Re: [PATCHv10 1/2] x86/vdso: add mremap hook to vm_special_mapping

Andy Lutomirski
2016-07-06T14:04:32Z

On Tue, Jun 28, 2016 at 4:35 AM, Dmitry Safonov <dsafonov@virtuozzo.com> wrote:
> Add possibility for userspace 32-bit applications to move
> vdso mapping. Previously, when userspace app called
> mremap for vdso, in return path it would land on previous
> address of vdso page, resulting in segmentation violation.
> Now it lands fine and returns to userspace with remapped vdso.
> This will also fix context.vdso pointer for 64-bit, which does not
> affect the user of vdso after mremap by now, but this may change.
>
> As suggested by Andy, return EINVAL for mremap that splits vdso image.
>
> Renamed and moved text_mapping structure declaration inside
> map_vdso, as it used only there and now it complement
> vvar_mapping variable.
>
> There is still problem for remapping vdso in glibc applications:
> linker relocates addresses for syscalls on vdso page, so
> you need to relink with the new addresses. Or the next syscall
> through glibc may fail:
> Program received signal SIGSEGV, Segmentation fault.
> #0 0xf7fd9b80 in __kernel_vsyscall ()
> #1 0xf7ec8238 in _exit () from /usr/lib32/libc.so.6