On Wed, Jul 12, 2017 at 07:29:37AM +1000, Benjamin Herrenschmidt wrote: > On Tue, 2017-07-11 at 11:11 -0700, Dave Hansen wrote: > > On 07/05/2017 02:21 PM, Ram Pai wrote: > > > Currently sys_pkey_create() provides the ability to disable read > > > and write permission on the key, at creation. powerpc has the > > > hardware support to disable execute on a pkey as well.This patch > > > enhances the interface to let disable execute at key creation > > > time. x86 does not allow this. Hence the next patch will add > > > ability in x86 to return error if PKEY_DISABLE_EXECUTE is > > > specified. > > That leads to the question... How do you tell userspace. > > (apologies if I missed that in an existing patch in the series) > > How do we inform userspace of the key capabilities ? There are at least > two things userspace may want to know already: > > - What protection bits are supported for a key the userspace is the one which allocates the keys and enables/disables the protection bits on the key. the kernel is just a facilitator. Now if the use space wants to know the current permissions on a given key, it can just read the AMR/PKRU register on powerpc/intel respectively. > > - How many keys exist There is no standard way of finding this other than trying to allocate as many till you fail. A procfs or sysfs file can be added to expose this information. > > - Which keys are available for use by userspace. On PowerPC, the > kernel can reserve some keys for itself, so can the hypervisor. In > fact, they do. this information can be exposed through /proc or /sysfs I am sure there will be more demands and requirements as applications start leveraging these feature. RP > > Cheers, > Ben. -- Ram Pai -- 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>
