Liam Howlett <liam.howlett@xxxxxxxxxx> writes:
> This is way out of scope for what I'm doing. I'm trying to fix a call
> to the wrong mm API. I was trying to clean up any obvious errors in
> calling functions which were exposed by fixing that error. If you want
> this fixed differently, then please go ahead and tackle the problems you
> see.
I was asked by the arm maintainers to describe what the code should be
doing here. I hope I have done that.
What is very interesting is that the code in __do_page_fault does not
use find_vma_intersection it uses find_vma. Which suggests that
find_vma_intersection may not be the proper mm api.
The logic is:
>From __do_page_fault:
struct vm_area_struct *vma = find_vma(mm, addr);
if (unlikely(!vma))
return VM_FAULT_BADMAP;
/*
* Ok, we have a good vm_area for this memory access, so we can handle
* it.
*/
if (unlikely(vma->vm_start > addr)) {
if (!(vma->vm_flags & VM_GROWSDOWN))
return VM_FAULT_BADMAP;
if (expand_stack(vma, addr))
return VM_FAULT_BADMAP;
}
/*
* Check that the permissions on the VMA allow for the fault which
* occurred.
*/
if (!(vma->vm_flags & vm_flags))
return VM_FAULT_BADACCESS;
>From do_page_fault:
arm64_force_sig_fault(SIGSEGV,
fault == VM_FAULT_BADACCESS ? SEGV_ACCERR : SEGV_MAPERR,
far, inf->name);
Hmm. If the expand_stack step is skipped. Does is the logic equivalent
to find_vma_intersection?
static inline struct vm_area_struct *find_vma_intersection(
struct mm_struct * mm,
unsigned long start_addr,
unsigned long end_addr)
{
struct vm_area_struct * vma = find_vma(mm,start_addr);
if (vma && end_addr <= vma->vm_start)
vma = NULL;
return vma;
}
Yes. It does look that way. VM_FAULT_BADMAP is returned when a vma
covering the specified address is not found. And VM_FAULT_BADACCESS is
returned when there is a vma and there is a permission problem.
There are also two SIGBUS cases that arm64_notify_segfault does not
handle.
So it appears changing arm64_notify_segfault to use
find_vma_intersection instead of find_vma would be a correct but
incomplete fix.
I don't see a point in changing sigerturn or rt_sigreturn.
Eric
