Messages in this thread | | | From | (Eric W. Biederman) | Date | Fri, 30 Apr 2021 14:57:43 -0500 | Subject | Re: [PATCH 2/3] arm64: signal: sigreturn() and rt_sigreturn() sometime returns the wrong signals |
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Liam Howlett <liam.howlett@oracle.com> 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
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