linux-kernel - Re: [patch V2 14/16] x86/iopl: Restrict iopl() permission scope

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Date:   Tue, 12 Nov 2019 07:32:52 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Willy Tarreau <w@....eu>, Juergen Gross <jgross@...e.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [patch V2 14/16] x86/iopl: Restrict iopl() permission scope


* Thomas Gleixner <tglx@...utronix.de> wrote:

> --- a/arch/x86/kernel/ioport.c
> +++ b/arch/x86/kernel/ioport.c
> @@ -18,12 +18,15 @@ static atomic64_t io_bitmap_sequence;
>  
>  void io_bitmap_share(struct task_struct *tsk)
>   {
> -	/*
> -	 * Take a refcount on current's bitmap. It can be used by
> -	 * both tasks as long as none of them changes the bitmap.
> -	 */
> -	refcount_inc(&current->thread.io_bitmap->refcnt);
> -	tsk->thread.io_bitmap = current->thread.io_bitmap;
> +	 /* Can be NULL when current->thread.iopl_emul == 3 */
> +	 if (current->thread.io_bitmap) {
> +		 /*
> +		  * Take a refcount on current's bitmap. It can be used by
> +		  * both tasks as long as none of them changes the bitmap.
> +		  */
> +		 refcount_inc(&current->thread.io_bitmap->refcnt);
> +		 tsk->thread.io_bitmap = current->thread.io_bitmap;
> +	 }

Minor side note: whitespace damage managed to slip in that code, see the 
fix below.

Thanks,

	Ingo

 arch/x86/kernel/ioport.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/ioport.c b/arch/x86/kernel/ioport.c
index f87844e22ec9..ee37a1c25ecc 100644
--- a/arch/x86/kernel/ioport.c
+++ b/arch/x86/kernel/ioport.c
@@ -17,16 +17,16 @@
 static atomic64_t io_bitmap_sequence;
 
 void io_bitmap_share(struct task_struct *tsk)
- {
-	 /* Can be NULL when current->thread.iopl_emul == 3 */
-	 if (current->thread.io_bitmap) {
-		 /*
-		  * Take a refcount on current's bitmap. It can be used by
-		  * both tasks as long as none of them changes the bitmap.
-		  */
-		 refcount_inc(&current->thread.io_bitmap->refcnt);
-		 tsk->thread.io_bitmap = current->thread.io_bitmap;
-	 }
+{
+	/* Can be NULL when current->thread.iopl_emul == 3 */
+	if (current->thread.io_bitmap) {
+		/*
+		 * Take a refcount on current's bitmap. It can be used by
+		 * both tasks as long as none of them changes the bitmap.
+		 */
+		refcount_inc(&current->thread.io_bitmap->refcnt);
+		tsk->thread.io_bitmap = current->thread.io_bitmap;
+	}
 	set_tsk_thread_flag(tsk, TIF_IO_BITMAP);
 }