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Commit 5586cf61 authored by Ram Pai's avatar Ram Pai Committed by Michael Ellerman
Browse files

powerpc: introduce execute-only pkey 



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: default avatarBalbir Singh <bsingharora@gmail.com>
Signed-off-by: default avatarRam Pai <linuxram@us.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent 06bb53b3

arch/powerpc/include/asm/book3s/64/mmu.h

+1 −0
Original line number Diff line number Diff line
@@ -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;

arch/powerpc/include/asm/pkeys.h

+5 −1
Original line number Diff line number Diff line
@@ -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,

arch/powerpc/mm/pkeys.c

+58 −0
Original line number Diff line number Diff line
@@ -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;

}