From: David Woodhouse <dwmw2@infradead.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Borislav Petkov <bp@alien8.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 20:19:02 +0000 [thread overview]
Message-ID: <1515615542.22302.230.camel@infradead.org> (raw)
In-Reply-To: <20180110201532.5jnji6ypfl6slzvb@treble>
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On Wed, 2018-01-10 at 14:15 -0600, Josh Poimboeuf wrote:
> 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.
Strictly speaking, it's not about the ELF relocs. Those get processed
in advance, and the altinstructions already have them applied.
What Borislav had was a patch to process the actual branch
instructions, then frob their targets by {&altinstr - &oldinstr} to
make them work again... except it only worked by chance for targets
*within* the altinstr.
On the whole I think we're better off not touching that right now for
fear that it will introduce new bugs. But yes, it *should* be fixed....
just not this week please ;)
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next prev parent reply other threads:[~2018-01-10 20:19 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 [this message]
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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