Messages in this thread | | | Subject | Re: [PATCH 1/1 v2] x86: pkey-mprotect must allow pkey-0 | From | Dave Hansen <> | Date | Wed, 14 Mar 2018 07:19:23 -0700 |
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On 03/14/2018 12:46 AM, Ram Pai wrote: > Once an address range is associated with an allocated pkey, it cannot be > reverted back to key-0. There is no valid reason for the above behavior. On > the contrary applications need the ability to do so.
I'm trying to remember why we cared in the first place. :)
Could you add that to the changelog, please?
> @@ -92,7 +92,8 @@ int mm_pkey_alloc(struct mm_struct *mm) > static inline > int mm_pkey_free(struct mm_struct *mm, int pkey) > { > - if (!mm_pkey_is_allocated(mm, pkey)) > + /* pkey 0 is special and can never be freed */ > + if (!pkey || !mm_pkey_is_allocated(mm, pkey)) > return -EINVAL;
If an app was being really careful, couldn't it free up all of the implicitly-pkey-0-assigned memory so that it is not in use at all? In that case, we might want to allow this.
On the other hand, nobody is likely to _ever_ actually do this so this is good shoot-yourself-in-the-foot protection.
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