libbpf: move arena variables out of the zero page #10319
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The big_alloc1 test in verifier_arena_large assumes that the arena base and the first page allocated by bpf_arena_alloc_pages are identical. This is not the case, because the first page in the arena is populated by global arena data. The test still passes because the code makes the tacit assumption that the first page is on offset PAGE_SIZE instead of 0. Make this distinction explicit in the code, and adjust the page offsets requested during the test to count from the beginning of the arena instead of using the address of the first allocated page. Signed-off-by: Emil Tsalapatis <[email protected]>
Add a stub function for reporting in which offset within a mapping libbpf places the map's data. This will be used in a subsequent patch to support offsetting arena variables within the mapped region. Adjust skeleton generation to account for the new arena memory layout by adding padding corresponding to the offset into the arena map. Add a libbbpf API function to get the data offset within the map's mapping during skeleton generation. Signed-off-by: Emil Tsalapatis <[email protected]>
Currently, libbpf places global arena data at the very beginning of the arena mapping. Stray NULL dereferences into the arena then find valid data and lead to silent corruption instead of causing an arena page fault. The data is placed in the mapping at load time, preventing us from reserving the region using bpf_arena_reserve_pages(). Adjust the arena logic to attempt placing the data from an offset within the arena (currently 16 pages in) instead of the very beginning. If placing the data at an offset would lead to an allocation failure due to global data being as large as the entire arena, progressively reduce the offset down to 0 until placement succeeds. Adjust existing arena tests in the same commit to account for the new global data offset. New tests that explicitly consider the new feature are introduced in the next patch. Signed-off-by: Emil Tsalapatis <[email protected]>
Add tests for the new libbpf globals arena offset logic. The tests cover all three cases: The globals being small enough to be placed at the maximum possible offset, being as large as the arena itself and being placed at the very beginning, and requiring an intermediate offset into the arena. Signed-off-by: Emil Tsalapatis <[email protected]>
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Pull request for series with
subject: libbpf: move arena variables out of the zero page
version: 2
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1024622