Re: [PATCH 1/1 v2] x86: pkey-mprotect must allow pkey-0
flat view
From: Dave Hansen <hidden>
Date: 2018-03-14 14:19:28
Also in:
linux-arch, linux-mm, lkml
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?
quoted hunk ↗ jump to hunk
@@ -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.