linux-kernel - Re: [PATCH v4 10/17] x86/entry/64: Really create an error-entry-from-usermode code path

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Date:	Thu, 2 Jul 2015 12:25:20 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	Kees Cook <keescook@...omium.org>,
	Brian Gerst <brgerst@...il.com>, paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH v4 10/17] x86/entry/64: Really create an
 error-entry-from-usermode code path

On Mon, Jun 29, 2015 at 12:33:42PM -0700, Andy Lutomirski wrote:
> In 539f51136500 ("x86/asm/entry/64: Disentangle error_entry/exit
> gsbase/ebx/usermode code"), I arranged the code slightly wrong --
> IRET faults would skip the code path that was intended to execute on
> all error entries from user mode.  Fix it up.
> 
> This does not fix a bug, but we'll need it, and it slightly shrinks
> the code.
> 
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
>  arch/x86/entry/entry_64.S | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index 141a5d49dddc..cd9cbc62159c 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -1145,9 +1145,14 @@ ENTRY(error_entry)
>  	testb	$3, CS+8(%rsp)
>  	jz	error_kernelspace
>  
> -	/* We entered from user mode */
> +error_entry_from_usermode_swapgs:
> +	/*
> +	 * We entered from user mode or we're pretending to have entered
> +	 * from user mode due to an IRET fault.
> +	 */
>  	SWAPGS
>  
> +error_entry_from_usermode_after_swapgs:
>  error_entry_done:

Why the second label?

Also, please make all those labels local by prefixing them with .L
because they appear unnecesasrily in objdump output as global symbols.

$ objdump -d vmlinux | grep -E "^[0-9a-f]+ <(error_entry_\w*|error_kernelspace|bstep_iret|error_bad_iret)"
ffffffff8167a4a8 <error_entry_from_usermode_swapgs>:
ffffffff8167a4ab <error_entry_done>:
ffffffff8167a4b1 <error_kernelspace>:
ffffffff8167a4e0 <bstep_iret>:
ffffffff8167a4e8 <error_bad_iret>:

Oh, and shorter please :)

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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