Messages in this thread |  | | Date | Tue, 14 Nov 2017 13:11:41 +0100 (CET) | | From | Thomas Gleixner <> | | Subject | Re: [PATCH] x86/mm: Do not allow non-MAP_FIXED mapping across DEFAULT_MAP_WINDOW border |
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On Tue, 14 Nov 2017, Kirill A. Shutemov wrote: > On Mon, Nov 13, 2017 at 10:14:36PM +0100, Thomas Gleixner wrote: > > I can see where you are heading to. Now the case I was looking at is: > > > > arch_get_unmapped_area_topdown() > > > > addr0 = addr; > > > > .... > > if (addr) { > > if (cross_border(addr, len)) > > goto get_unmapped_area; > > ... > > } > > get_unmapped_area: > > ... > > if (addr > DEFAULT_MAP_WINDOW && !in_compat_syscall()) > > > > ^^^ evaluates to false because addr < DEFAULT_MAP_WINDOW > > > > addr - vm_unmapped_area(&info); > > > > ^^^ fails for whatever reason. > > > > bottomup: > > return arch_get_unmapped_area(.., addr0, len, ....); > > > > > > AFAICT arch_get_unmapped_area() can allocate a mapping which crosses the > > border, i.e. a mapping which you want to prevent for the !MAP_FIXED case. > > No, it can't as long as addr0 is below DEFAULT_MAP_WINDOW: > > arch_get_unmapped_area() > { > ... > find_start_end(addr, flags, &begin, &end); > // end is DEFAULT_MAP_WINDOW here, since addr is below the border
Sigh, I missed that task_size_64bit() magic in find_start_end().
This is really convoluted and non intuitive. I'm so not looking forward to debug any failure in that context.
Thanks,
tglx
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