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SubjectRe: [PATCH] mm/mprotect: Only reference swap pfn page if type match
On 24.08.22 00:11, Peter Xu wrote:
> Yu Zhao reported a bug after the commit "mm/swap: Add swp_offset_pfn() to
> fetch PFN from swap entry" added a check in swp_offset_pfn() for swap type [1]:
>
> kernel BUG at include/linux/swapops.h:117!
> CPU: 46 PID: 5245 Comm: EventManager_De Tainted: G S O L 6.0.0-dbg-DEV #2
> RIP: 0010:pfn_swap_entry_to_page+0x72/0xf0
> Code: c6 48 8b 36 48 83 fe ff 74 53 48 01 d1 48 83 c1 08 48 8b 09 f6
> c1 01 75 7b 66 90 48 89 c1 48 8b 09 f6 c1 01 74 74 5d c3 eb 9e <0f> 0b
> 48 ba ff ff ff ff 03 00 00 00 eb ae a9 ff 0f 00 00 75 13 48
> RSP: 0018:ffffa59e73fabb80 EFLAGS: 00010282
> RAX: 00000000ffffffe8 RBX: 0c00000000000000 RCX: ffffcd5440000000
> RDX: 1ffffffffff7a80a RSI: 0000000000000000 RDI: 0c0000000000042b
> RBP: ffffa59e73fabb80 R08: ffff9965ca6e8bb8 R09: 0000000000000000
> R10: ffffffffa5a2f62d R11: 0000030b372e9fff R12: ffff997b79db5738
> R13: 000000000000042b R14: 0c0000000000042b R15: 1ffffffffff7a80a
> FS: 00007f549d1bb700(0000) GS:ffff99d3cf680000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000440d035b3180 CR3: 0000002243176004 CR4: 00000000003706e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> <TASK>
> change_pte_range+0x36e/0x880
> change_p4d_range+0x2e8/0x670
> change_protection_range+0x14e/0x2c0
> mprotect_fixup+0x1ee/0x330
> do_mprotect_pkey+0x34c/0x440
> __x64_sys_mprotect+0x1d/0x30
>
> It triggers because pfn_swap_entry_to_page() could be called upon e.g. a
> genuine swap entry.
>
> Fix it by only calling it when it's a write migration entry where the page*
> is used.
>
> [1] https://lore.kernel.org/lkml/CAOUHufaVC2Za-p8m0aiHw6YkheDcrO-C3wRGixwDS32VTS+k1w@mail.gmail.com/
>
> Fixes: 6c287605fd56 ("mm: remember exclusively mapped anonymous pages with PG_anon_exclusive")
> Cc: David Hildenbrand <david@redhat.com>
> Cc: <stable@vger.kernel.org>
> Reported-by: Yu Zhao <yuzhao@google.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
> mm/mprotect.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index f2b9b1da9083..4549f5945ebe 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -203,10 +203,11 @@ static unsigned long change_pte_range(struct mmu_gather *tlb,
> pages++;
> } else if (is_swap_pte(oldpte)) {
> swp_entry_t entry = pte_to_swp_entry(oldpte);
> - struct page *page = pfn_swap_entry_to_page(entry);
> pte_t newpte;
>
> if (is_writable_migration_entry(entry)) {
> + struct page *page = pfn_swap_entry_to_page(entry);
> +
> /*
> * A protection check is difficult so
> * just be safe and disable write


Stumbling over the THP code, I was wondering if we also want to adjust change_huge_pmd()
and hugetlb_change_protection. There are no actual swap entries, so I assume we're fine.


diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 482c1826e723..466364e7fc5f 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1798,10 +1798,10 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
if (is_swap_pmd(*pmd)) {
swp_entry_t entry = pmd_to_swp_entry(*pmd);
- struct page *page = pfn_swap_entry_to_page(entry);

VM_BUG_ON(!is_pmd_migration_entry(*pmd));
if (is_writable_migration_entry(entry)) {
+ struct page *page = pfn_swap_entry_to_page(entry);
pmd_t newpmd;
/*
* A protection check is difficult so
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 2480ba627aa5..559465fae5cd 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6370,9 +6370,9 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
}
if (unlikely(is_hugetlb_entry_migration(pte))) {
swp_entry_t entry = pte_to_swp_entry(pte);
- struct page *page = pfn_swap_entry_to_page(entry);

if (!is_readable_migration_entry(entry)) {
+ struct page *page = pfn_swap_entry_to_page(entry);
pte_t newpte;

if (PageAnon(page))

@Peter, what's your thought?

--
Thanks,

David / dhildenb

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