linux-kernel - Re: [PATCH 3/4] x86: save user rsp in pt

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Message-ID: <CALCETrUJ4Db8JbRqA8pYm4V=bBG5xwm9NFmT7H0h66v68JeCGQ@mail.gmail.com>
Date:	Mon, 9 Mar 2015 13:11:02 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>, Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/4] x86: save user rsp in pt_regs->sp on SYSCALL64 fastpath

On Mon, Mar 9, 2015 at 11:39 AM, Denys Vlasenko <dvlasenk@...hat.com> wrote:
> PER_CPU(old_rsp) usage is simplified - now it is used only
> as temp storage, and userspace stack pointer is immediately stored
> in pt_regs->sp on syscall entry, instead of being used later,
> on syscall exit.
>
> Instead of PER_CPU(old_rsp) and task->thread.usersp, C code
> uses pt_regs->sp now.
>
> FIXUP/RESTORE_TOP_OF_STACK are simplified.
>
> Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
> CC: Linus Torvalds <torvalds@...ux-foundation.org>
> CC: Steven Rostedt <rostedt@...dmis.org>
> CC: Ingo Molnar <mingo@...nel.org>
> CC: Borislav Petkov <bp@...en8.de>
> CC: "H. Peter Anvin" <hpa@...or.com>
> CC: Andy Lutomirski <luto@...capital.net>
> CC: Oleg Nesterov <oleg@...hat.com>
> CC: Frederic Weisbecker <fweisbec@...il.com>
> CC: Alexei Starovoitov <ast@...mgrid.com>
> CC: Will Drewry <wad@...omium.org>
> CC: Kees Cook <keescook@...omium.org>
> CC: x86@...nel.org
> CC: linux-kernel@...r.kernel.org

Looks correct.

> @@ -253,11 +247,13 @@ GLOBAL(system_call_after_swapgs)
>          */
>         ENABLE_INTERRUPTS(CLBR_NONE)
>         ALLOC_PT_GPREGS_ON_STACK 8              /* +8: space for orig_ax */
> +       movq    %rcx,RIP(%rsp)
> +       movq    PER_CPU_VAR(old_rsp),%rcx
> +       movq    %r11,EFLAGS(%rsp)
> +       movq    %rcx,RSP(%rsp)
> +       movq_cfi rax,ORIG_RAX
>         SAVE_C_REGS_EXCEPT_RAX_RCX_R11
>         movq    $-ENOSYS,RAX(%rsp)
> -       movq_cfi rax,ORIG_RAX
> -       movq    %r11,EFLAGS(%rsp)
> -       movq    %rcx,RIP(%rsp)

Why the reordering?

--Andy
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