Messages in this thread | | | From | Menglong Dong <> | Subject | [PATCH net-next v2 0/2] bpf: support to trace BPF_JNE | Date | Tue, 12 Dec 2023 21:10:29 +0800 |
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For now, the reg bounds is not handled for BPF_JNE case, which can cause the failure of following case:
/* The type of "a" is u16 */ if (a > 0 && a < 100) { /* the range of the register for a is [0, 99], not [1, 99], * and will cause the following error: * * invalid zero-sized read * * as a can be 0. */ bpf_skb_store_bytes(skb, xx, xx, a, 0); }
In the code above, "a > 0" will be compiled to "jmp xxx if a == 0". In the TRUE branch, the dst_reg will be marked as known to 0. However, in the fallthrough(FALSE) branch, the dst_reg will not be handled, which makes the [min, max] for a is [0, 99], not [1, 99].
In the 1st patch, we reduce the range of the dst reg if the src reg is a const and is exactly the edge of the dst reg For BPF_JNE.
In the 2nd patch, we just activate the test case for this logic in range_cond(), which is committed by Andrii in the commit 8863238993e2 ("selftests/bpf: BPF register range bounds tester").
Changes since v1: - simplify the code in the 1st patch - introduce the 2nd patch for the testing
Menglong Dong (2): bpf: make the verifier trace the "not qeual" for regs selftests/bpf: activate the OP_NE login in range_cond()
kernel/bpf/verifier.c | 29 ++++++++++++++++++- .../selftests/bpf/prog_tests/reg_bounds.c | 7 +---- 2 files changed, 29 insertions(+), 7 deletions(-)
-- 2.39.2
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