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powerpc: introduce execute-only pkey

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This patch provides the implementation of execute-only pkey.
The architecture-independent layer expects the arch-dependent
layer, to support the ability to create and enable a special
key which has execute-only permission.

Acked-by: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Ram Pai 2018-01-18 17:50:32 -08:00 committed by Michael Ellerman
parent 06bb53b338
commit 5586cf61e1
3 changed files with 64 additions and 1 deletions
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1
arch/powerpc/include/asm/book3s/64/mmu.h
View file

@ -116,6 +116,7 @@ typedef struct {
* bit unset -> key available for allocation
*/
u32 pkey_allocation_map;
s16 execute_only_pkey; /* key holding execute-only protection */
#endif
} mm_context_t;

6
arch/powerpc/include/asm/pkeys.h
View file

@ -117,9 +117,13 @@ static inline int mm_pkey_free(struct mm_struct *mm, int pkey)
* Try to dedicate one of the protection keys to be used as an
* execute-only protection key.
*/
extern int __execute_only_pkey(struct mm_struct *mm);
static inline int execute_only_pkey(struct mm_struct *mm)
{
return 0;
if (static_branch_likely(&pkey_disabled))
return -1;
return __execute_only_pkey(mm);
}
static inline int arch_override_mprotect_pkey(struct vm_area_struct *vma,

58
arch/powerpc/mm/pkeys.c
View file

@ -92,6 +92,8 @@ void pkey_mm_init(struct mm_struct *mm)
if (static_branch_likely(&pkey_disabled))
return;
mm_pkey_allocation_map(mm) = initial_allocation_mask;
/* -1 means unallocated or invalid */
mm->context.execute_only_pkey = -1;
}
static inline u64 read_amr(void)
@ -256,3 +258,59 @@ void thread_pkey_regs_init(struct thread_struct *thread)
write_iamr(read_iamr() & pkey_iamr_mask);
write_uamor(read_uamor() & pkey_amr_uamor_mask);
}
static inline bool pkey_allows_readwrite(int pkey)
{
int pkey_shift = pkeyshift(pkey);
if (!is_pkey_enabled(pkey))
return true;
return !(read_amr() & ((AMR_RD_BIT|AMR_WR_BIT) << pkey_shift));
}
int __execute_only_pkey(struct mm_struct *mm)
{
bool need_to_set_mm_pkey = false;
int execute_only_pkey = mm->context.execute_only_pkey;
int ret;
/* Do we need to assign a pkey for mm's execute-only maps? */
if (execute_only_pkey == -1) {
/* Go allocate one to use, which might fail */
execute_only_pkey = mm_pkey_alloc(mm);
if (execute_only_pkey < 0)
return -1;
need_to_set_mm_pkey = true;
}
/*
* We do not want to go through the relatively costly dance to set AMR
* if we do not need to. Check it first and assume that if the
* execute-only pkey is readwrite-disabled than we do not have to set it
* ourselves.
*/
if (!need_to_set_mm_pkey && !pkey_allows_readwrite(execute_only_pkey))
return execute_only_pkey;
/*
* Set up AMR so that it denies access for everything other than
* execution.
*/
ret = __arch_set_user_pkey_access(current, execute_only_pkey,
PKEY_DISABLE_ACCESS |
PKEY_DISABLE_WRITE);
/*
* If the AMR-set operation failed somehow, just return 0 and
* effectively disable execute-only support.
*/
if (ret) {
mm_pkey_free(mm, execute_only_pkey);
return -1;
}
/* We got one, store it and use it from here on out */
if (need_to_set_mm_pkey)
mm->context.execute_only_pkey = execute_only_pkey;
return execute_only_pkey;
}