Messages in this thread | | | From | Andy Lutomirski <> | Date | Tue, 17 Jan 2017 12:29:28 -0800 | Subject | Re: [PATCHv2 3/5] x86/mm: fix native mmap() in compat bins and vice-versa |
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On Mon, Jan 16, 2017 at 4:33 AM, Dmitry Safonov <dsafonov@virtuozzo.com> wrote: > Fix 32-bit compat_sys_mmap() mapping VMA over 4Gb in 64-bit binaries > and 64-bit sys_mmap() mapping VMA only under 4Gb in 32-bit binaries. > Changed arch_get_unmapped_area{,_topdown}() to recompute mmap_base > for those cases and use according high/low limits for vm_unmapped_area() > The recomputing of mmap_base may make compat sys_mmap() in 64-bit > binaries a little slower than native, which uses already known from exec > time mmap_base - but, as it returned buggy address, that case seemed > unused previously, so no performance degradation for already used ABI.
This looks plausibly correct but rather weird -- why does this code need to distinguish between all four cases (pure 32-bit, pure 64-bit, 64-bit mmap layout doing 32-bit call, 32-bit layout doing 64-bit call)?
> Can be optimized in future by introducing mmap_compat_{,legacy}_base > in mm_struct.
Hmm. Would it make sense to do it this way from the beginning?
If adding an in_32bit_syscall() helper would help, then by all means please do so.
--Andy
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