From: "H. Peter Anvin" <hpa@zytor.com>
To: Linus Torvalds <torvalds@linux-foundation.org>,
Denys Vlasenko <dvlasenk@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>,
Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>,
Oleg Nesterov <oleg@redhat.com>,
Frederic Weisbecker <fweisbec@gmail.com>,
Alexei Starovoitov <ast@plumgrid.com>,
Will Drewry <wad@chromium.org>, Kees Cook <keescook@chromium.org>,
the arch/x86 maintainers <x86@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86: entry_32.S: change ESPFIX test to not touch PT_OLDSS(%esp)
Date: Mon, 09 Mar 2015 10:42:40 -0700 [thread overview]
Message-ID: <54FDDB90.9010706@zytor.com> (raw)
In-Reply-To: <CA+55aFzck8nuV06AZhhFXgUQEsujZCtufw0jY4iswJUggh6ruA@mail.gmail.com>
On 03/09/2015 09:08 AM, Linus Torvalds wrote:
>
> Sure, the btl is easier to explain in the source code, but instead of this:
>
>> + btl $X86_EFLAGS_VM_BIT,PT_EFLAGS(%esp)
>
> you'd have to add a comment, like
>
> testb $2, PT_EFLAGS+2(%esp) # X86_EFLAGS_VM_BIT
>
> or something.
>
Maybe:
testb $(X86_EFLAGS_VM-16), PT_EFLAGS+2(%esp)
> Or just at least *partially* do what we used to do, and make it all be
>
> movb PT_EFLAGS+2(%esp),%al
> andb $2,%al
> orb PT_CS(%esp),%al
> testb $3,%al
> je restore_nocheck
> testb $SEGMENT_TI_MASK,PT_OLDSS(%esp)
> jne ldt_ss
>
> which still avoids looking at SS unless needed, and is smaller and
> faster than the btl, afaik.
The question is if avoiding looking at a field on the stack matters at all.
-hpa
next prev parent reply other threads:[~2015-03-09 17:43 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-09 14:05 [PATCH] x86: entry_32.S: change ESPFIX test to not touch PT_OLDSS(%esp) Denys Vlasenko
2015-03-09 14:18 ` Andy Lutomirski
2015-03-09 15:00 ` Denys Vlasenko
2015-03-09 15:09 ` Andy Lutomirski
2015-03-09 19:31 ` Denys Vlasenko
2015-03-09 15:13 ` Ingo Molnar
2015-03-09 15:18 ` Andy Lutomirski
2015-03-09 15:47 ` Steven Rostedt
2015-03-09 15:54 ` Ingo Molnar
2015-03-09 16:08 ` Linus Torvalds
2015-03-09 16:28 ` Denys Vlasenko
2015-03-09 16:44 ` Linus Torvalds
2015-03-09 17:44 ` H. Peter Anvin
2015-03-09 19:13 ` Andy Lutomirski
2015-03-09 19:26 ` H. Peter Anvin
2015-03-09 19:51 ` Andy Lutomirski
2015-03-09 17:42 ` H. Peter Anvin [this message]
2015-03-09 17:45 ` Andy Lutomirski
2015-03-09 17:59 ` Linus Torvalds
2015-03-09 18:04 ` Andy Lutomirski
2015-03-09 18:16 ` Linus Torvalds
2015-03-09 18:32 ` Denys Vlasenko
2015-03-09 18:36 ` Andy Lutomirski
2015-03-10 6:25 ` Ingo Molnar
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