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From: Ingo Molnar <mingo@kernel.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: "Andy Lutomirski" <luto@kernel.org>, "X86 ML" <x86@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Frédéric Weisbecker" <fweisbec@gmail.com>,
	"Rik van Riel" <riel@redhat.com>,
	"Oleg Nesterov" <oleg@redhat.com>,
	"Denys Vlasenko" <vda.linux@googlemail.com>,
	"Borislav Petkov" <bp@alien8.de>,
	"Kees Cook" <keescook@chromium.org>,
	"Brian Gerst" <brgerst@gmail.com>
Subject: Re: [RFC/INCOMPLETE 00/13] x86: Rewrite exit-to-userspace code
Date: Thu, 18 Jun 2015 18:24:22 +0200	[thread overview]
Message-ID: <20150618162422.GA6989@gmail.com> (raw)
In-Reply-To: <CALCETrVRF34yFtujk+gOUiiPG53bNu+WQH9MgvOa6pdUejb+Kw@mail.gmail.com>


* Andy Lutomirski <luto@amacapital.net> wrote:

> On Thu, Jun 18, 2015 at 3:11 AM, Ingo Molnar <mingo@kernel.org> wrote:
> >
> > * Andy Lutomirski <luto@amacapital.net> wrote:
> >
> >> > The only low level bits remaining in assembly will be low level hardware ABI
> >> > details: saving registers and restoring registers to the expected format - no
> >> > 'active' code whatsoever.
> >>
> >> I think this is true for syscalls.  Getting the weird special cases (IRET and 
> >> GS fault) for error_entry to work correctly in C could be tricky.
> >
> > Correct, and I double checked the IRET fault path yesterday (fixup_bad_iret), 
> > and it looks like a straightforward exception handler with limited control 
> > flow. It can stay in asm just fine, it seems mostly orthogonal to the rest.
> >
> > I didn't check the GS fault path, but that only affects 32-bit, as we use 
> > SWAPGS on 64-bit, right? In any case, that code too (32-bit RESTORE_REGS) 
> > belongs into the natural 'hardware ABI preparation code' that should stay in 
> > assembly. (Unless I missed some other code that might cause trouble.)
> 
> Look for "gs_change".  To change the gs selector, we do swapgs, then load gs, 
> then swapgs again.  If the gs load fails, then we trigger a special fixup.

Yes, but I don't see the connection to moving the syscall (and IRQ) entry code to 
.c: native_load_gs_index() is a separate API we call from regular kernel code, and 
it has a regular exception fixup entry plus a trap handler special case.

It's fine in entry_64.S, but it would be equally fine in inline asm() as well.

I think it's fine in entry_64.S as long as the error trap code (which refers to 
the change_gs RIP) lives there. But it could live in .c as well, as we can 
generate global symbols within inline asm() too.

Thanks,

	Ingo

      reply	other threads:[~2015-06-18 16:24 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-06-16 20:16 [RFC/INCOMPLETE 00/13] x86: Rewrite exit-to-userspace code Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 01/13] context_tracking: Add context_tracking_assert_state Andy Lutomirski
2015-06-17  9:41   ` Ingo Molnar
2015-06-17 14:15     ` Andy Lutomirski
2015-06-18  9:57       ` Ingo Molnar
2015-06-18 11:07         ` Andy Lutomirski
2015-06-18 15:52           ` Andy Lutomirski
2015-06-18 16:17             ` Ingo Molnar
2015-06-18 16:26               ` Frederic Weisbecker
2015-06-18 19:26                 ` Andy Lutomirski
2015-06-17 15:27     ` Paul E. McKenney
2015-06-18  9:59       ` Ingo Molnar
2015-06-18 22:54         ` Paul E. McKenney
2015-06-19  2:19           ` Paul E. McKenney
2015-06-30 11:04           ` Ingo Molnar
2015-06-30 16:16             ` Paul E. McKenney
2015-06-16 20:16 ` [RFC/INCOMPLETE 02/13] notifiers: Assert that RCU is watching in notify_die Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 03/13] x86: Move C entry and exit code to arch/x86/entry/common.c Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 04/13] x86/traps: Assert that we're in CONTEXT_KERNEL in exception entries Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 05/13] x86/entry: Add enter_from_user_mode and use it in syscalls Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 06/13] x86/entry: Add new, comprehensible entry and exit hooks Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 07/13] x86/entry/64: Really create an error-entry-from-usermode code path Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 08/13] x86/entry/64: Migrate 64-bit syscalls to new exit hooks Andy Lutomirski
2015-06-17 10:00   ` Ingo Molnar
2015-06-17 10:02     ` Ingo Molnar
2015-06-17 14:12       ` Andy Lutomirski
2015-06-18 10:17         ` Ingo Molnar
2015-06-18 10:19           ` Ingo Molnar
2015-06-16 20:16 ` [RFC/INCOMPLETE 09/13] x86/entry/compat: Migrate compat " Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 10/13] x86/asm/entry/64: Save all regs on interrupt entry Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 11/13] x86/asm/entry/64: Simplify irq stack pt_regs handling Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 12/13] x86/asm/entry/64: Migrate error and interrupt exit work to C Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 13/13] x86/entry: Remove SCHEDULE_USER and asm/context-tracking.h Andy Lutomirski
2015-06-17  9:48 ` [RFC/INCOMPLETE 00/13] x86: Rewrite exit-to-userspace code Ingo Molnar
2015-06-17 10:13   ` Richard Weinberger
2015-06-17 11:04     ` Ingo Molnar
2015-06-17 14:19     ` Andy Lutomirski
2015-06-17 15:16   ` Andy Lutomirski
2015-06-18 10:14     ` Ingo Molnar
2015-06-17 10:32 ` Ingo Molnar
2015-06-17 11:14   ` Ingo Molnar
2015-06-17 14:23   ` Andy Lutomirski
2015-06-18 10:11     ` Ingo Molnar
2015-06-18 11:06       ` Andy Lutomirski
2015-06-18 16:24         ` Ingo Molnar [this message]

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