linux-kernel - Re: [patch V2 08/17] x86/entry: Move syscall irq tracing to C code

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CALCETrWvnge064VUY3FQKens2Nx8BPNDhUZAXCvF6bD7VJy93A@mail.gmail.com>
Date:   Wed, 23 Oct 2019 14:35:20 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        kvm list <kvm@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>
Subject: Re: [patch V2 08/17] x86/entry: Move syscall irq tracing to C code

On Wed, Oct 23, 2019 at 2:30 PM Andy Lutomirski <luto@...nel.org> wrote:
>
> On Wed, Oct 23, 2019 at 5:31 AM Thomas Gleixner <tglx@...utronix.de> wrote:
> >
> > Interrupt state tracing can be safely done in C code. The few stack
> > operations in assembly do not need to be covered.
> >
> > Remove the now pointless indirection via .Lsyscall_32_done and jump to
> > swapgs_restore_regs_and_return_to_usermode directly.
>
> This doesn't look right.
>
> >  #define SYSCALL_EXIT_WORK_FLAGS                                \
> > @@ -279,6 +282,9 @@ static void syscall_slow_exit_work(struc
> >  {
> >         struct thread_info *ti;
> >
> > +       /* User to kernel transition disabled interrupts. */
> > +       trace_hardirqs_off();
> > +
>
> So you just traced IRQs off, but...
>
> >         enter_from_user_mode();
> >         local_irq_enable();
>
> Now they're on and traced on again?
>
> I also don't see how your patch handles the fastpath case.
>
> How about the attached patch instead?

Ignore the attached patch.  You have this in your
do_exit_to_usermode() later in the series.  But I'm still quite
confused by this patch.