On Tue, Jan 16, 2024 at 09:09:45AM +0100, Ard Biesheuvel wrote: > (cc Kees, LAKML) > > https://lkml.kernel.org/r/69fa6015256613ed10aee996e181ebd4%40horotw.com > > On Mon, 15 Jan 2024 at 21:46, Matthew Wilcox <[email protected]> wrote: > > > ... > > Yeah, I don't know either. Outside my scope of expertise. > > > > I received a suggestion off-list that we only do the PMD alignment on > > 64-bit, which seems quite reasonable to me. After all, I don't care > > about performance on 32-bit just as much as I don't care about security > > on 32-bit. > > > > For context, the culprit is > > commit 1854bc6e2420472676c5c90d3d6b15f6cd640e40 > Author: William Kucharski <[email protected]> > Date: Sun Sep 22 08:43:15 2019 -0400 > > mm/readahead: Align file mappings for non-DAX > > When we have the opportunity to use PMDs to map a file, we want to follow > the same rules as DAX. > > Signed-off-by: William Kucharski <[email protected]> > Signed-off-by: Matthew Wilcox (Oracle) <[email protected]> > > which affects *all* 32-bit architectures not just i686. 32-bit ARM > user space is still being deployed widely, even on arm64 Chromebooks > running 64-bit kernels (at least up until recently) so unfortunately, > we're not quite at the point yet where we can just let it rot.
Is this related at all to this thread as well? https://lore.kernel.org/lkml/[email protected]/ Can we avoid this on 32-bit or at least not mislead userspace about the available entropy visible in /proc/sys/vm/mmap_rnd*_bits ? -Kees -- Kees Cook
