Re: [PATCH v4 07/17] x86/traps: Assert that we're in CONTEXT_KERNEL in exception entries

Andy Lutomirski
2015-06-30T17:08:30Z

On Tue, Jun 30, 2015 at 10:01 AM, Borislav Petkov <bp@alien8.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@kernel.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