On Wed, Oct 18, 2017 at 03:15:22PM +1100, Balbir Singh wrote:
> 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.
The specs says both the bits corresponding to a key are set or
reset, cannot be anything else.
cut-n-paste from the ISA...
----------------------------------------------------
Software must ensure that both bits of each even/odd
bit pair of the AMOR contain the same value. -- i.e.,
the contents of register RS for mtspr specifying the
AMOR must be such that (RS)2n = (RS)2n+1 for every
n in the range 0:31 - and like for the UAMOR.
---------------------------------------------------------
>
> > +
> > + 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>
thanks.
--
Ram Pai
