Re: [PATCH] x86, powerpc : pkey-mprotect must allow pkey-0
From: Michael Ellerman <mpe@ellerman.id.au>
Date: 2018-03-09 10:20:01
Also in:
linux-arch, linux-mm, lkml
Ram Pai [off-list ref] writes:
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.
Please explain this in much more detail. Is it an ABI change? And why did we just notice this?
The patch relaxes the restriction. Tested on powerpc and x86_64.
Thanks, but please split the patch, one for each arch. cheers
quoted hunk ↗ jump to hunk
diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h index 0409c80..3e8abe4 100644 --- a/arch/powerpc/include/asm/pkeys.h +++ b/arch/powerpc/include/asm/pkeys.h@@ -101,10 +101,18 @@ static inline u16 pte_to_pkey_bits(u64 pteflags) static inline bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey) { - /* A reserved key is never considered as 'explicitly allocated' */ - return ((pkey < arch_max_pkey()) && - !__mm_pkey_is_reserved(pkey) && - __mm_pkey_is_allocated(mm, pkey)); + /* pkey 0 is allocated by default. */ + if (!pkey) + return true; + + if (pkey < 0 || pkey >= arch_max_pkey()) + return false; + + /* reserved keys are never allocated. */ + if (__mm_pkey_is_reserved(pkey)) + return false; + + return(__mm_pkey_is_allocated(mm, pkey)); } extern void __arch_activate_pkey(int pkey);@@ -150,7 +158,8 @@ static inline int mm_pkey_free(struct mm_struct *mm, int pkey) if (static_branch_likely(&pkey_disabled)) return -1; - if (!mm_pkey_is_allocated(mm, pkey)) + /* pkey 0 cannot be freed */ + if (!pkey || !mm_pkey_is_allocated(mm, pkey)) return -EINVAL; /*diff --git a/arch/x86/include/asm/pkeys.h b/arch/x86/include/asm/pkeys.h index a0ba1ff..6ea7486 100644 --- a/arch/x86/include/asm/pkeys.h +++ b/arch/x86/include/asm/pkeys.h@@ -52,7 +52,7 @@ bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey) * from pkey_alloc(). pkey 0 is special, and never * returned from pkey_alloc(). */ - if (pkey <= 0) + if (pkey < 0) return false; if (pkey >= arch_max_pkey()) return false;@@ -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; mm_set_pkey_free(mm, pkey);-- 1.8.3.1