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Date:   Mon, 20 May 2019 20:12:55 -0700
From:   hpa@...or.com
To:     Thomas Garnier <thgarnie@...omium.org>,
        kernel-hardening@...ts.openwall.com
CC:     kristen@...ux.intel.com, Thomas Garnier <thgarnie@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Peter Zijlstra <peterz@...radead.org>,
        Nadav Amit <namit@...are.com>, Jann Horn <jannh@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 03/12] x86: Add macro to get symbol address for PIE support

On May 20, 2019 4:19:28 PM PDT, Thomas Garnier <thgarnie@...omium.org> wrote:
>From: Thomas Garnier <thgarnie@...gle.com>
>
>Add a new _ASM_MOVABS macro to fetch a symbol address. It will be used
>to replace "_ASM_MOV $<symbol>, %dst" code construct that are not
>compatible with PIE.
>
>Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
>---
> arch/x86/include/asm/asm.h | 1 +
> 1 file changed, 1 insertion(+)
>
>diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
>index 3ff577c0b102..3a686057e882 100644
>--- a/arch/x86/include/asm/asm.h
>+++ b/arch/x86/include/asm/asm.h
>@@ -30,6 +30,7 @@
> #define _ASM_ALIGN	__ASM_SEL(.balign 4, .balign 8)
> 
> #define _ASM_MOV	__ASM_SIZE(mov)
>+#define _ASM_MOVABS	__ASM_SEL(movl, movabsq)
> #define _ASM_INC	__ASM_SIZE(inc)
> #define _ASM_DEC	__ASM_SIZE(dec)
> #define _ASM_ADD	__ASM_SIZE(add)

This is just about *always* wrong on x86-86. We should be using leaq sym(%rip),%reg. If it isn't reachable by leaq, then it is a non-PIE symbol like percpu. You do have to keep those distinct!
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.

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