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

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Date:	Tue, 30 Jun 2015 10:08:00 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.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>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v4 07/17] x86/traps: Assert that we're in CONTEXT_KERNEL
 in exception entries

On Tue, Jun 30, 2015 at 10:01 AM, Borislav Petkov <bp@...en8.de> wrote:
> 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...?
>

I would agree, except that I remove the exception_enter calls later in
the series, so that wouldn't work.  Maybe we should move them into
common code outside the specific exception handlers (idtentry?) when
the dust settles.

--Andy
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