The patch titled Subject: smaps: fix crash in smaps_hugetlb_range for non-present hugetlb entries has been added to the -mm mm-hotfixes-unstable branch. Its filename is smaps-fix-crash-in-smaps_hugetlb_range-for-non-present-hugetlb-entries.patch
This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...
This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days
------------------------------------------------------ From: Ming Wang wangming01@loongson.cn Subject: smaps: fix crash in smaps_hugetlb_range for non-present hugetlb entries Date: Wed, 23 Apr 2025 09:03:59 +0800
When reading /proc/pid/smaps for a process that has mapped a hugetlbfs file with MAP_PRIVATE, the kernel might crash inside pfn_swap_entry_to_page. This occurs on LoongArch under specific conditions.
The root cause involves several steps:
1. When the hugetlbfs file is mapped (MAP_PRIVATE), the initial PMD (or relevant level) entry is often populated by the kernel during mmap() with a non-present entry pointing to the architecture's invalid_pte_table On the affected LoongArch system, this address was observed to be 0x90000000031e4000.
2. The smaps walker (walk_hugetlb_range -> smaps_hugetlb_range) reads this entry.
3. The generic is_swap_pte() macro checks `!pte_present() && !pte_none()`. The entry (invalid_pte_table address) is not present. Crucially, the generic pte_none() check (`!(pte_val(pte) & ~_PAGE_GLOBAL)`) returns false because the invalid_pte_table address is non-zero. Therefore, is_swap_pte() incorrectly returns true.
4. The code enters the `else if (is_swap_pte(...))` block.
5. Inside this block, it checks `is_pfn_swap_entry()`. Due to a bit pattern coincidence in the invalid_pte_table address on LoongArch, the embedded generic `is_migration_entry()` check happens to return true (misinterpreting parts of the address as a migration type).
6. This leads to a call to pfn_swap_entry_to_page() with the bogus swap entry derived from the invalid table address.
7. pfn_swap_entry_to_page() extracts a meaningless PFN, finds an unrelated struct page, checks its lock status (unlocked), and hits the `BUG_ON(is_migration_entry(entry) && !PageLocked(p))` assertion.
The original code's intent in the `else if` block seems aimed at handling potential migration entries, as indicated by the inner `is_pfn_swap_entry()` check. The issue arises because the outer `is_swap_pte()` check incorrectly includes the invalid table pointer case on LoongArch.
This patch fixes the issue by changing the condition in smaps_hugetlb_range() from the broad `is_swap_pte()` to the specific `is_hugetlb_entry_migration()`.
The `is_hugetlb_entry_migration()` helper function correctly handles this by first checking `huge_pte_none()`. Architectures like LoongArch can provide an override for `huge_pte_none()` that specifically recognizes the `invalid_pte_table` address as a "none" state for HugeTLB entries. This ensures `is_hugetlb_entry_migration()` returns false for the invalid entry, preventing the code from entering the faulty block.
This change makes the code reflect the likely original intent (handling migration) more accurately and leverages architecture-specific helpers (`huge_pte_none`) to correctly interpret special PTE/PMD values in the HugeTLB context, fixing the crash on LoongArch without altering the generic is_swap_pte() behavior.
Link: https://lkml.kernel.org/r/20250423010359.2030576-1-wangming01@loongson.cn Fixes: 25ee01a2fca0 ("mm: hugetlb: proc: add hugetlb-related fields to /proc/PID/smaps") Co-developed-by: Hongchen Zhang zhanghongchen@loongson.cn Signed-off-by: Hongchen Zhang zhanghongchen@loongson.cn Signed-off-by: Ming Wang wangming01@loongson.cn Cc: Andrii Nakryiko andrii@kernel.org Cc: Christophe Leroy christophe.leroy@csgroup.eu Cc: David Hildenbrand david@redhat.com Cc: David Rientjes rientjes@google.com Cc: Huacai Chen chenhuacai@kernel.org Cc: Hugh Dickins hughd@google.com Cc: Joern Engel joern@logfs.org Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: Michal Hocko mhocko@suse.cz Cc: Naoya Horiguchi nao.horiguchi@gmail.com Cc: Oscar Salvador osalvador@suse.de Cc: Ryan Roberts ryan.roberts@arm.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
fs/proc/task_mmu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/fs/proc/task_mmu.c~smaps-fix-crash-in-smaps_hugetlb_range-for-non-present-hugetlb-entries +++ a/fs/proc/task_mmu.c @@ -1027,7 +1027,7 @@ static int smaps_hugetlb_range(pte_t *pt if (pte_present(ptent)) { folio = page_folio(pte_page(ptent)); present = true; - } else if (is_swap_pte(ptent)) { + } else if (is_hugetlb_entry_migration(ptent)) { swp_entry_t swpent = pte_to_swp_entry(ptent);
if (is_pfn_swap_entry(swpent)) _
Patches currently in -mm which might be from wangming01@loongson.cn are
smaps-fix-crash-in-smaps_hugetlb_range-for-non-present-hugetlb-entries.patch