Add Morton,Peter and David for discussion//Re: [PATCH -next] uprobes: fix two zero old_folio bugs in __replace_page()

Add Morton,Peter and David for discussion//Re: [PATCH -next] uprobes: fix two zero old_folio bugs in __replace_page()

[Tong Tiangen]

在 2025/2/17 20:38, Tong Tiangen 写道:
> 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".
> 
> To fix it, add zero folio check before rss counter and refcount decrease.
> 
> Fixes: 7396fa818d62 ("uprobes/core: Make background page replacement logic account for rss_stat counters")
> Fixes: 2b1444983508 ("uprobes, mm, x86: Add the ability to install and remove uprobes breakpoints")
> Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>
> ---
>   kernel/events/uprobes.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 46ddf3a2334d..ff5694acfa68 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -213,7 +213,8 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
>   		dec_mm_counter(mm, MM_ANONPAGES);
>   
>   	if (!folio_test_anon(old_folio)) {
> -		dec_mm_counter(mm, mm_counter_file(old_folio));
> +		if (!is_zero_folio(old_folio))
> +			dec_mm_counter(mm, mm_counter_file(old_folio));
>   		inc_mm_counter(mm, MM_ANONPAGES);
>   	}
>   
> @@ -227,7 +228,8 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
>   	if (!folio_mapped(old_folio))
>   		folio_free_swap(old_folio);
>   	page_vma_mapped_walk_done(&pvmw);
> -	folio_put(old_folio);
> +	if (!is_zero_folio(old_folio))
> +		folio_put(old_folio);
>   
>   	err = 0;
>    unlock:

Re: Add Morton,Peter and David for discussion//Re: [PATCH -next] uprobes: fix two zero old_folio bugs in __replace_page()

[David Hildenbrand]

On 18.02.25 03:47, Tong Tiangen wrote:
> 
> 
> 在 2025/2/17 20:38, Tong Tiangen 写道:
>> 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".
>>
>> To fix it, add zero folio check before rss counter and refcount decrease.
>>
>> Fixes: 7396fa818d62 ("uprobes/core: Make background page replacement logic account for rss_stat counters")
>> Fixes: 2b1444983508 ("uprobes, mm, x86: Add the ability to install and remove uprobes breakpoints")
>> Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>
>> ---
>>    kernel/events/uprobes.c | 6 ++++--
>>    1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
>> index 46ddf3a2334d..ff5694acfa68 100644
>> --- a/kernel/events/uprobes.c
>> +++ b/kernel/events/uprobes.c
>> @@ -213,7 +213,8 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
>>    		dec_mm_counter(mm, MM_ANONPAGES);
>>    
>>    	if (!folio_test_anon(old_folio)) {
>> -		dec_mm_counter(mm, mm_counter_file(old_folio));
>> +		if (!is_zero_folio(old_folio))
>> +			dec_mm_counter(mm, mm_counter_file(old_folio));
>>    		inc_mm_counter(mm, MM_ANONPAGES);
>>    	}
>>    
>> @@ -227,7 +228,8 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
>>    	if (!folio_mapped(old_folio))
>>    		folio_free_swap(old_folio);
>>    	page_vma_mapped_walk_done(&pvmw);
>> -	folio_put(old_folio);
>> +	if (!is_zero_folio(old_folio))
>> +		folio_put(old_folio);
 >>    >>    	err = 0;
>>     unlock:
> 

The whole "manually replace pages" logic is fragile. I tried to rewrite 
it a while back:

https://lkml.kernel.org/r/20240604122548.359952-1-david@redhat.com

But didn't get to follow-up yet.

I'm not sure if the page_vma_mapped_walk() really does what we would 
expect here.

The folio_remove_rmap_pte(old_folio, old_page, vma); is certainly wrong 
as well for ero folios.


I don't think there is a sane use case right now where we would hit the 
shared zeropage.

So for the time being, I think we should just reject them immediately 
after get_user_page_vma_remote().

At some point I'll follow up with my rewrite that will clean this 
nastiness here up a bit.

-- 
Cheers,

David / dhildenb

Re: Add Morton,Peter and David for discussion//Re: [PATCH -next] uprobes: fix two zero old_folio bugs in __replace_page()

[Tong Tiangen]

