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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1783993930; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Zi8sMOqCJW2NCRhuASX5GgkHm8VKvEUdMiR4+SQo7LU=; b=U08nGuagzbVhLLarcP6Ht3kvNTZeXYqu3T5PvbGybt6QkW43Jh4P2dRv0/rY/wJErmKNrS pNZXrhPoV3IehqV6DD/WE8oX+Gf8zyotNtcam06UrfbSuj04VyD/ZiMMyC19BYOCtvHb1H G+APLQqEcI61CRRjWSjiJmTtRPeT/Z4= From: Ye Liu To: Andrew Morton , Vlastimil Babka Cc: Ye Liu , Zi Yan , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v6 8/9] mm/page_owner: clamp skip_buddy_pages() PFN advance at MAX_ORDER_NR_PAGES boundary Date: Tue, 14 Jul 2026 09:51:07 +0800 Message-ID: <20260714015117.78351-9-ye.liu@linux.dev> In-Reply-To: <20260714015117.78351-1-ye.liu@linux.dev> References: <20260714015117.78351-1-ye.liu@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: BE96C140004 X-Stat-Signature: xad1rbj9rx18izjeph1gbu41giwwxgf1 X-HE-Tag: 1783993931-485767 X-HE-Meta: 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 VMPsEO+K RW3/hG86faE33twsBTibXlNgNqs2GVJv+DcVmUYcD+dWu6xgA/aqolv7YXZYsl5NqR9uMsZzRHPCmxTWaC35GIoSkkk68gb2+qo2WTSQfgAghjerlLXhnNk0GsVz9iJO/1ndRTmd0ujMCXPbufNgdVuAPb3g3u/PakAoXF3OmcWdBh3WjW657XXVohzxAGKmozQu3+XDnD74piIlDVwYRgMMaZofU8Ajtc8J0pc5VYip4+huZQYgAqlT6LOfFGONb3o41TnFwkWiOvB/zsQElvZxpud0IeSMxzy/Bcrl0svLKXx8= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: The lockless buddy_order_unsafe() read can return a garbage order value if the page is concurrently allocated between the PageBuddy check and the private read. If this bogus order is <= MAX_PAGE_ORDER, skip_buddy_pages() would arbitrarily advance the PFN, potentially jumping past a MAX_ORDER_NR_PAGES boundary whose pfn_valid() check would have caught an offline memory section. In read_page_owner(), which relies solely on boundary-aligned pfn_valid() to guard pfn_to_page(), skipping the boundary could cause pfn_to_page() to access an unmapped mem_section. Clamp the advance so it never crosses the next MAX_ORDER_NR_PAGES boundary. This is safe for all three callers: the pageblock-iterating ones already handle boundary transitions in their outer loops, and for read_page_owner() the worst case is one extra PageBuddy check per 1024 pages when a bogus order would otherwise push past the boundary. Signed-off-by: Ye Liu Reviewed-by: Zi Yan Reviewed-by: Vlastimil Babka (SUSE) --- mm/page_owner.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/mm/page_owner.c b/mm/page_owner.c index 46a933f9c229..2e3880053a34 100644 --- a/mm/page_owner.c +++ b/mm/page_owner.c @@ -428,6 +428,12 @@ void __folio_copy_owner(struct folio *newfolio, struct folio *old) * to skip less than the full buddy block, but that is acceptable for page owner * iteration purposes. * + * The lockless read of buddy_order_unsafe() can also return a garbage order if + * the page is concurrently allocated and PageBuddy is cleared between the check + * and the read. Clamp the advance at the next MAX_ORDER_NR_PAGES boundary so + * that a bogus order cannot carry @pfn into an unvalidated memory section, + * which would break callers that rely on boundary-aligned pfn_valid() checks. + * * Return: true if the page was skipped (caller should continue its loop), * false if the page is not a buddy page and should be processed normally. */ @@ -439,8 +445,12 @@ static inline bool skip_buddy_pages(unsigned long *pfn, struct page *page) return false; order = buddy_order_unsafe(page); - if (order <= MAX_PAGE_ORDER) - *pfn += (1UL << order) - 1; + if (order <= MAX_PAGE_ORDER) { + unsigned long new_pfn = *pfn + (1UL << order); + unsigned long boundary = ALIGN(*pfn + 1, MAX_ORDER_NR_PAGES); + + *pfn = min(new_pfn, boundary) - 1; + } return true; } -- 2.43.0