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...
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