linux-kernel - [PATCH v4 08/27] x86/CPU: Adapt assembly for PIE support

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Message-Id: <20180529221625.33541-9-thgarnie@google.com>
Date:   Tue, 29 May 2018 15:15:09 -0700
From:   Thomas Garnier <thgarnie@...gle.com>
To:     kernel-hardening@...ts.openwall.com
Cc:     Thomas Garnier <thgarnie@...gle.com>,
        "Skip Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Skip Vitaly Kuznetsov <vkuznets@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Borislav Petkov <bp@...e.de>,
        Andy Lutomirski <luto@...nel.org>, linux-kernel@...r.kernel.org
Subject: [PATCH v4 08/27] 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 0xffffffff80000000.

Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
---
 arch/x86/include/asm/processor.h | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index e28add6b791f..7ae9fb91f7b5 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -50,7 +50,7 @@ static inline void *current_text_addr(void)
 {
 	void *pc;
 
-	asm volatile("mov $1f, %0; 1:":"=r" (pc));
+	asm volatile(_ASM_MOVABS " $1f, %0; 1:":"=r" (pc));
 
 	return pc;
 }
@@ -711,6 +711,7 @@ static inline void sync_core(void)
 		: ASM_CALL_CONSTRAINT : : "memory");
 #else
 	unsigned int tmp;
+	unsigned long tmp2;
 
 	asm volatile (
 		UNWIND_HINT_SAVE
@@ -721,11 +722,13 @@ static inline void sync_core(void)
 		"pushfq\n\t"
 		"mov %%cs, %0\n\t"
 		"pushq %q0\n\t"
-		"pushq $1f\n\t"
+		"leaq 1f(%%rip), %1\n\t"
+		"pushq %1\n\t"
 		"iretq\n\t"
 		UNWIND_HINT_RESTORE
 		"1:"
-		: "=&r" (tmp), ASM_CALL_CONSTRAINT : : "cc", "memory");
+		: "=&r" (tmp), "=&r" (tmp2), ASM_CALL_CONSTRAINT
+		: : "cc", "memory");
 #endif
 }
 
-- 
2.17.0.921.gf22659ad46-goog