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Message-Id: <20170713074500.GF5525@ram.oc3035372033.ibm.com>
Date: Thu, 13 Jul 2017 00:45:00 -0700
From: Ram Pai <linuxram@...ibm.com>
To: Balbir Singh <bsingharora@...il.com>
Cc: linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
linux-arch@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org,
benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au,
khandual@...ux.vnet.ibm.com, aneesh.kumar@...ux.vnet.ibm.com,
dave.hansen@...el.com, hbabu@...ibm.com, arnd@...db.de,
akpm@...ux-foundation.org, corbet@....net, mingo@...hat.com
Subject: Re: [RFC v5 14/38] powerpc: initial plumbing for key management
On Wed, Jul 12, 2017 at 01:28:25PM +1000, Balbir Singh wrote:
> On Wed, 5 Jul 2017 14:21:51 -0700
> Ram Pai <linuxram@...ibm.com> 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?
It works in supervisor mode, as a guest aswell as a bare-metal
kernel. Whatever needs to be done in hypervisor mode
is already there in power-kvm.
>
> >
> > Also it adds skeletal functions and macros, that the
> > architecture-independent code expects to be available.
> >
> > Signed-off-by: Ram Pai <linuxram@...ibm.com>
> > ---
> > 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?
Yes. Was one of my TODOs to initilize this using the device-tree
interface. A brief look at that did not show the reserved keys
properly enumerated. But I may be wrong.
>
> > +
> > +#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?
yes.
>
> > +
> > +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?
ok.
>
> > +#endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
> > +
> > return index;
> > }
> >
>
> Balbir Singh.
--
Ram Pai
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