linux-kernel - Re: [PATCH v2 22/36] x86/entry: Add C code for fast system call entries

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: <CA+55aFx789UgJ-1FZK5JCjaXFnVqwTmuaTyv7y3wAdfP+h6Y9g@mail.gmail.com>
Date:	Tue, 6 Oct 2015 09:29:44 +0100
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Brian Gerst <brgerst@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH v2 22/36] x86/entry: Add C code for fast system call entries

On Tue, Oct 6, 2015 at 9:25 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
>> +       local_irq_enable();
>> +       if (get_user(*(u32 *)&regs->cx,
>> +                    (u32 __user __force *)(unsigned long)(u32)regs->sp)) {
> ...
>> +       local_irq_disable();
>
> this is expensive. Since we now do it in C code and can easily do
> this, why does the code not do this all with interrupts disabled,
> which is valid for user accesses but disables page faults, and then in
> the unlikely situation where that fails, we do it the slow and careful
> way?

Ok. I notice that then a later patch removes the local_irq_disable()
and calls do_syscall_32_irqs_on().

So I guess that "just run get_user with interrupts disabled"
optimization is pointless, because we'll just end up enabling
interrupts at some point anyway, and it can just be done before the
get_user().

So never mind.

            Linus
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/