linux-kernel - [PATCH v10 11/11] x86/alternatives: Adapt assembly for PIE support

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Message-Id: <20191205000957.112719-12-thgarnie@chromium.org>
Date:   Wed,  4 Dec 2019 16:09:48 -0800
From:   Thomas Garnier <thgarnie@...omium.org>
To:     kernel-hardening@...ts.openwall.com
Cc:     kristen@...ux.intel.com, keescook@...omium.org,
        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,
        Peter Zijlstra <peterz@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v10 11/11] x86/alternatives: Adapt assembly for PIE support

Change the assembly options to work with pointers instead of integers.
The generated code is the same PIE just ensures input is a pointer.

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/alternative.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index 13adca37c99a..43a148042656 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -243,7 +243,7 @@ static inline int alternatives_text_reserved(void *start, void *end)
 /* Like alternative_io, but for replacing a direct call with another one. */
 #define alternative_call(oldfunc, newfunc, feature, output, input...)	\
 	asm_inline volatile (ALTERNATIVE("call %P[old]", "call %P[new]", feature) \
-		: output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
+		: output : [old] "X" (oldfunc), [new] "X" (newfunc), ## input)
 
 /*
  * Like alternative_call, but there are two features and respective functions.
@@ -256,8 +256,8 @@ static inline int alternatives_text_reserved(void *start, void *end)
 	asm_inline volatile (ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1,\
 		"call %P[new2]", feature2)				      \
 		: output, ASM_CALL_CONSTRAINT				      \
-		: [old] "i" (oldfunc), [new1] "i" (newfunc1),		      \
-		  [new2] "i" (newfunc2), ## input)
+		: [old] "X" (oldfunc), [new1] "X" (newfunc1),		      \
+		  [new2] "X" (newfunc2), ## input)
 
 /*
  * use this macro(s) if you need more than one output parameter
-- 
2.24.0.393.g34dc348eaf-goog