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Message-Id: <a288b72b-3e9c-7bf9-fff4-e5b08bad0374@linux.vnet.ibm.com>
Date: Tue, 20 Jun 2017 12:54:45 +0530
From: Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To: Ram Pai <linuxram@...ibm.com>, linuxppc-dev@...ts.ozlabs.org,
linux-kernel@...r.kernel.org
Cc: dave.hansen@...el.com, paulus@...ba.org,
aneesh.kumar@...ux.vnet.ibm.com
Subject: Re: [RFC v2 08/12] powerpc: Handle exceptions caused by violation of
pkey protection.
On 06/17/2017 09:22 AM, Ram Pai wrote:
> Handle Data and Instruction exceptions caused by memory
> protection-key.
>
> Signed-off-by: Ram Pai <linuxram@...ibm.com>
> (cherry picked from commit a5e5217619a0c475fe0cacc3b0cf1d3d33c79a09)
To which tree this commit belongs to ?
>
> Conflicts:
> arch/powerpc/include/asm/reg.h
> arch/powerpc/kernel/exceptions-64s.S
> ---
> arch/powerpc/include/asm/mmu_context.h | 12 +++++
> arch/powerpc/include/asm/pkeys.h | 9 ++++
> arch/powerpc/include/asm/reg.h | 7 +--
> arch/powerpc/mm/fault.c | 21 +++++++-
> arch/powerpc/mm/pkeys.c | 90 ++++++++++++++++++++++++++++++++++
> 5 files changed, 134 insertions(+), 5 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
> index da7e943..71fffe0 100644
> --- a/arch/powerpc/include/asm/mmu_context.h
> +++ b/arch/powerpc/include/asm/mmu_context.h
> @@ -175,11 +175,23 @@ static inline void arch_bprm_mm_init(struct mm_struct *mm,
> {
> }
>
> +#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
> +bool arch_pte_access_permitted(pte_t pte, bool write);
> +bool arch_vma_access_permitted(struct vm_area_struct *vma,
> + bool write, bool execute, bool foreign);
> +#else /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
> +static inline bool arch_pte_access_permitted(pte_t pte, bool write)
> +{
> + /* by default, allow everything */
> + return true;
> +}
> static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
> bool write, bool execute, bool foreign)
> {
> /* by default, allow everything */
> return true;
> }
Right, these are the two functions the core VM expects the
arch to provide.
> +#endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
> +
> #endif /* __KERNEL__ */
> #endif /* __ASM_POWERPC_MMU_CONTEXT_H */
> diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h
> index 9b6820d..405e7db 100644
> --- a/arch/powerpc/include/asm/pkeys.h
> +++ b/arch/powerpc/include/asm/pkeys.h
> @@ -14,6 +14,15 @@
> VM_PKEY_BIT3 | \
> VM_PKEY_BIT4)
>
> +static inline u16 pte_flags_to_pkey(unsigned long pte_flags)
> +{
> + return ((pte_flags & H_PAGE_PKEY_BIT4) ? 0x1 : 0x0) |
> + ((pte_flags & H_PAGE_PKEY_BIT3) ? 0x2 : 0x0) |
> + ((pte_flags & H_PAGE_PKEY_BIT2) ? 0x4 : 0x0) |
> + ((pte_flags & H_PAGE_PKEY_BIT1) ? 0x8 : 0x0) |
> + ((pte_flags & H_PAGE_PKEY_BIT0) ? 0x10 : 0x0);
> +}
Add defines for the above 0x1, 0x2, 0x4, 0x8 etc ?
> +
> #define pkey_to_vmflag_bits(key) (((key & 0x1UL) ? VM_PKEY_BIT0 : 0x0UL) | \
> ((key & 0x2UL) ? VM_PKEY_BIT1 : 0x0UL) | \
> ((key & 0x4UL) ? VM_PKEY_BIT2 : 0x0UL) | \
> diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
> index 2dcb8a1..a11977f 100644
> --- a/arch/powerpc/include/asm/reg.h
> +++ b/arch/powerpc/include/asm/reg.h
> @@ -285,9 +285,10 @@
> #define DSISR_UNSUPP_MMU 0x00080000 /* Unsupported MMU config */
> #define DSISR_SET_RC 0x00040000 /* Failed setting of R/C bits */
> #define DSISR_PGDIRFAULT 0x00020000 /* Fault on page directory */
> -#define DSISR_PAGE_FAULT_MASK (DSISR_BIT32 | \
> - DSISR_PAGEATTR_CONFLT | \
> - DSISR_BADACCESS | \
> +#define DSISR_PAGE_FAULT_MASK (DSISR_BIT32 | \
> + DSISR_PAGEATTR_CONFLT | \
> + DSISR_BADACCESS | \
> + DSISR_KEYFAULT | \
> DSISR_BIT43)
This should have been cleaned up before adding new
DSISR_KEYFAULT reason code into it. But I guess its
okay.
