linux-kernel - Re: [PATCH v4 07/17] x86/traps: Assert that we're in CONTEXT

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Date:	Tue, 30 Jun 2015 19:01:04 +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 07/17] x86/traps: Assert that we're in CONTEXT_KERNEL
 in exception entries

On Mon, Jun 29, 2015 at 12:33:39PM -0700, Andy Lutomirski wrote:
> Other than the super-atomic exception entries, all exception entries
> are supposed to switch our context tracking state to CONTEXT_KERNEL.
> Assert that they do.  These assertions appear trivial at this point,
> as exception_enter is the function responsible for switching
> context, but I'm planning on reworking x86's exception context
> tracking, and these assertions will help make sure that all of this
> code keeps working.
> 
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
>  arch/x86/kernel/traps.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index f5791927aa64..2a783c4fe0e9 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -292,6 +292,8 @@ static void do_error_trap(struct pt_regs *regs, long error_code, char *str,
>  	enum ctx_state prev_state = exception_enter();
>  	siginfo_t info;
>  
> +	CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
> +
>  	if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) !=
>  			NOTIFY_STOP) {
>  		conditional_sti(regs);
> @@ -376,6 +378,7 @@ dotraplinkage void do_bounds(struct pt_regs *regs, long error_code)
>  	siginfo_t *info;
>  
>  	prev_state = exception_enter();
> +	CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
>  	if (notify_die(DIE_TRAP, "bounds", regs, error_code,
>  			X86_TRAP_BR, SIGSEGV) == NOTIFY_STOP)
>  		goto exit;
> @@ -457,6 +460,7 @@ do_general_protection(struct pt_regs *regs, long error_code)
>  	enum ctx_state prev_state;
>  
>  	prev_state = exception_enter();
> +	CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
>  	conditional_sti(regs);
>  
>  	if (v8086_mode(regs)) {
> @@ -514,6 +518,7 @@ dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code)
>  		return;
>  
>  	prev_state = ist_enter(regs);
> +	CT_WARN_ON(ct_state() != CONTEXT_KERNEL);

Yeah, so any chance those assertions can be moved at the end of both
ist_enter() and exception_enter()?

Yeah, I read above that you're planning to rework it but it is cleaner
to have them at the end of the _enter() functions instead in all those
trap handlers, no...?

-- 
Regards/Gruss,
    Boris.

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