[PATCH v4 15/29] arm64: handle PKEY/POE faults

[Kevin Brodsky]

On 03/05/2024 15:01, Joey Gouly wrote:
> [...]
>
> +static bool fault_from_pkey(unsigned long esr, struct vm_area_struct *vma,
> +			unsigned int mm_flags)
> +{
> +	unsigned long iss2 = ESR_ELx_ISS2(esr);
> +
> +	if (!arch_pkeys_enabled())
> +		return false;
> +
> +	if (iss2 & ESR_ELx_Overlay)
> +		return true;
> +
> +	return !arch_vma_access_permitted(vma,
> +			mm_flags & FAULT_FLAG_WRITE,
> +			mm_flags & FAULT_FLAG_INSTRUCTION,
> +			mm_flags & FAULT_FLAG_REMOTE);

This function is only called from do_page_fault(), so the access cannot
be remote. The equivalent x86 function (access_error()) always sets
foreign to false.

> +}
> +
>  static vm_fault_t __do_page_fault(struct mm_struct *mm,
>  				  struct vm_area_struct *vma, unsigned long addr,
>  				  unsigned int mm_flags, unsigned long vm_flags,
> @@ -529,6 +547,8 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
>  	unsigned int mm_flags = FAULT_FLAG_DEFAULT;
>  	unsigned long addr = untagged_addr(far);
>  	struct vm_area_struct *vma;
> +	bool pkey_fault = false;
> +	int pkey = -1;
>  
>  	if (kprobe_page_fault(regs, esr))
>  		return 0;
> @@ -590,6 +610,12 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
>  		vma_end_read(vma);
>  		goto lock_mmap;
>  	}
> +
> +	if (fault_from_pkey(esr, vma, mm_flags)) {
> +		vma_end_read(vma);
> +		goto lock_mmap;
> +	}
> +
>  	fault = handle_mm_fault(vma, addr, mm_flags | FAULT_FLAG_VMA_LOCK, regs);
>  	if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
>  		vma_end_read(vma);
> @@ -617,6 +643,11 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
>  		goto done;
>  	}
>  
> +	if (fault_from_pkey(esr, vma, mm_flags)) {
> +		pkey_fault = true;
> +		pkey = vma_pkey(vma);
> +	}
> +
>  	fault = __do_page_fault(mm, vma, addr, mm_flags, vm_flags, regs);

We don't actually need to call __do_page_fault()/handle_mm_fault() if
the fault was caused by POE. It still works since it checks
arch_vma_access_permitted() early, but we might as well skip it
altogether (like on x86). On 6.10-rcX, we could handle it like a missing
vm_flags (goto bad_area).

Kevin