From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794372484; b=2kf2hTVXnl6+Pxktyx9g1M3IYcHg0PjuyJR4MpKLuwFNpLATAXnpNTu8V7WTrPwZPx/Z Mpbt69ys+mLHFhDtFKNK3A61JAadrDv46ySWUYdr0EmerGSBU4pwJmLv2GqSUIwpxqEeP 4vJY8hxbAVLsgeCDE4Lsa+JjbxUleExl4dY/qvmGrThgvj4/LM4g01Qkyv5xSYYLC2fUF E9szpr61VxmBK1IBcNyGMx0ssndkNChUd7MZ5EhPMKjrehsiD8/gH7GzlGPr/3dnxSjN6 BFZZvAcbZaqY87C0PNnRMlfe9wDExhCuSS/qbNyxUtnoopxZ5YQnCJvBNiu7OkP439Q== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794372484; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=8oM7hms6BEldF8ERhxE9PfjilLqb4AT4NrzDvUwt/eY=; b=Ybh+nagu2WlAOSjdOjhIKTrW5sABTBrPvh3qzmtJa1iYD7wPjIB7y6qvsp7p1lRZfvlS IcXRtFaMP3JDplSQDjyMPavssR9FpWLITXCf+zgzPnK0b3KvLndTYCERINU9Dgj3fwzLd xv2ro2btjAwymisDwRX2JBHffjJs9+H0vcxGRDJMKUGCJyEGOt2der9WKZZ4122Xd7EKW wyUuIJtxSdGzpGoh/t0N+ZMgA4JHJaDNQrCp6gjhvKbOUQUU5wHHdOCSZIqhKUbiYMHMT bEz/j/0mPlul2ecwKOTbPH6n2YXphZwvVZg5sB8czy+U5O33R/TuaMu3oANdMmhFqeQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=nBCHIiQ7; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0707E606A320 for ; Wed, 11 Nov 2026 04:48:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=nBCHIiQ7 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5C7301F0093C; Wed, 11 Nov 2026 04:48:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794372483; bh=8oM7hms6BEldF8ERhxE9PfjilLqb4AT4NrzDvUwt/eY=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=nBCHIiQ7GVJINOpECaWbyuw3mEFUsNeCTHAkRLpxPqF4bUppSbGnaV/ZUcSTE64d2 0hlY24t5LpluXkYtEiRRfSDsIsn+7+XTViZb+/TEsj+4BkurhJbZI21JfkydlwOiCl eMDfnaNUco6gb4uYwOxFpboIkY7XzHyP+Xu4j7IArIcUt2hWIRWx+SgCaUYz5h5NZu 5IXSHPXRJxc9RwzsGFSfjdmAqUREd638aSNoYUzt7fM4FJTE+yqXn+MMwIqPVJR0jV GhbWAZuojff2ixcjaNgQyytz71MwN9XLWCPbLN1B5s7JnB9Mc0UUQc8xSCJqjjesjc zcHuEIcIVJt5w== From: Sasha Levin To: stable@vger.kernel.org Cc: Qi Xi , Andrew Morton , Zi Yan , Johannes Weiner , Kefeng Wang , Michal Hocko , Nanyong Sun , Suren Baghdasaryan , Vlastimil Babka , Brendan Jackman , Sasha Levin Subject: [PATCH 6.12.y] mm/page_isolation: fix UBSAN shift-out-of-bounds warning Date: Tue, 10 Nov 2026 23:48:01 -0500 Message-ID: <20261111044732.1167229-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261107051923-failed-6.12-eba0e6297edd@kernel.org> References: <20261107051923-failed-6.12-eba0e6297edd@kernel.org> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Qi Xi [ Upstream commit eba0e6297edd60a85bc96ff5cfb734d066af62dd ] Patch series "mm/page_isolation: fix UBSAN shift-out-of-bounds in isolate_single_pageblock", v3. Patch 1 fixes a UBSAN shift-out-of-bounds warning in the PageBuddy branch of isolate_single_pageblock() triggered by concurrent buddy allocation. Patch 2 addresses the same class of issue in the PageCompound branch, where racy compound_order() and compound_head() reads could lead to out-of-range shifts or incorrect page skipping. This patch (of 2): A contig-range allocation racing with buddy allocation on the adjacent pageblock can trigger: UBSAN: shift-out-of-bounds in mm/page_isolation.c:393:15 shift exponent -749042176 is negative Call trace: isolate_single_pageblock start_isolate_page_range alloc_contig_frozen_range_noprof alloc_contig_range_noprof isolate_single_pageblock() first calls set_migratetype_isolate() with zone->lock held, which marks the pageblock MIGRATE_ISOLATE and moves any free page straddling the boundary out of the way. Once the lock is dropped, it scans the MAX_ORDER_NR_PAGES-aligned window [start_pfn, boundary_pfn) locklessly, only to skip the free pages already handled above and to detect in-use pages straddling the boundary. Since this scan only reads page state to decide how far to skip and returns -EBUSY on a straddling in-use page, it does not take the lock. The window also covers the adjacent pageblock, whose free pages stay on the normal movable/CMA freelist and can be allocated concurrently. So after the scan observes PageBuddy(page), another CPU can allocate the page, leaving a stale value in page->private that makes "1 << order" shift out of range. Use buddy_order_unsafe() with READ_ONCE to read the order, and validate it is within MAX_PAGE_ORDER before shifting to prevent UBSAN warnings. Since pageblock_isolate_and_move_free_pages() already handles free pages straddling boundary_pfn under zone->lock, bail out with -EBUSY instead of VM_WARN_ON_ONCE() when a PageBuddy page appears to cross the boundary during the lockless scan. Link: https://lore.kernel.org/20260825120549.966271-2-xiqi2@huawei.com Fixes: b2c9e2fbba32 ("mm: make alloc_contig_range work at pageblock granularity") Signed-off-by: Qi Xi Signed-off-by: Andrew Morton Reviewed-by: Zi Yan Cc: Johannes Weiner Cc: Kefeng Wang Cc: Michal Hocko Cc: Nanyong Sun Cc: Suren Baghdasaryan Cc: Vlastimil Babka Cc: Brendan Jackman Cc: [ sashal: Adjusted the comment to name move_freepages_block_isolate() instead of pageblock_isolate_and_move_free_pages(). ] Signed-off-by: Sasha Levin --- mm/page_isolation.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) diff --git a/mm/page_isolation.c b/mm/page_isolation.c index 6989c5ffd4741..63f9f809ea9f7 100644 --- a/mm/page_isolation.c +++ b/mm/page_isolation.c @@ -376,13 +376,19 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, int flags, } if (PageBuddy(page)) { - int order = buddy_order(page); + unsigned int order = buddy_order_unsafe(page); - /* move_freepages_block_isolate() handled this */ - VM_WARN_ON_ONCE(pfn + (1 << order) > boundary_pfn); - - pfn += 1UL << order; - continue; + /* buddy_order_unsafe() is racy. Validate the order before shifting. */ + if (order <= MAX_PAGE_ORDER && + /* + * move_freepages_block_isolate() splits + * cross-boundary PageBuddy, verify it. + */ + pfn + (1UL << order) <= boundary_pfn) { + pfn += 1UL << order; + continue; + } + goto failed; } /* -- 2.53.0