On Fri, 8 Sep 2017 15:44:59 -0700
Ram Pai <linux...@us.ibm.com> wrote:
> 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.
>
> Signed-off-by: Ram Pai <linux...@us.ibm.com>
> ---
> arch/powerpc/include/asm/book3s/64/mmu.h | 1 +
> arch/powerpc/include/asm/pkeys.h | 9 ++++-
> arch/powerpc/mm/pkeys.c | 57
> ++++++++++++++++++++++++++++++
> 3 files changed, 66 insertions(+), 1 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h
> b/arch/powerpc/include/asm/book3s/64/mmu.h
> index 55950f4..ee18ba0 100644
> --- a/arch/powerpc/include/asm/book3s/64/mmu.h
> +++ b/arch/powerpc/include/asm/book3s/64/mmu.h
> @@ -115,6 +115,7 @@ struct patb_entry {
> * bit unset -> key available for allocation
> */
> u32 pkey_allocation_map;
> + s16 execute_only_pkey; /* key holding execute-only protection */
> #endif
> } mm_context_t;
>
> diff --git a/arch/powerpc/include/asm/pkeys.h
> b/arch/powerpc/include/asm/pkeys.h
> index 78c5362..0cf115f 100644
> --- a/arch/powerpc/include/asm/pkeys.h
> +++ b/arch/powerpc/include/asm/pkeys.h
> @@ -115,11 +115,16 @@ 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 (!pkey_inited || !pkey_execute_disable_support)
> + return -1;
> +
> + return __execute_only_pkey(mm);
> }
>
> +
> static inline int arch_override_mprotect_pkey(struct vm_area_struct *vma,
> int prot, int pkey)
> {
> @@ -141,6 +146,8 @@ static inline void pkey_mm_init(struct mm_struct *mm)
> if (!pkey_inited)
> return;
> mm_pkey_allocation_map(mm) = initial_allocation_mask;
> + /* -1 means unallocated or invalid */
> + mm->context.execute_only_pkey = -1;
> }
>
> extern void thread_pkey_regs_save(struct thread_struct *thread);
> diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
> index 7cd1be4..8a24983 100644
> --- a/arch/powerpc/mm/pkeys.c
> +++ b/arch/powerpc/mm/pkeys.c
> @@ -188,3 +188,60 @@ void thread_pkey_regs_init(struct thread_struct *thread)
> write_iamr(0x0ul);
> write_uamor(0x0ul);
> }
> +
> +static inline bool pkey_allows_readwrite(int pkey)
> +{
> + int pkey_shift = pkeyshift(pkey);
> +
> + if (!(read_uamor() & (0x3UL << pkey_shift)))
> + return true;
If uamor for key 0 is 0x10 for example or 0x01 it's a bug.
The above check might miss it.
> +
> + 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_set_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;
> +}
Looks good otherwise
Acked-by: Balbir Singh <bsinghar...@gmail.com>
