Re: [PATCH -next v2] uprobes: fix two zero old_folio bugs in __replace_page()

[Tong Tiangen <tongtiangen@huawei.com>]

在 2025/2/21 16:12, David Hildenbrand 写道:
> On 21.02.25 02:50, Tong Tiangen wrote:
>> We triggered the following error logs in syzkaller test:
>>
>>    BUG: Bad page state in process syz.7.38  pfn:1eff3
>>    page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 
>> pfn:0x1eff3
>>    flags: 
>> 0x3fffff00004004(referenced|reserved|node=0|zone=1|lastcpupid=0x1fffff)
>>    raw: 003fffff00004004 ffffe6c6c07bfcc8 ffffe6c6c07bfcc8 
>> 0000000000000000
>>    raw: 0000000000000000 0000000000000000 00000000fffffffe 
>> 0000000000000000
>>    page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set
>>    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 
>> 1.13.0-1ubuntu1.1 04/01/2014
>>    Call Trace:
>>     <TASK>
>>     dump_stack_lvl+0x32/0x50
>>     bad_page+0x69/0xf0
>>     free_unref_page_prepare+0x401/0x500
>>     free_unref_page+0x6d/0x1b0
>>     uprobe_write_opcode+0x460/0x8e0
>>     install_breakpoint.part.0+0x51/0x80
>>     register_for_each_vma+0x1d9/0x2b0
>>     __uprobe_register+0x245/0x300
>>     bpf_uprobe_multi_link_attach+0x29b/0x4f0
>>     link_create+0x1e2/0x280
>>     __sys_bpf+0x75f/0xac0
>>     __x64_sys_bpf+0x1a/0x30
>>     do_syscall_64+0x56/0x100
>>     entry_SYSCALL_64_after_hwframe+0x78/0xe2
>>
>>     BUG: Bad rss-counter state mm:00000000452453e0 type:MM_FILEPAGES 
>> val:-1
>>
>> The following syzkaller test case can be used to reproduce:
>>
>>    r2 = creat(&(0x7f0000000000)='./file0\x00', 0x8)
>>    write$nbd(r2, &(0x7f0000000580)=ANY=[], 0x10)
>>    r4 = openat(0xffffffffffffff9c, &(0x7f0000000040)='./file0\x00', 
>> 0x42, 0x0)
>>    mmap$IORING_OFF_SQ_RING(&(0x7f0000ffd000/0x3000)=nil, 0x3000, 0x0, 
>> 0x12, r4, 0x0)
>>    r5 = userfaultfd(0x80801)
>>    ioctl$UFFDIO_API(r5, 0xc018aa3f, &(0x7f0000000040)={0xaa, 0x20})
>>    r6 = userfaultfd(0x80801)
>>    ioctl$UFFDIO_API(r6, 0xc018aa3f, &(0x7f0000000140))
>>    ioctl$UFFDIO_REGISTER(r6, 0xc020aa00, 
>> &(0x7f0000000100)={{&(0x7f0000ffc000/0x4000)=nil, 0x4000}, 0x2})
>>    ioctl$UFFDIO_ZEROPAGE(r5, 0xc020aa04, 
>> &(0x7f0000000000)={{&(0x7f0000ffd000/0x1000)=nil, 0x1000}})
>>    r7 = bpf$PROG_LOAD(0x5, &(0x7f0000000140)={0x2, 0x3, 
>> &(0x7f0000000200)=ANY=[@ANYBLOB="1800000000120000000000000000000095"], 
>> &(0x7f0000000000)='GPL\x00', 0x7, 0x0, 0x0, 0x0, 0x0, '\x00', 0x0, 
>> @fallback=0x30, 0xffffffffffffffff, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 
>> 0x0, 0x0, 0x0, 0x0, 0x10, 0x0, @void, @value}, 0x94)
>>    bpf$BPF_LINK_CREATE_XDP(0x1c, &(0x7f0000000040)={r7, 0x0, 0x30, 
>> 0x1e, @val=@uprobe_multi={&(0x7f0000000080)='./file0\x00', 
>> &(0x7f0000000100)=[0x2], 0x0, 0x0, 0x1}}, 0x40)
>>
>> The cause is that zero pfn is set to the pte without increasing the rss
>> count in mfill_atomic_pte_zeropage() and the refcount of zero folio does
>> not increase accordingly. Then, the operation on the same pfn is 
>> performed
>> in uprobe_write_opcode()->__replace_page() to unconditional decrease the
>> rss count and old_folio's refcount.
>>
>> Therefore, two bugs are introduced:
>> 1. The rss count is incorrect, when process exit, the check_mm() report
>>     error "Bad rss-count".
>> 2. The reserved folio (zero folio) is freed when folio->refcount is zero,
>>     then free_pages_prepare->free_page_is_bad() report error
>>     "Bad page state".
> 
> Well, there is more, like triggering the
> 
>      VM_WARN_ON_FOLIO(is_zero_folio(folio), folio);
> 
> in __folio_rmap_sanity_checks() I assume.
> 
> So maybe just call the patch
> 
>      "uprobes: reject the share zeropage in uprobe_write_opcode)()"
> 
> Thanks!

OK, This subject is more appropriate.

Thanks.

>