linux-kernel - [PATCH v6 07/27] x86/CPU: Adapt assembly for PIE support

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Date:   Thu, 31 Jan 2019 11:24:14 -0800
From:   Thomas Garnier <thgarnie@...omium.org>
To:     kernel-hardening@...ts.openwall.com
Cc:     kristen@...ux.intel.com, Thomas Garnier <thgarnie@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Garnier <thgarnie@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v6 07/27] x86/CPU: Adapt assembly for PIE support

Change the assembly code to use only relative references of symbols for the
kernel to be PIE compatible. Use the new _ASM_MOVABS macro instead of
the 'mov $symbol, %dst' construct.

Position Independent Executable (PIE) support will allow to extend the
KASLR randomization range below 0xffffffff80000000.

Signed-off-by: Thomas Garnier <thgarnie@...omium.org>
---
 arch/x86/include/asm/processor.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 33051436c864..ce9851bf6778 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -723,11 +723,13 @@ static inline void sync_core(void)
 		"pushfq\n\t"
 		"mov %%cs, %0\n\t"
 		"pushq %q0\n\t"
-		"pushq $1f\n\t"
+		"movabsq $1f, %q0\n\t"
+		"pushq %q0\n\t"
 		"iretq\n\t"
 		UNWIND_HINT_RESTORE
 		"1:"
-		: "=&r" (tmp), ASM_CALL_CONSTRAINT : : "cc", "memory");
+		: "=&r" (tmp), ASM_CALL_CONSTRAINT
+		: : "cc", "memory");
 #endif
 }
 
-- 
2.20.1.495.gaa96b0ce6b-goog