在 2025/2/18 16:23, David Hildenbrand 写道:
> On 18.02.25 03:47, Tong Tiangen wrote:
>>
>>
>> 在 2025/2/17 20:38, Tong Tiangen 写道:
>>> 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".
>>>
>>> To fix it, add zero folio check before rss counter and refcount 
>>> decrease.
>>>
>>> Fixes: 7396fa818d62 ("uprobes/core: Make background page replacement 
>>> logic account for rss_stat counters")
>>> Fixes: 2b1444983508 ("uprobes, mm, x86: Add the ability to install 
>>> and remove uprobes breakpoints")
>>> Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>
>>> ---
>>>    kernel/events/uprobes.c | 6 ++++--
>>>    1 file changed, 4 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
>>> index 46ddf3a2334d..ff5694acfa68 100644
>>> --- a/kernel/events/uprobes.c
>>> +++ b/kernel/events/uprobes.c
>>> @@ -213,7 +213,8 @@ static int __replace_page(struct vm_area_struct 
>>> *vma, unsigned long addr,
>>>            dec_mm_counter(mm, MM_ANONPAGES);
>>>        if (!folio_test_anon(old_folio)) {
>>> -        dec_mm_counter(mm, mm_counter_file(old_folio));
>>> +        if (!is_zero_folio(old_folio))
>>> +            dec_mm_counter(mm, mm_counter_file(old_folio));
>>>            inc_mm_counter(mm, MM_ANONPAGES);
>>>        }
>>> @@ -227,7 +228,8 @@ static int __replace_page(struct vm_area_struct 
>>> *vma, unsigned long addr,
>>>        if (!folio_mapped(old_folio))
>>>            folio_free_swap(old_folio);
>>>        page_vma_mapped_walk_done(&pvmw);
>>> -    folio_put(old_folio);
>>> +    if (!is_zero_folio(old_folio))
>>> +        folio_put(old_folio);
>  >>    >>        err = 0;
>>>     unlock:
>>
> 
> The whole "manually replace pages" logic is fragile. I tried to rewrite 
> it a while back:
> 
> https://lkml.kernel.org/r/20240604122548.359952-1-david@redhat.com
> 
> But didn't get to follow-up yet.
> 
> I'm not sure if the page_vma_mapped_walk() really does what we would 
> expect here.
> 
> The folio_remove_rmap_pte(old_folio, old_page, vma); is certainly wrong 
> as well for ero folios.
> 
> 
> I don't think there is a sane use case right now where we would hit the 
> shared zeropage.
> 
> So for the time being, I think we should just reject them immediately 
> after get_user_page_vma_remote().
> 
> At some point I'll follow up with my rewrite that will clean this 
> nastiness here up a bit.

OK, Before your rewrite last merged, How about i change the solution to
just reject them immediately after get_user_page_vma_remote()？

Thanks,
Tong.

> 

Re: Add Morton,Peter and David for discussion//Re: [PATCH -next] uprobes: fix two zero old_folio bugs in __replace_page()

[Oleg Nesterov]

On 02/18, Tong Tiangen wrote:
>
> OK, Before your rewrite last merged, How about i change the solution to
> just reject them immediately after get_user_page_vma_remote()？

I agree, uprobe_write_opcode() should simply fail if is_zero_page(old_page).

Oleg.

Re: Add Morton,Peter and David for discussion//Re: [PATCH -next] uprobes: fix two zero old_folio bugs in __replace_page()

[David Hildenbrand]

On 19.02.25 16:22, Oleg Nesterov wrote:
> On 02/18, Tong Tiangen wrote:
>>
>> OK, Before your rewrite last merged, How about i change the solution to
>> just reject them immediately after get_user_page_vma_remote()？
> 
> I agree, uprobe_write_opcode() should simply fail if is_zero_page(old_page).

Yes. That's currently only syzkaller that triggers it, not some sane use 
case.

-- 
Cheers,

David / dhildenb

Re: Add Morton,Peter and David for discussion//Re: [PATCH -next] uprobes: fix two zero old_folio bugs in __replace_page()

[Tong Tiangen]

在 2025/2/20 0:12, David Hildenbrand 写道:
> On 19.02.25 16:22, Oleg Nesterov wrote:
>> On 02/18, Tong Tiangen wrote:
>>>
>>> OK, Before your rewrite last merged, How about i change the solution to
>>> just reject them immediately after get_user_page_vma_remote()？
>>
>> I agree, uprobe_write_opcode() should simply fail if 
>> is_zero_page(old_page).
> 
> Yes. That's currently only syzkaller that triggers it, not some sane use 
> case.

OK, change as follows:

--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -506,6 +506,12 @@ int uprobe_write_opcode(struct arch_uprobe 
*auprobe, struct mm_struct *mm,
         if (ret <= 0)
                 goto put_old;

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

If ok, i will send v2 soon.

Thanks,
Tong.

> 

Re: Add Morton,Peter and David for discussion//Re: [PATCH -next] uprobes: fix two zero old_folio bugs in __replace_page()

[David Hildenbrand]

On 20.02.25 03:31, Tong Tiangen wrote:
> 
> 
> 在 2025/2/20 0:12, David Hildenbrand 写道:
>> On 19.02.25 16:22, Oleg Nesterov wrote:
>>> On 02/18, Tong Tiangen wrote:
>>>>
>>>> OK, Before your rewrite last merged, How about i change the solution to
>>>> just reject them immediately after get_user_page_vma_remote()？
>>>
>>> I agree, uprobe_write_opcode() should simply fail if
>>> is_zero_page(old_page).
>>
>> Yes. That's currently only syzkaller that triggers it, not some sane use
>> case.
> 
> OK, change as follows:
> 
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -506,6 +506,12 @@ int uprobe_write_opcode(struct arch_uprobe
> *auprobe, struct mm_struct *mm,
>           if (ret <= 0)
>                   goto put_old;
> 
> +       if (WARN(is_zero_page(old_page),

This can likely be triggered by user space, so do not use WARN.

