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

[Chen Linxuan]

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.

Original report and repro can be found in [0].

  [0] https://lore.kernel.org/bpf/ZwyG8Uro%2FSyTXAni@ly-workstation/

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@xxxxxxxxxx/T/#u

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 88a16a130933 ("perf: Add build id data in mmap2 event")
Signed-off-by: Chen Linxuan <chenlinxuan@xxxxxxxxxx>
---
 lib/buildid.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/lib/buildid.c b/lib/buildid.c
index 9fc46366597e..b78d119ed1f7 100644
--- a/lib/buildid.c
+++ b/lib/buildid.c
@@ -157,6 +157,12 @@ 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 (vma->vm_file->f_mapping->a_ops == &secretmem_aops)
+		return -EFAULT;
+#endif
+
 	page = find_get_page(vma->vm_file->f_mapping, 0);
 	if (!page)
 		return -EFAULT;	/* page not mapped */
-- 
2.48.1