allowing optout from CAP_SYS_ADMIN drop in prog_tests/verifier.c, use a separate runner in prog_tests/* instead. Eduard Zingerman (3): bpf: add bpf_features enum bpf: allow void* cast using bpf_rdonly_cast() selftests/bpf: check operations on untrusted ro pointers to mem kernel/bpf/verifier.c | 79 ++++++++-- .../bpf/prog_tests/mem_rdonly_untrusted.c | 9 ++ .../bpf/progs/mem_rdonly_untrusted.c | 136 ++++++++++++++++++ 3 files changed, 212 insertions(+), 12 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/mem_rdonly_untrusted.c create mode 100644 tools/testing/selftests/bpf/progs/mem_rdonly_untrusted.c -- 2.47.1