Ccing couple more folks who are doing similar work (ASI, guest_memfd) Folks, what is the generic way to check if a given mapping has folios unmapped from kernel address space? On Mon, Oct 14, 2024 at 04:56:31PM GMT, Andrii Nakryiko wrote: > From memfd_secret(2) manpage: > > 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 -EACCESS whenever secretmem file is passed to build_id_parse() > family of APIs. Original report and repro can be found in [0]. > > [0] https://lore.kernel.org/bpf/ZwyG8Uro%2FSyTXAni@ly-workstation/ > > Reported-by: Yi Lai <yi1.lai@xxxxxxxxx> > Suggested-by: Shakeel Butt <shakeel.butt@xxxxxxxxx> > Fixes: de3ec364c3c3 ("lib/buildid: add single folio-based file reader abstraction") > Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx> > --- > lib/buildid.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/lib/buildid.c b/lib/buildid.c > index 290641d92ac1..f0e6facf61c5 100644 > --- a/lib/buildid.c > +++ b/lib/buildid.c > @@ -5,6 +5,7 @@ > #include <linux/elf.h> > #include <linux/kernel.h> > #include <linux/pagemap.h> > +#include <linux/secretmem.h> > > #define BUILD_ID 3 > > @@ -64,6 +65,10 @@ static int freader_get_folio(struct freader *r, loff_t file_off) > > freader_put_folio(r); > > + /* reject secretmem folios created with memfd_secret() */ > + if (secretmem_mapping(r->file->f_mapping)) > + return -EACCES; > + > r->folio = filemap_get_folio(r->file->f_mapping, file_off >> PAGE_SHIFT); > > /* if sleeping is allowed, wait for the page, if necessary */ > -- > 2.43.5 >
