Re: [RFC v5 14/38] powerpc: initial plumbing for key management

[Balbir Singh]

On Wed,  5 Jul 2017 14:21:51 -0700
Ram Pai <linuxram@xxxxxxxxxx> wrote:

> Initial plumbing to manage all the keys supported by the
> hardware.
> 
> Total 32 keys are supported on powerpc. However pkey 0,1
> and 31 are reserved. So effectively we have 29 pkeys.
> 
> This patch keeps track of reserved keys, allocated  keys
> and keys that are currently free.

It looks like this patch will only work in guest mode?
Is that an assumption we've made? What happens if I use
keys when running in hypervisor mode?

> 
> Also it  adds  skeletal  functions  and macros, that the
> architecture-independent code expects to be available.
> 
> Signed-off-by: Ram Pai <linuxram@xxxxxxxxxx>
> ---
>  arch/powerpc/Kconfig                     |   16 +++++
>  arch/powerpc/include/asm/book3s/64/mmu.h |    9 +++
>  arch/powerpc/include/asm/pkeys.h         |  106 ++++++++++++++++++++++++++++++
>  arch/powerpc/mm/mmu_context_book3s64.c   |    5 ++
>  4 files changed, 136 insertions(+), 0 deletions(-)
>  create mode 100644 arch/powerpc/include/asm/pkeys.h
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index f7c8f99..a2480b6 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -871,6 +871,22 @@ config SECCOMP
>  
>  	  If unsure, say Y. Only embedded should say N here.
>  
> +config PPC64_MEMORY_PROTECTION_KEYS
> +	prompt "PowerPC Memory Protection Keys"
> +	def_bool y
> +	# Note: only available in 64-bit mode
> +	depends on PPC64 && PPC_64K_PAGES
> +	select ARCH_USES_HIGH_VMA_FLAGS
> +	select ARCH_HAS_PKEYS
> +	---help---
> +	  Memory Protection Keys provides a mechanism for enforcing
> +	  page-based protections, but without requiring modification of the
> +	  page tables when an application changes protection domains.
> +
> +	  For details, see Documentation/powerpc/protection-keys.txt
> +
> +	  If unsure, say y.
> +
>  endmenu
>  
>  config ISA_DMA_API
> diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h b/arch/powerpc/include/asm/book3s/64/mmu.h
> index 77529a3..104ad72 100644
> --- a/arch/powerpc/include/asm/book3s/64/mmu.h
> +++ b/arch/powerpc/include/asm/book3s/64/mmu.h
> @@ -108,6 +108,15 @@ struct patb_entry {
>  #ifdef CONFIG_SPAPR_TCE_IOMMU
>  	struct list_head iommu_group_mem_list;
>  #endif
> +
> +#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
> +	/*
> +	 * Each bit represents one protection key.
> +	 * bit set   -> key allocated
> +	 * bit unset -> key available for allocation
> +	 */
> +	u32 pkey_allocation_map;
> +#endif
>  } mm_context_t;
>  
>  /*
> diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h
> new file mode 100644
> index 0000000..9345767
> --- /dev/null
> +++ b/arch/powerpc/include/asm/pkeys.h
> @@ -0,0 +1,106 @@
> +#ifndef _ASM_PPC64_PKEYS_H
> +#define _ASM_PPC64_PKEYS_H
> +
> +#define arch_max_pkey()  32
> +#define ARCH_VM_PKEY_FLAGS (VM_PKEY_BIT0 | VM_PKEY_BIT1 | VM_PKEY_BIT2 | \
> +				VM_PKEY_BIT3 | VM_PKEY_BIT4)
> +/*
> + * Bits are in BE format.
> + * NOTE: key 31, 1, 0 are not used.
> + * key 0 is used by default. It give read/write/execute permission.
> + * key 31 is reserved by the hypervisor.
> + * key 1 is recommended to be not used.
> + * PowerISA(3.0) page 1015, programming note.
> + */
> +#define PKEY_INITIAL_ALLOCAION  0xc0000001

Shouldn't this be exchanged via CAS for guests? Have you seen
ibm,processor-storage-keys?

