Re: [RFC v2 08/12] powerpc: Handle exceptions caused by violation of pkey protection.

[Anshuman Khandual]

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@xxxxxxxxxx>
> (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 ?