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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
	Denys Vlasenko <dvlasenk@redhat.com>,
	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, 9 Mar 2015 10:59:35 -0700	[thread overview]
Message-ID: <CA+55aFz2HOnPg9i4WSeL4rQgSJDUXbiWjbqnODib=vyWrPuJEg@mail.gmail.com> (raw)
In-Reply-To: <CALCETrV8BhaL9MUv9ZroyWwrBKdDXL+ZwY3dELO80N3bcsxi5A@mail.gmail.com>

On Mon, Mar 9, 2015 at 10:45 AM, Andy Lutomirski <luto@amacapital.net> wrote:
>
> If sp0 is set to the very top of the stack, then an NMI immediately
> after sysenter will have OLDSS off the top of the stack, and reading
> it can crash.  This is why 32-bit kernels have a (buggy!) 8 byte
> offset in sp0.

So I think that for sysenter, we *should* have that 8-byte buffer.

Not in general for sp0, but for MSR_IA32_SYSENTER_ESP (which is sp1, afaik).

Just make the rule be that you can never ever have a kernel stack
frame that doesn't contain room for ss/sp at the top.

We have various code that looks at and touches "pt_regs" anyway, and
accesses things out for debugging/oopsing/tracing etc. Let's not make
the rule be that you cannot look at regs->ss without checking various
random other fields first.

                         Linus

  reply	other threads:[~2015-03-09 17:59 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-09 14:05 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
2015-03-09 17:45     ` Andy Lutomirski
2015-03-09 17:59       ` Linus Torvalds [this message]
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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