On Mon, 2015-09-28 at 12:18 -0700, Dave Hansen wrote: > From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> > > mprotect_key() is just like mprotect, except it also takes a > protection key as an argument. On systems that do not support > protection keys, it still works, but requires that key=0. I'm not sure how userspace is going to use the key=0 feature? ie. userspace will still have to detect that keys are not supported and use key 0 everywhere. At that point it could just as well skip the mprotect_key() syscalls entirely couldn't it? > I expect it to get used like this, if you want to guarantee that > any mapping you create can *never* be accessed without the right > protection keys set up. > > pkey_deny_access(11); // random pkey > int real_prot = PROT_READ|PROT_WRITE; > ptr = mmap(NULL, PAGE_SIZE, PROT_NONE, MAP_ANONYMOUS|MAP_PRIVATE, -1, 0); > ret = mprotect_key(ptr, PAGE_SIZE, real_prot, 11); > > This way, there is *no* window where the mapping is accessible > since it was always either PROT_NONE or had a protection key set. > > We settled on 'unsigned long' for the type of the key here. We > only need 4 bits on x86 today, but I figured that other > architectures might need some more space. If the existing mprotect() syscall had a flags argument you could have just used that. So is it worth just adding mprotect2() now and using it for this? ie: int mprotect2(unsigned long start, size_t len, unsigned long prot, unsigned long flags) .. And then you define bit zero of flags to say you're passing a pkey, and it's in bits 1-63? That way if other arches need to do something different you at least have the flags available? cheers -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>