Re: [PATCH] mm/mprotect: Only reference swap pfn page if type match

[Yu Zhao]

On Tue, Aug 23, 2022 at 4:11 PM Peter Xu <peterx@xxxxxxxxxx> 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@xxxxxxxxxxxxxx/
>
> Fixes: 6c287605fd56 ("mm: remember exclusively mapped anonymous pages with PG_anon_exclusive")
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Reported-by: Yu Zhao <yuzhao@xxxxxxxxxx>
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>

Thanks for the quick turnaround!

Tested-by: Yu Zhao <yuzhao@xxxxxxxxxx>