-- 
Cheers,

David / dhildenb

Re: Add Morton,Peter and David for discussion//Re: [PATCH -next] uprobes: fix two zero old_folio bugs in __replace_page()

[Tong Tiangen]

在 2025/2/20 16:38, David Hildenbrand 写道:
> On 20.02.25 03:31, Tong Tiangen wrote:
>>
>>
>> 在 2025/2/20 0:12, David Hildenbrand 写道:
>>> On 19.02.25 16:22, Oleg Nesterov wrote:
>>>> On 02/18, Tong Tiangen wrote:
>>>>>
>>>>> OK, Before your rewrite last merged, How about i change the 
>>>>> solution to
>>>>> just reject them immediately after get_user_page_vma_remote()？
>>>>
>>>> I agree, uprobe_write_opcode() should simply fail if
>>>> is_zero_page(old_page).
>>>
>>> Yes. That's currently only syzkaller that triggers it, not some sane use
>>> case.
>>
>> OK, change as follows:
>>
>> --- a/kernel/events/uprobes.c
>> +++ b/kernel/events/uprobes.c
>> @@ -506,6 +506,12 @@ int uprobe_write_opcode(struct arch_uprobe
>> *auprobe, struct mm_struct *mm,
>>           if (ret <= 0)
>>                   goto put_old;
>>
>> +       if (WARN(is_zero_page(old_page),
> 
> This can likely be triggered by user space, so do not use WARN.

OK,thanks.

Hi Oleg, is that all right?

Thanks,
Tong.

> 

Re: Add Morton,Peter and David for discussion//Re: [PATCH -next] uprobes: fix two zero old_folio bugs in __replace_page()

[Oleg Nesterov]

On 02/20, Tong Tiangen wrote:
>
> 在 2025/2/20 16:38, David Hildenbrand 写道:
> >On 20.02.25 03:31, Tong Tiangen wrote:
> >>
> >>@@ -506,6 +506,12 @@ int uprobe_write_opcode(struct arch_uprobe
> >>*auprobe, struct mm_struct *mm,
> >>          if (ret <= 0)
> >>                  goto put_old;
> >>
> >>+       if (WARN(is_zero_page(old_page),
> >
> >This can likely be triggered by user space, so do not use WARN.
>
> OK,thanks.
>
> Hi Oleg, is that all right?

Thanks, LGTM.

Oleg.

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

[Tong Tiangen]

在 2025/2/18 0:12, Oleg Nesterov 写道:
> Can't comment, my understanding of mm/ is not enough these days.
> 
> Just one question...
> 
> On 02/17, Tong Tiangen wrote:
>>
>> Fixes: 7396fa818d62 ("uprobes/core: Make background page replacement logic account for rss_stat counters")
>> Fixes: 2b1444983508 ("uprobes, mm, x86: Add the ability to install and remove uprobes breakpoints")
> 
> Are you sure this logic was wrong from the very beginning? Just curious.
> 
> Oleg.

Yes, i checked the original code logic, and the put_page() didn't take 
zero pages into account.

Add Morton,Peter and David for discussion.

Thanks,
Tong.

> 
>> Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>
>> ---
>>   kernel/events/uprobes.c | 6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
>> index 46ddf3a2334d..ff5694acfa68 100644
>> --- a/kernel/events/uprobes.c
>> +++ b/kernel/events/uprobes.c
>> @@ -213,7 +213,8 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
>>   		dec_mm_counter(mm, MM_ANONPAGES);
>>   
>>   	if (!folio_test_anon(old_folio)) {
>> -		dec_mm_counter(mm, mm_counter_file(old_folio));
>> +		if (!is_zero_folio(old_folio))
>> +			dec_mm_counter(mm, mm_counter_file(old_folio));
>>   		inc_mm_counter(mm, MM_ANONPAGES);
>>   	}
>>   
>> @@ -227,7 +228,8 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
>>   	if (!folio_mapped(old_folio))
>>   		folio_free_swap(old_folio);
>>   	page_vma_mapped_walk_done(&pvmw);
>> -	folio_put(old_folio);
>> +	if (!is_zero_folio(old_folio))
>> +		folio_put(old_folio);
>>   
>>   	err = 0;
>>    unlock:
>> -- 
>> 2.25.1
>>
> 
> 
> .