Messages in this thread | | | From | Dmitry Safonov <> | Date | Sat, 31 Dec 2016 14:10:19 +0300 | Subject | Re: [RFC 4/4] x86/arch_prctl: add ARCH_{GET,SET}_TASK_SIZE |
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Hi Andy, thanks for reviewing!
2016-12-31 5:02 GMT+03:00 Andy Lutomirski <luto@amacapital.net>: > On Fri, Dec 30, 2016 at 7:56 AM, Dmitry Safonov <dsafonov@virtuozzo.com> wrote: >> Add arch_prctl getters/setters for size of virtual address space of task. >> This adds ability to change task's virtual address space limit. >> I need this for correctly restore virtual address space limits in CRIU. >> Currently, on x86 there are three task sizes: 3GB for some old 32 bit java >> apps, 4Gb for ordinary 32-bit compatible apps and 47-bits for native >> x86_64 processes. >> 32-bit applications are restored by CRIU with the help of 64-bit clone()-d >> child, and on restore we need to place correct address space limitations >> back - otherwise 32-bit restored application may mmap() address over >> 4Gb space and as this address will not fit into 4-byte pointer, it >> will silently reuse/corrupt the pointer that has the same lower 4-bytes. >> > > I agree we need something like this, but this particular justification > is a bit bogus. If 32-bit mmap() returns an address above 2^32, then > I think it's a straight-up bug. The address space limit shouldn't > have anything to do with it -- the kernel *knows* that it's a > "compat" syscall.
Yep, I guess, I didn't realize that the real wrong thing is that compat syscall returns address above 4Gb and not the address space limits here. Thanks, will look into that.
-- Dmitry
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