> #define SPRN_TBRL 0x10C /* Time Base Read Lower Register (user, R/O) */
> #define SPRN_TBRU 0x10D /* Time Base Read Upper Register (user, R/O) */
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index 3a7d580..c31624f 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -216,9 +216,10 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
> * bits we are interested in. But there are some bits which
> * indicate errors in DSISR but can validly be set in SRR1.
> */
> - if (trap == 0x400)
> + if (trap == 0x400) {
> error_code &= 0x48200000;
> - else
> + flags |= FAULT_FLAG_INSTRUCTION;
> + } else
> is_write = error_code & DSISR_ISSTORE;
> #else
Why adding the FAULT_FLAG_INSTRUCTION here ?
> is_write = error_code & ESR_DST;
> @@ -261,6 +262,13 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
> }
> #endif
>
> +#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
> + if (error_code & DSISR_KEYFAULT) {
> + code = SEGV_PKUERR;
> + goto bad_area_nosemaphore;
> + }
> +#endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
> +
> /* We restore the interrupt state now */
> if (!arch_irq_disabled_regs(regs))
> local_irq_enable();
> @@ -441,6 +449,15 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
> WARN_ON_ONCE(error_code & DSISR_PROTFAULT);
> #endif /* CONFIG_PPC_STD_MMU */
>
> +#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
> + if (!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE,
> + flags & FAULT_FLAG_INSTRUCTION,
> + 0)) {
> + code = SEGV_PKUERR;
> + goto bad_area;
> + }
> +#endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
> +
I am wondering why both the above checks are required ?
* DSISR should contains DSISR_KEYFAULT
* VMA pkey values whether they matched the fault cause
> /*
> * If for any reason at all we couldn't handle the fault,
> * make sure we exit gracefully rather than endlessly redo
> diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
> index 11a32b3..439241a 100644
> --- a/arch/powerpc/mm/pkeys.c
> +++ b/arch/powerpc/mm/pkeys.c
> @@ -27,6 +27,37 @@ static inline bool pkey_allows_readwrite(int pkey)
> return !(read_amr() & ((AMR_AD_BIT|AMR_WD_BIT) << pkey_shift));
> }
>
> +static inline bool pkey_allows_read(int pkey)
> +{
> + int pkey_shift = (arch_max_pkey()-pkey-1) * AMR_BITS_PER_PKEY;
> +
> + if (!(read_uamor() & (0x3ul << pkey_shift)))
> + return true;
> +
> + return !(read_amr() & (AMR_AD_BIT << pkey_shift));
> +}
Get read_amr() into a local variable and save some cycles if we
have to do it again.
> +
> +static inline bool pkey_allows_write(int pkey)
> +{
> + int pkey_shift = (arch_max_pkey()-pkey-1) * AMR_BITS_PER_PKEY;
> +
> + if (!(read_uamor() & (0x3ul << pkey_shift)))
> + return true;
> +
> + return !(read_amr() & (AMR_WD_BIT << pkey_shift));
> +}
> +
Ditto
> +static inline bool pkey_allows_execute(int pkey)
> +{
> + int pkey_shift = (arch_max_pkey()-pkey-1) * AMR_BITS_PER_PKEY;
> +
> + if (!(read_uamor() & (0x3ul << pkey_shift)))
> + return true;
> +
> + return !(read_iamr() & (IAMR_EX_BIT << pkey_shift));
> +}
Ditto
> +
> +
> /*
> * set the access right in AMR IAMR and UAMOR register
> * for @pkey to that specified in @init_val.
> @@ -175,3 +206,62 @@ int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot,
> */
> return vma_pkey(vma);
> }
> +
> +bool arch_pte_access_permitted(pte_t pte, bool write)
> +{
> + int pkey = pte_flags_to_pkey(pte_val(pte));
> +
> + if (!pkey_allows_read(pkey))
> + return false;
> + if (write && !pkey_allows_write(pkey))
> + return false;
> + return true;
> +}
> +
> +/*
> + * We only want to enforce protection keys on the current process
> + * because we effectively have no access to AMR/IAMR for other
> + * processes or any way to tell *which * AMR/IAMR in a threaded
> + * process we could use.
> + *
> + * So do not enforce things if the VMA is not from the current
> + * mm, or if we are in a kernel thread.
> + */
> +static inline bool vma_is_foreign(struct vm_area_struct *vma)
> +{
> + if (!current->mm)
> + return true;
> + /*
> + * if the VMA is from another process, then AMR/IAMR has no
> + * relevance and should not be enforced.
> + */
> + if (current->mm != vma->vm_mm)
> + return true;
> +
> + return false;
> +}
> +
This seems pretty generic, should not be moved to core MM ?
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