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Date: Mon, 29 Jan 2018 18:44:03 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: David Woodhouse <dwmw2@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Josh Poimboeuf <jpoimboe@redhat.com>, linux-kernel@vger.kernel.org,
	Dave Hansen <dave.hansen@intel.com>,
	Ashok Raj <ashok.raj@intel.com>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Greg KH <gregkh@linuxfoundation.org>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Andi Kleen <ak@linux.intel.com>,
	Arjan Van De Ven <arjan.van.de.ven@intel.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Jun Nakajima <jun.nakajima@intel.com>,
	Asit Mallick <asit.k.mallick@intel.com>,
	Jason Baron <jbaron@akamai.com>
Subject: Re: [PATCH 04/24] x86,nospec: Annotate indirect calls/jumps
Message-ID: <20180129174403.GH2228@hirez.programming.kicks-ass.net>
References: <20180123152539.374360046@infradead.org>
 <20180123152638.217996936@infradead.org>
 <1516961987.30244.178.camel@infradead.org>
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On Fri, Jan 26, 2018 at 10:19:47AM +0000, David Woodhouse wrote:
> On Tue, 2018-01-23 at 16:25 +0100, Peter Zijlstra wrote:
> > Annotate the indirect calls/jumps in the CALL_NOSPEC/JUMP_NOSPEC
> > alternatives.
> > 
> > 
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> 
> Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
> 
> However...
> 
> 
> >  /*
> > + * This should be used immediately before an indirect jump/call. It tells
> > + * objtool the subsequent indirect jump/call is vouched safe for retpoline
> > + * builds.
> > + */
> > +.macro ANNOTATE_RETPOLINE_SAFE
> > +	.Lannotate_\@:
> > +	.pushsection .discard.retpoline_safe
> > +	_ASM_PTR .Lannotate_\@
> > +	.popsection
> > +.endm
> 
> Didn't I just see one of those in patch 3? So this makes two...
> 
> 
> 
> > @@ -143,6 +155,12 @@
> >  	".long 999b - .\n\t"					\
> >  	".popsection\n\t"
> >  
> > +#define ANNOTATE_RETPOLINE_SAFE					\
> > +	"999:\n\t"						\
> > +	".pushsection .discard.retpoline_safe\n\t"		\
> > +	_ASM_PTR " 999b\n\t"					\
> > +	".popsection\n\t"
> > +
> >  #if defined(CONFIG_X86_64) && defined(RETPOLINE)
> 
> ... three.
> 
> Now, I did briefly toy with the idea of using a .macro from both
> __ASSEMBLY__ and inline asm, making the latter work by means of 
> asm(".include \"asm/nospec-branch.h\");
> 
> In the end I just ended up with the __FILL_RETURN_BUFFER CPP macro
> which is used from both by other tricks.
> 
> Can we look at doing something like that, please?


I'll try. The paravirt one might be tricky, I always end in header-hell
with that thing.