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

[Tong Tiangen <tongtiangen@huawei.com>]

在 2025/2/22 10:37, Tong Tiangen 写道:
> 
> 
> 在 2025/2/21 23:28, Oleg Nesterov 写道:
>> On 02/21, Tong Tiangen wrote:
>>>
>>> --- a/kernel/events/uprobes.c
>>> +++ b/kernel/events/uprobes.c
>>> @@ -506,6 +506,11 @@ int uprobe_write_opcode(struct arch_uprobe 
>>> *auprobe, struct mm_struct *mm,
>>>       if (ret <= 0)
>>>           goto put_old;
>>>
>>> +    if (is_zero_page(old_page)) {
>>> +        ret = -EINVAL;
>>> +        goto put_old;
>>> +    }
>>
>> I agree with David, the subject looks a bit misleading.
>>
>> And. I won't insist, this is cosmetic, but if you send V2 please consider
>> moving the "verify_opcode()" check down, after the 
>> is_zero_page/PageCompound
>> checks.
>>
>> Oleg.
> 
> OK, check the validity of the old page first and modify the subject in
> v3 .
> 
> Thanks.

I'm going to add a new patch to moving the "verify_opcode()" check down
, IIUC that "!PageAnon(old_page)" below also needs to be moved together,
and as David said this can be triggered by user space, so delete the use
  of "WARN", as follows:


@@ -502,20 +502,16 @@ int uprobe_write_opcode(struct arch_uprobe 
*auprobe, struct mm_struct *mm,
         if (IS_ERR(old_page))
                 return PTR_ERR(old_page);

-       ret = verify_opcode(old_page, vaddr, &opcode);
-       if (ret <= 0)
+       ret = -EINVAL;
+       if (is_zero_page(old_page))
                 goto put_old;

-       if (is_zero_page(old_page)) {
-               ret = -EINVAL;
+       if (!is_register && (PageCompound(old_page) || !PageAnon(old_page)))
                 goto put_old;
-       }

-       if (WARN(!is_register && PageCompound(old_page),
-                "uprobe unregister should never work on compound 
page\n")) {
-               ret = -EINVAL;
+       ret = verify_opcode(old_page, vaddr, &opcode);
+       if (ret <= 0)
                 goto put_old;
-       }

         /* We are going to replace instruction, update ref_ctr. */
         if (!ref_ctr_updated && uprobe->ref_ctr_offset) {
@@ -526,10 +522,6 @@ int uprobe_write_opcode(struct arch_uprobe 
*auprobe, struct mm_struct *mm,
                 ref_ctr_updated = 1;
         }

-       ret = 0;
-       if (!is_register && !PageAnon(old_page))
-               goto put_old;
-
         ret = anon_vma_prepare(vma);

Thanks.
> 
>>
>>
>> .
> 
> .