Jeff Xu <jef...@chromium.org> wrote: > On Thu, Feb 1, 2024 at 3:11 PM Eric Biggers <ebigg...@kernel.org> wrote: > > > > On Wed, Jan 31, 2024 at 05:50:24PM +0000, jef...@chromium.org wrote: > > > [PATCH v8 2/4] mseal: add mseal syscall > > [...] > > > +/* > > > + * The PROT_SEAL defines memory sealing in the prot argument of mmap(). > > > + */ > > > +#define PROT_SEAL 0x04000000 /* _BITUL(26) */ > > > + > > > /* 0x01 - 0x03 are defined in linux/mman.h */ > > > #define MAP_TYPE 0x0f /* Mask for type of mapping */ > > > #define MAP_FIXED 0x10 /* Interpret addr exactly */ > > > @@ -33,6 +38,9 @@ > > > #define MAP_UNINITIALIZED 0x4000000 /* For anonymous mmap, memory could > > > be > > > * uninitialized */ > > > > > > +/* map is sealable */ > > > +#define MAP_SEALABLE 0x8000000 /* _BITUL(27) */ > > > > IMO this patch is misleading, as it claims to just be adding a new syscall, > > but > > it actually adds three new UAPIs, only one of which is the new syscall. The > > other two new UAPIs are new flags to the mmap syscall. > > > The description does include all three. I could update the patch title. > > > Based on recent discussions, it seems the usefulness of the new mmap flags > > has > > not yet been established. Note also that there are only a limited number of > > mmap flags remaining, so we should be careful about allocating them. > > > > Therefore, why not start by just adding the mseal syscall, without the new > > mmap > > flags alongside it? > > > > I'll also note that the existing PROT_* flags seem to be conventionally > > used for > > the CPU page protections, as opposed to kernel-specific properties of the > > VMA > > object. As such, PROT_SEAL feels a bit out of place anyway. If it's added > > at > > all it perhaps should be a MAP_* flag, not PROT_*. I'm not sure this > > aspect has > > been properly discussed yet, seeing as the patchset is presented as just > > adding > > sys_mseal(). Some reviewers may not have noticed or considered the new > > flags. > > > MAP_ flags is more used for type of mapping, such as MAP_FIXED_NOREPLACE. > > The PROT_SEAL might make more sense because sealing the protection bit > is the main functionality of the sealing at this moment.
Jeff, please show a piece of software that needs to do PROT_SEAL as mprotect() or mmap() argument. Please don't write it as a vague essay. Instead, take a piece of existing code, write a diff, and show your work. Then explain that diff, justify why doing the PROT_SEAL as an argument of mprotect() or mmap() is a required improvement, and show your Linux developer peers that you can do computer science. I did the same work in OpenBSD, at least 25% time over 2 years, and I had to prove my work inside my development community. I had to prove that it worked system wide, not in 1 program, with hand-waving for the rest. If I had said "Looks, it works in ssh, trust me it works in other programs", it would not have gone further. glibc is the best example to demonstrate, but smaller examples might convince.
