linux-kernel - [PATCH v11 08/11] x86/boot/64: Adapt assembly for PIE support

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Message-Id: <20200228000105.165012-9-thgarnie@chromium.org>
Date:   Thu, 27 Feb 2020 16:00:53 -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,
        Jiri Slaby <jslaby@...e.cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Cao jin <caoj.fnst@...fujitsu.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v11 08/11] x86/boot/64: Adapt assembly for PIE support

Change the assembly code to use absolute reference for transition
between address spaces and relative references when referencing global
variables in the same address space. Ensure the kernel built with PIE
references the correct addresses based on context.

Signed-off-by: Thomas Garnier <thgarnie@...omium.org>
Reviewed-by: Kees Cook <keescook@...omium.org>
---
 arch/x86/kernel/head_64.S | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 4bbc770af632..40a467f8e116 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -87,7 +87,8 @@ SYM_CODE_START_NOALIGN(startup_64)
 	popq	%rsi
 
 	/* Form the CR3 value being sure to include the CR3 modifier */
-	addq	$(early_top_pgt - __START_KERNEL_map), %rax
+	movabs  $(early_top_pgt - __START_KERNEL_map), %rcx
+	addq    %rcx, %rax
 	jmp 1f
 SYM_CODE_END(startup_64)
 
@@ -119,7 +120,8 @@ SYM_CODE_START(secondary_startup_64)
 	popq	%rsi
 
 	/* Form the CR3 value being sure to include the CR3 modifier */
-	addq	$(init_top_pgt - __START_KERNEL_map), %rax
+	movabs	$(init_top_pgt - __START_KERNEL_map), %rcx
+	addq    %rcx, %rax
 1:
 
 	/* Enable PAE mode, PGE and LA57 */
@@ -137,7 +139,7 @@ SYM_CODE_START(secondary_startup_64)
 	movq	%rax, %cr3
 
 	/* Ensure I am executing from virtual addresses */
-	movq	$1f, %rax
+	movabs  $1f, %rax
 	ANNOTATE_RETPOLINE_SAFE
 	jmp	*%rax
 1:
@@ -234,11 +236,12 @@ SYM_CODE_START(secondary_startup_64)
 	 *	REX.W + FF /5 JMP m16:64 Jump far, absolute indirect,
 	 *		address given in m16:64.
 	 */
-	pushq	$.Lafter_lret	# put return address on stack for unwinder
+	movabs  $.Lafter_lret, %rax
+	pushq	%rax		# put return address on stack for unwinder
 	xorl	%ebp, %ebp	# clear frame pointer
-	movq	initial_code(%rip), %rax
+	leaq	initial_code(%rip), %rax
 	pushq	$__KERNEL_CS	# set correct cs
-	pushq	%rax		# target address in negative space
+	pushq	(%rax)		# target address in negative space
 	lretq
 .Lafter_lret:
 SYM_CODE_END(secondary_startup_64)
-- 
2.25.1.481.gfbce0eb801-goog