On Wed, Oct 30, 2019 at 09:19:33AM +0100, David Hildenbrand wrote: > On 30.10.19 09:15, Mike Rapoport wrote: > >On Tue, Oct 29, 2019 at 12:02:34PM +0100, David Hildenbrand wrote: > >>On 27.10.19 11:17, Mike Rapoport wrote: > >>>From: Mike Rapoport <rppt@xxxxxxxxxxxxx> > >>> > >>>The mappings created with MAP_EXCLUSIVE are visible only in the context of > >>>the owning process and can be used by applications to store secret > >>>information that will not be visible not only to other processes but to the > >>>kernel as well. > >>> > >>>The pages in these mappings are removed from the kernel direct map and > >>>marked with PG_user_exclusive flag. When the exclusive area is unmapped, > >>>the pages are mapped back into the direct map. > >>> > >> > >>Just a thought, the kernel is still able to indirectly read the contents of > >>these pages by doing a kdump from kexec environment, right? > > > >Right. > > > >>Also, I wonder > >>what would happen if you map such pages via /dev/mem into another user space > >>application and e.g., use them along with kvm [1]. > > > >Do you mean that one application creates MAP_EXCLUSIVE and another > >applications accesses the same physical pages via /dev/mem? > > Exactly. > > > > >With /dev/mem all physical memory is visible... > > Okay, so the statement "information that will not be visible not only to > other processes but to the kernel as well" is not correct. There are easy > ways to access that information if you really want to (might require root > permissions, though). Right, but /dev/mem is an easy way to extract any information in any environment if one has root permissions... > -- > > Thanks, > > David / dhildenb > -- Sincerely yours, Mike.
