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From: David Woodhouse <dwmw2@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>,
	Borislav Petkov <bp@alien8.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andi Kleen <andi@firstfloor.org>,
	the arch/x86 maintainers <x86@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Paul Turner <pjt@google.com>, Andrew Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Greg Kroah-Hartman <gregkh@linux-foundation.org>,
	Dave Hansen <dave.hansen@intel.com>,
	Jiri Kosina <jikos@kernel.org>, Andi Kleen <ak@linux.intel.com>
Subject: Re: [PATCH] x86/alternatives: Fix optimize_nops() checking
Date: Wed, 10 Jan 2018 21:08:57 +0000	[thread overview]
Message-ID: <1515618537.22302.253.camel@infradead.org> (raw)
In-Reply-To: <CA+55aFykL6+9kJjP2J-y3D7h7s3KhASVJ_cULa12zk5o37=OsA@mail.gmail.com>

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On Wed, 2018-01-10 at 13:05 -0800, Linus Torvalds wrote:
> On Wed, Jan 10, 2018 at 12:55 PM, Borislav Petkov <bp@alien8.de>
> wrote:
> >
> > Ok, so the problem was: how to fixup jumps which are not the first
> > instruction which is being replaced but a following one in the
> > instruction bytes with which we replace.
> 
> What jumps do you have that need to be fixed up?
> 
> I really think we should avoid having things like that.
> 
> Any jumps *within* the alternatives should have been handled by the
> assembler already.
> 
> And jumps between the alternatives and other places? Why do they
> exist?

There are a few of the form 'call *somefunc'.

The existing code handles them not by virtue of the relocs, as I said,
but by a simple delta of the old and new location of the instruction.

But it only does so for the *first* instruction of the altinstr, if it
happens to be a (4-byte?) branch.

Right now for retpoline I am just studiously avoiding doing anything
that the alternatives mechanism isn't going to get right, or might
change in future. I think ;)


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  reply	other threads:[~2018-01-10 21:09 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-10  0:31 [PATCH] x86/retpoline: Fix NOSPEC_JMP for tip Andi Kleen
2018-01-10  0:39 ` Thomas Gleixner
2018-01-10  0:39 ` Linus Torvalds
2018-01-10  0:40   ` Thomas Gleixner
2018-01-10  0:45     ` Tom Lendacky
2018-01-10  0:50       ` Thomas Gleixner
2018-01-10  1:30       ` Andi Kleen
2018-01-10  1:36         ` Andi Kleen
2018-01-10  1:50           ` Thomas Gleixner
2018-01-10  1:57             ` Andi Kleen
2018-01-10  9:05         ` David Woodhouse
2018-01-10  0:51   ` Andi Kleen
2018-01-10  1:05     ` Thomas Gleixner
2018-01-10  7:15   ` David Woodhouse
2018-01-10 10:05     ` David Woodhouse
2018-01-10 11:28       ` [PATCH] x86/alternatives: Fix optimize_nops() checking Borislav Petkov
2018-01-10 11:36         ` David Woodhouse
2018-01-10 11:45           ` Borislav Petkov
2018-01-10 11:49             ` David Woodhouse
2018-01-10 11:57               ` Borislav Petkov
2018-01-10 11:58                 ` David Woodhouse
2018-01-10 17:33         ` [tip:x86/pti] " tip-bot for Borislav Petkov
2018-01-10 18:12         ` tip-bot for Borislav Petkov
2018-01-10 18:39         ` tip-bot for Borislav Petkov
2018-01-10 19:38         ` [PATCH] " Linus Torvalds
2018-01-10 19:55           ` Thomas Gleixner
2018-01-10 20:15             ` Josh Poimboeuf
2018-01-10 20:19               ` David Woodhouse
2018-01-10 20:26               ` Linus Torvalds
2018-01-10 20:33                 ` Peter Zijlstra
2018-01-10 20:36                   ` David Woodhouse
2018-01-10 20:49                   ` Linus Torvalds
2018-01-10 20:55                 ` Borislav Petkov
2018-01-10 21:05                   ` Linus Torvalds
2018-01-10 21:08                     ` David Woodhouse [this message]
2018-01-10 21:11                       ` Linus Torvalds
2018-01-10 21:16                         ` Josh Poimboeuf
2018-01-10 21:17                         ` Linus Torvalds
2018-01-10 21:27                           ` Josh Poimboeuf
2018-01-10 21:10                     ` Borislav Petkov
2018-01-10 20:55                 ` Josh Poimboeuf
2018-01-10 20:05           ` Borislav Petkov
2018-01-10 20:20             ` Linus Torvalds
2018-01-10 20:50               ` Borislav Petkov

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