linux-kernel - Re: [PATCHv10 1/2] x86/vdso: add mremap hook to vm_special

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Date:	Wed, 6 Jul 2016 07:03:48 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Dmitry Safonov <dsafonov@...tuozzo.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Dmitry Safonov <0x7f454c46@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Lutomirski <luto@...nel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>
Subject: Re: [PATCHv10 1/2] x86/vdso: add mremap hook to vm_special_mapping

On Tue, Jun 28, 2016 at 4:35 AM, Dmitry Safonov <dsafonov@...tuozzo.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

Acked-by: Andy Lutomirski <luto@...nel.org>