From: "H. Peter Anvin" <hpa@zytor.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>,
Denys Vlasenko <dvlasenk@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Steven Rostedt <rostedt@goodmis.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>,
X86 ML <x86@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/4] x86: entry.S: tidy up several suboptimal insns
Date: Wed, 25 Feb 2015 01:27:25 -0800 [thread overview]
Message-ID: <54ED957D.8000709@zytor.com> (raw)
In-Reply-To: <20150225092043.GB16165@gmail.com>
On 02/25/2015 01:20 AM, Ingo Molnar wrote:
>
> I think the fundamental fragility is that we allow the high
> 32 bits to be nonzero.
>
> So could we just zap the high 32 bits of RAX early in the
> entry code, and then from that point on we could both use
> 32-bit ops and won't have to remember the possibility
> either?
>
We do that, but people keep "optimizing" the zero extend away. We have
had this cause a wide-open security hole twice already. So the extra
REX prefix is a cheap cost to avoid this happen again.
-hpa
next prev parent reply other threads:[~2015-02-25 9:27 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-24 18:51 [PATCH 1/4] x86: entry.S: tidy up several suboptimal insns Denys Vlasenko
2015-02-24 18:51 ` [PATCH 2/4] x86: get rid of KERNEL_STACK_OFFSET Denys Vlasenko
2015-02-24 19:30 ` Steven Rostedt
2015-02-24 20:02 ` Denys Vlasenko
2015-02-24 22:37 ` Andy Lutomirski
2015-02-25 9:45 ` Ingo Molnar
2015-02-25 16:14 ` Andy Lutomirski
2015-02-26 11:42 ` Ingo Molnar
2015-02-26 15:21 ` Andy Lutomirski
2015-02-26 15:29 ` Andy Lutomirski
2015-02-25 8:53 ` Ingo Molnar
2015-02-25 12:48 ` Denys Vlasenko
2015-02-25 13:25 ` Denys Vlasenko
2015-02-25 13:53 ` Ingo Molnar
2015-02-24 18:51 ` [PATCH 3/4] x86: save r11 into pt_regs->eflags on SYSCALL64 fastpath Denys Vlasenko
2015-02-24 22:44 ` Andy Lutomirski
2015-02-24 18:51 ` [PATCH 4/4] x86: save user %rsp in pt_regs->sp Denys Vlasenko
2015-02-24 22:55 ` Andy Lutomirski
2015-02-24 19:58 ` [PATCH 1/4] x86: entry.S: tidy up several suboptimal insns Borislav Petkov
2015-02-24 20:13 ` Denys Vlasenko
2015-02-24 20:36 ` Borislav Petkov
2015-02-24 22:51 ` H. Peter Anvin
2015-02-24 22:25 ` Andy Lutomirski
2015-02-24 22:52 ` H. Peter Anvin
2015-02-24 22:56 ` Andy Lutomirski
2015-02-24 23:01 ` H. Peter Anvin
2015-02-24 23:03 ` Andy Lutomirski
2015-02-24 23:26 ` Denys Vlasenko
2015-02-25 9:20 ` Ingo Molnar
2015-02-25 9:27 ` H. Peter Anvin [this message]
2015-02-25 9:39 ` Ingo Molnar
2015-02-25 14:43 ` Steven Rostedt
2015-02-25 15:40 ` Denys Vlasenko
2015-02-25 16:01 ` Steven Rostedt
2015-02-25 16:06 ` Borislav Petkov
2015-02-26 11:47 ` Ingo Molnar
2015-02-26 12:47 ` Steven Rostedt
2015-02-26 12:50 ` Steven Rostedt
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