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From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Borislav Petkov <bp@alien8.de>,
	David Woodhouse <dwmw2@infradead.org>,
	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 14:15:32 -0600	[thread overview]
Message-ID: <20180110201532.5jnji6ypfl6slzvb@treble> (raw)
In-Reply-To: <alpine.DEB.2.20.1801102053120.1919@nanos>

On Wed, Jan 10, 2018 at 08:55:40PM +0100, Thomas Gleixner wrote:
> On Wed, 10 Jan 2018, Linus Torvalds wrote:
> 
> > On Wed, Jan 10, 2018 at 3:28 AM, Borislav Petkov <bp@alien8.de> wrote:
> > >
> > > Make sure we scan all bytes before we decide to optimize the NOPs in
> > > there.
> > 
> > Can we also add compile-time checking (presumably in objtool, but who
> > knows) that there are no relocations in the alternative section?
> 
> Cc'ing the overlor^Haded objtool wizard
> 
> > Because that was the other "oops, this really doesn't work with
> > altinstructions" issue, wasn't it?

I think .altinstruction relocations *do* work if they're for the first
instruction, and it's a jump or a call.  There's some alternatives code
which adjusts the jump/call offset in that case, and there are some
users of alternatives who rely on that.

I think Boris had a patch floating around to add an instruction decoder
to alternatives, so you can do a call/jmp anywhere.

-- 
Josh

  reply	other threads:[~2018-01-10 20:15 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 [this message]
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
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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