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
