Re: [PATCH stable 6.6] lib/buildid: Handle memfd_secret() files in build_id_parse()

[Sasha Levin <sashal@kernel.org>]

[ Sasha's backport helper bot ]

Hi,

Summary of potential issues:
⚠️ Found matching upstream commit but patch is missing proper reference to it

Found matching upstream commit: 5ac9b4e935dfc6af41eee2ddc21deb5c36507a9f

WARNING: Author mismatch between patch and found commit:
Backport author: Chen Linxuan<chenlinxuan@deepin.org>
Commit author: Andrii Nakryiko<andrii@kernel.org>

Status in newer kernel trees:
6.13.y | Present (exact SHA1)
6.12.y | Present (exact SHA1)

Note: The patch differs from the upstream commit:
---
1:  5ac9b4e935dfc ! 1:  9a5818b460ee4 lib/buildid: Handle memfd_secret() files in build_id_parse()
    @@
      ## Metadata ##
    -Author: Andrii Nakryiko <andrii@kernel.org>
    +Author: Chen Linxuan <chenlinxuan@deepin.org>
     
      ## Commit message ##
         lib/buildid: Handle memfd_secret() files in build_id_parse()
     
    -    >From memfd_secret(2) manpage:
    +    Backport of a similar change from commit 5ac9b4e935df ("lib/buildid:
    +    Handle memfd_secret() files in build_id_parse()") to address an issue
    +    where accessing secret memfd contents through build_id_parse() would
    +    trigger faults.
     
    -      The memory areas backing the file created with memfd_secret(2) are
    -      visible only to the processes that have access to the file descriptor.
    -      The memory region is removed from the kernel page tables and only the
    -      page tables of the processes holding the file descriptor map the
    -      corresponding physical memory. (Thus, the pages in the region can't be
    -      accessed by the kernel itself, so that, for example, pointers to the
    -      region can't be passed to system calls.)
    -
    -    We need to handle this special case gracefully in build ID fetching
    -    code. Return -EFAULT whenever secretmem file is passed to build_id_parse()
    -    family of APIs. Original report and repro can be found in [0].
    +    Original report and repro can be found in [0].
     
           [0] https://lore.kernel.org/bpf/ZwyG8Uro%2FSyTXAni@ly-workstation/
     
    -    Fixes: de3ec364c3c3 ("lib/buildid: add single folio-based file reader abstraction")
    -    Reported-by: Yi Lai <yi1.lai@intel.com>
    -    Suggested-by: Shakeel Butt <shakeel.butt@linux.dev>
    -    Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
    -    Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
    -    Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
    -    Link: https://lore.kernel.org/bpf/20241017175431.6183-A-hca@linux.ibm.com
    -    Link: https://lore.kernel.org/bpf/20241017174713.2157873-1-andrii@kernel.org
    +    This repro will cause BUG: unable to handle kernel paging request in
    +    build_id_parse in 5.15/6.1/6.6.
    +
    +    Some other discussions can be found in [1].
    +
    +      [1] https://lore.kernel.org/bpf/20241104175256.2327164-1-jolsa@kernel.org/T/#u
    +
    +    Cc: stable@vger.kernel.org
    +    Fixes: 88a16a130933 ("perf: Add build id data in mmap2 event")
    +    Signed-off-by: Chen Linxuan <chenlinxuan@deepin.org>
     
      ## lib/buildid.c ##
     @@
    @@ lib/buildid.c
      
      #define BUILD_ID 3
      
    -@@ lib/buildid.c: static int freader_get_folio(struct freader *r, loff_t file_off)
    - 
    - 	freader_put_folio(r);
    +@@ lib/buildid.c: int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,
    + 	if (!vma->vm_file)
    + 		return -EINVAL;
      
    ++#ifdef CONFIG_SECRETMEM
     +	/* reject secretmem folios created with memfd_secret() */
    -+	if (secretmem_mapping(r->file->f_mapping))
    ++	if (vma->vm_file->f_mapping->a_ops == &secretmem_aops)
     +		return -EFAULT;
    ++#endif
     +
    - 	r->folio = filemap_get_folio(r->file->f_mapping, file_off >> PAGE_SHIFT);
    - 
    - 	/* if sleeping is allowed, wait for the page, if necessary */
    + 	page = find_get_page(vma->vm_file->f_mapping, 0);
    + 	if (!page)
    + 		return -EFAULT;	/* page not mapped */
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-6.6.y        |  Success    |  Success   |