From 6668ed271eaefaa63e686bdfbedaeb7b8e492722 Mon Sep 17 00:00:00 2001 From: Kumar Kartikeya Dwivedi Date: Fri, 4 Sep 2026 10:43:19 +0200 Subject: selftests/bpf: Reject graph kptr use after RCU unlock Add a sleepable verifier test that loads a graph-node local kptr in an explicit RCU read-side critical section, then passes its node to bpf_rbtree_remove() after the section ends. Before the verifier fix, the stale NON_OWN_REF flag makes the node look like a live borrowed reference and the program is accepted. After the fix, the pointer is demoted without NON_OWN_REF and the graph kfunc argument is rejected. Also exercise a graph kptr loaded while a spin lock provides implicit RCU protection. The pointer must be invalidated when the lock is released, which guards the required ordering between non-owning-reference invalidation and RCU demotion. Update the existing fault-protected load test state description. The post-unlock pointer no longer carries NON_OWN_REF, but remains readable because the load is rewritten to use BPF_PROBE_MEM. Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com Signed-off-by: Alexei Starovoitov --- fs/verity/pagecache.c | 80 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 80 insertions(+) create mode 100644 fs/verity/pagecache.c (limited to 'fs/verity/pagecache.c') diff --git a/fs/verity/pagecache.c b/fs/verity/pagecache.c new file mode 100644 index 000000000..99f5f53ee --- /dev/null +++ b/fs/verity/pagecache.c @@ -0,0 +1,80 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright 2019 Google LLC + */ +#include "fsverity_private.h" + +#include +#include +#include + +/** + * generic_read_merkle_tree_page - generic ->read_merkle_tree_page helper + * @inode: inode containing the Merkle tree + * @index: 0-based index of the Merkle tree page in the inode + * + * The caller needs to adjust @index from the Merkle-tree relative index passed + * to ->read_merkle_tree_page to the actual index where the Merkle tree is + * stored in the page cache for @inode. + */ +struct page *generic_read_merkle_tree_page(struct inode *inode, pgoff_t index) +{ + struct folio *folio; + + folio = read_mapping_folio(inode->i_mapping, index, NULL); + if (IS_ERR(folio)) + return ERR_CAST(folio); + return folio_file_page(folio, index); +} +EXPORT_SYMBOL_GPL(generic_read_merkle_tree_page); + +/** + * generic_readahead_merkle_tree() - generic ->readahead_merkle_tree helper + * @inode: inode containing the Merkle tree + * @index: 0-based index of the first Merkle tree page to read ahead in the + * inode + * @nr_pages: the number of Merkle tree pages that should be read ahead + * + * The caller needs to adjust @index from the Merkle-tree relative index passed + * to ->read_merkle_tree_page to the actual index where the Merkle tree is + * stored in the page cache for @inode. + */ +void generic_readahead_merkle_tree(struct inode *inode, pgoff_t index, + unsigned long nr_pages) +{ + struct folio *folio; + + lockdep_assert_held(&inode->i_mapping->invalidate_lock); + + folio = __filemap_get_folio(inode->i_mapping, index, FGP_ACCESSED, 0); + if (folio == ERR_PTR(-ENOENT) || + (!IS_ERR(folio) && !folio_test_uptodate(folio))) { + DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index); + + page_cache_ra_unbounded(&ractl, nr_pages, 0); + } + if (!IS_ERR(folio)) + folio_put(folio); +} +EXPORT_SYMBOL_GPL(generic_readahead_merkle_tree); + +/** + * fsverity_fill_zerohash() - fill folio with hashes of zero data block + * @folio: folio to fill + * @offset: offset in the folio to start + * @len: length of the range to fill with hashes + * @vi: fsverity info + */ +void fsverity_fill_zerohash(struct folio *folio, size_t offset, size_t len, + struct fsverity_info *vi) +{ + size_t off = offset; + + WARN_ON_ONCE(!IS_ALIGNED(offset, vi->tree_params.digest_size)); + WARN_ON_ONCE(!IS_ALIGNED(len, vi->tree_params.digest_size)); + + for (; off < (offset + len); off += vi->tree_params.digest_size) + memcpy_to_folio(folio, off, vi->tree_params.zero_digest, + vi->tree_params.digest_size); +} +EXPORT_SYMBOL_GPL(fsverity_fill_zerohash); -- cgit v1.3.1