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. 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. - Eric
