Re: [PATCHv8 1/2] x86/vdso: add mremap hook to vm_special_mapping

From: Dmitry Safonov
Date: Thu May 05 2016 - 07:56:38 EST

On 05/05/2016 02:52 PM, Ingo Molnar wrote:

* Dmitry Safonov <dsafonov@xxxxxxxxxxxxx> wrote:

On 04/26/2016 12:38 AM, Andy Lutomirski wrote:
On Mon, Apr 25, 2016 at 4:37 AM, Dmitry Safonov <dsafonov@xxxxxxxxxxxxx> 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/
Acked-by: Andy Lutomirski <luto@xxxxxxxxxx>

Ingo, can you apply this?

Hm, so I'm not sure - should I resend those two?
Or just ping?

Please send a clean series with updated Acked-by's, etc.

Thanks, Ingo, will do.
Sorry for html in the last email - mail agent got an
update and I overlooked html composing become turned on.

Dmitry Safonov