linux-kernel - Re: [GIT PULL] x86: unify sys

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Date:	Fri, 25 Sep 2009 18:56:38 -0400
From:	Brian Gerst <brgerst@...il.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Ingo Molnar <mingo@...hat.com>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] x86: unify sys_iopl

The correct fix is to move set_iopl_mask into do_iopl.  sys_iopl
should only be a wrapper around do_iopl to manage the different
calling convention used by 32-bit and 64-bit.

On Fri, Sep 25, 2009 at 6:05 PM, Jeremy Fitzhardinge <jeremy@...p.org> wrote:
> Hi Ingo,
>
> The x86-64 implementation of iopl was buggy because it never ended up calling
> set_iopl_mask().  This had no effect on native sys_iopl (because set_iopl_mask
> is normally no-op on 64-bit), but it ended up never calling the pvop, which caused
> iopl to have no effect on 64-bit Xen guests.
>
> The two functions are needlessly different anyway.  This patch just unifies them
> into a single function which is mostly derived from the 32-bit version.
>
> Thanks,
>        J
>
> The following changes since commit c44c9ec0f38b939b3200436e3aa95c1aa83c41c7:
>  Jeremy Fitzhardinge (1):
>        x86: split NX setup into separate file to limit unstack-protected code
>
> are available in the git repository at:
>
>  git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen.git bugfix
>
> Jeremy Fitzhardinge (1):
>      x86: unify sys_iopl
>
>  arch/x86/include/asm/syscalls.h |    8 +++-----
>  arch/x86/kernel/ioport.c        |   11 ++---------
>  2 files changed, 5 insertions(+), 14 deletions(-)
>
> From 8dbb1d168eb8be6bf43d123fdfb3ba3b03762e62 Mon Sep 17 00:00:00 2001
> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
> Date: Wed, 23 Sep 2009 16:35:24 -0700
> Subject: [PATCH] x86: unify sys_iopl
>
> The 32 and 64-bit versions of sys_iopl were needlessly different:
>  - The 32-bit version ignored its function argument and directly
>   fetched the parameter from struct regs, presumably code dating
>   from the neolithic era.
>  - The 64-bit version never called set_iopl_mask().  Usually this
>   is a no-op for 64-bit, but it is also a pvop, which meant that
>   that iopl never worked for 64-bit guests under Xen.
>  - Both versions use the archaic style of getting pt_regs passed
>   to them.  We can get the current pt_regs with task_pt_regs, which
>   avoids worrying about the fine details of stack layout.
>
> We can use the body of the 32-bit function with a few small
> adjustments to the function definition.
>
> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
>
> diff --git a/arch/x86/include/asm/syscalls.h b/arch/x86/include/asm/syscalls.h
> index 372b76e..5336ce2 100644
> --- a/arch/x86/include/asm/syscalls.h
> +++ b/arch/x86/include/asm/syscalls.h
> @@ -33,11 +33,11 @@ long sys_rt_sigreturn(struct pt_regs *);
>  asmlinkage int sys_set_thread_area(struct user_desc __user *);
>  asmlinkage int sys_get_thread_area(struct user_desc __user *);
>
> -/* X86_32 only */
> -#ifdef CONFIG_X86_32
>  /* kernel/ioport.c */
> -long sys_iopl(struct pt_regs *);
> +asmlinkage long sys_iopl(unsigned int);
>
> +/* X86_32 only */
> +#ifdef CONFIG_X86_32
>  /* kernel/process_32.c */
>  int sys_clone(struct pt_regs *);
>  int sys_execve(struct pt_regs *);
> @@ -70,8 +70,6 @@ int sys_vm86(struct pt_regs *);
>  #else /* CONFIG_X86_32 */
>
>  /* X86_64 only */
> -/* kernel/ioport.c */
> -asmlinkage long sys_iopl(unsigned int, struct pt_regs *);
>
>  /* kernel/process_64.c */
>  asmlinkage long sys_clone(unsigned long, unsigned long,
> diff --git a/arch/x86/kernel/ioport.c b/arch/x86/kernel/ioport.c
> index 99c4d30..bad4f22 100644
> --- a/arch/x86/kernel/ioport.c
> +++ b/arch/x86/kernel/ioport.c
> @@ -119,11 +119,10 @@ static int do_iopl(unsigned int level, struct pt_regs *regs)
>        return 0;
>  }
>
> -#ifdef CONFIG_X86_32
> -long sys_iopl(struct pt_regs *regs)
> +asmlinkage long sys_iopl(unsigned int level)
>  {
> -       unsigned int level = regs->bx;
>        struct thread_struct *t = &current->thread;
> +       struct pt_regs *regs = task_pt_regs(current);
>        int rc;
>
>        rc = do_iopl(level, regs);
> @@ -135,9 +134,3 @@ long sys_iopl(struct pt_regs *regs)
>  out:
>        return rc;
>  }
> -#else
> -asmlinkage long sys_iopl(unsigned int level, struct pt_regs *regs)
> -{
> -       return do_iopl(level, regs);
> -}
> -#endif
>
>
> --
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