linux-kernel - Re: [PATCH] x86/vdso: Fix vDSO build if a retpoline is emitted

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Date:   Thu, 16 Aug 2018 21:44:57 +0200
From:   David Woodhouse <dwmw2@...radead.org>
To:     Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Borislav Petkov <bp@...en8.de>,
        Matt Rickard <matt@...trans.com.au>,
        Jason Vas Dias <jason.vas.dias@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH] x86/vdso: Fix vDSO build if a retpoline is emitted



On Thu, 2018-08-16 at 12:41 -0700, Andy Lutomirski wrote:
> Currently, if the vDSO ends up containing an indirect branch or
> call, GCC will emit the "external thunk" style of retpoline, and it
> will fail to link.
> 
> Fix it by building the vDSO with inline retpoline thunks.
> 
> I haven't seen any reports of this triggering on an unpatched
> kernel.
> 
> Cc: Matt Rickard <matt@...trans.com.au>
> Cc: Jason Vas Dias <jason.vas.dias@...il.com>
> Cc: David Woodhouse <dwmw2@...radead.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Andi Kleen <ak@...ux.intel.com>
> Fixes: commit 76b043848fd2 ("x86/retpoline: Add initial retpoline support")
> Signed-off-by: Andy Lutomirski <luto@...nel.org>

Acked-by: David Woodhouse <dwmw@...zon.co.uk>

Thanks.
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