> +
> +#define pkeybit_mask(pkey) (0x1 << (arch_max_pkey() - pkey - 1))
> +
> +#define mm_pkey_allocation_map(mm)	(mm->context.pkey_allocation_map)
> +
> +#define mm_set_pkey_allocated(mm, pkey) {	\
> +	mm_pkey_allocation_map(mm) |= pkeybit_mask(pkey); \
> +}
> +
> +#define mm_set_pkey_free(mm, pkey) {	\
> +	mm_pkey_allocation_map(mm) &= ~pkeybit_mask(pkey);	\
> +}
> +
> +#define mm_set_pkey_is_allocated(mm, pkey)	\
> +	(mm_pkey_allocation_map(mm) & pkeybit_mask(pkey))
> +
> +#define mm_set_pkey_is_reserved(mm, pkey) (PKEY_INITIAL_ALLOCAION & \
> +					pkeybit_mask(pkey))
> +
> +static inline bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey)
> +{
> +	/* a reserved key is never considered as 'explicitly allocated' */
> +	return (!mm_set_pkey_is_reserved(mm, pkey) &&
> +		mm_set_pkey_is_allocated(mm, pkey));
> +}
> +
> +/*
> + * Returns a positive, 5-bit key on success, or -1 on failure.
> + */
> +static inline int mm_pkey_alloc(struct mm_struct *mm)
> +{
> +	/*
> +	 * Note: this is the one and only place we make sure
> +	 * that the pkey is valid as far as the hardware is
> +	 * concerned.  The rest of the kernel trusts that
> +	 * only good, valid pkeys come out of here.
> +	 */
> +	u32 all_pkeys_mask = (u32)(~(0x0));
> +	int ret;
> +
> +	/*
> +	 * Are we out of pkeys?  We must handle this specially
> +	 * because ffz() behavior is undefined if there are no
> +	 * zeros.
> +	 */
> +	if (mm_pkey_allocation_map(mm) == all_pkeys_mask)
> +		return -1;
> +
> +	ret = arch_max_pkey() -
> +		ffz((u32)mm_pkey_allocation_map(mm))
> +		- 1;
> +	mm_set_pkey_allocated(mm, ret);
> +	return ret;
> +}

So the locking is provided by the caller for the function above?

> +
> +static inline int mm_pkey_free(struct mm_struct *mm, int pkey)
> +{
> +	if (!mm_pkey_is_allocated(mm, pkey))
> +		return -EINVAL;
> +
> +	mm_set_pkey_free(mm, pkey);
> +
> +	return 0;
> +}
> +
> +/*
> + * Try to dedicate one of the protection keys to be used as an
> + * execute-only protection key.
> + */
> +static inline int execute_only_pkey(struct mm_struct *mm)
> +{
> +	return 0;
> +}
> +
> +static inline int arch_override_mprotect_pkey(struct vm_area_struct *vma,
> +		int prot, int pkey)
> +{
> +	return 0;
> +}
> +
> +static inline int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
> +		unsigned long init_val)
> +{
> +	return 0;
> +}
> +
> +static inline void pkey_mm_init(struct mm_struct *mm)
> +{
> +	mm_pkey_allocation_map(mm) = PKEY_INITIAL_ALLOCAION;
> +}
> +#endif /*_ASM_PPC64_PKEYS_H */
> diff --git a/arch/powerpc/mm/mmu_context_book3s64.c b/arch/powerpc/mm/mmu_context_book3s64.c
> index c6dca2a..2da9931 100644
> --- a/arch/powerpc/mm/mmu_context_book3s64.c
> +++ b/arch/powerpc/mm/mmu_context_book3s64.c
> @@ -16,6 +16,7 @@
>  #include <linux/string.h>
>  #include <linux/types.h>
>  #include <linux/mm.h>
> +#include <linux/pkeys.h>
>  #include <linux/spinlock.h>
>  #include <linux/idr.h>
>  #include <linux/export.h>
> @@ -120,6 +121,10 @@ static int hash__init_new_context(struct mm_struct *mm)
>  
>  	subpage_prot_init_new_context(mm);
>  
> +#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
> +	pkey_mm_init(mm);

Can we have two variants of pkey_mm_init() and avoid #ifdefs around the code?

> +#endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
> +
>  	return index;
>  }
>  

Balbir Singh.