linux-kernel - [PATCH v5 06/27] x86/entry/64: Adapt assembly for PIE support

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Message-Id: <20180625224014.134829-7-thgarnie@google.com>
Date:   Mon, 25 Jun 2018 15:38:54 -0700
From:   Thomas Garnier <thgarnie@...gle.com>
To:     kernel-hardening@...ts.openwall.com
Cc:     Thomas Garnier <thgarnie@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v5 06/27] x86/entry/64: Adapt assembly for PIE support

Change the assembly code to use only relative references of symbols for the
kernel to be PIE compatible.

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

Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
---
 arch/x86/entry/entry_64.S            | 18 ++++++++++++------
 arch/x86/kernel/relocate_kernel_64.S |  8 +++-----
 2 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index c6f3677e6105..e738d8d0e308 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -191,7 +191,7 @@ ENTRY(entry_SYSCALL_64_trampoline)
 	 * spill RDI and restore it in a second-stage trampoline.
 	 */
 	pushq	%rdi
-	movq	$entry_SYSCALL_64_stage2, %rdi
+	movabsq	$entry_SYSCALL_64_stage2, %rdi
 	JMP_NOSPEC %rdi
 END(entry_SYSCALL_64_trampoline)
 
@@ -1277,7 +1277,8 @@ ENTRY(error_entry)
 	movl	%ecx, %eax			/* zero extend */
 	cmpq	%rax, RIP+8(%rsp)
 	je	.Lbstep_iret
-	cmpq	$.Lgs_change, RIP+8(%rsp)
+	leaq	.Lgs_change(%rip), %rcx
+	cmpq	%rcx, RIP+8(%rsp)
 	jne	.Lerror_entry_done
 
 	/*
@@ -1482,10 +1483,10 @@ ENTRY(nmi)
 	 * resume the outer NMI.
 	 */
 
-	movq	$repeat_nmi, %rdx
+	leaq	repeat_nmi(%rip), %rdx
 	cmpq	8(%rsp), %rdx
 	ja	1f
-	movq	$end_repeat_nmi, %rdx
+	leaq	end_repeat_nmi(%rip), %rdx
 	cmpq	8(%rsp), %rdx
 	ja	nested_nmi_out
 1:
@@ -1539,7 +1540,8 @@ nested_nmi:
 	pushq	%rdx
 	pushfq
 	pushq	$__KERNEL_CS
-	pushq	$repeat_nmi
+	leaq	repeat_nmi(%rip), %rdx
+	pushq	%rdx
 
 	/* Put stack back */
 	addq	$(6*8), %rsp
@@ -1578,7 +1580,11 @@ first_nmi:
 	addq	$8, (%rsp)	/* Fix up RSP */
 	pushfq			/* RFLAGS */
 	pushq	$__KERNEL_CS	/* CS */
-	pushq	$1f		/* RIP */
+	pushq	$0		/* Futur return address */
+	pushq	%rax		/* Save RAX */
+	leaq	1f(%rip), %rax	/* RIP */
+	movq    %rax, 8(%rsp)   /* Put 1f on return address */
+	popq	%rax		/* Restore RAX */
 	iretq			/* continues at repeat_nmi below */
 	UNWIND_HINT_IRET_REGS
 1:
diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index a7227dfe1a2b..0c0fc259a4e2 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -208,11 +208,9 @@ identity_mapped:
 	movq	%rax, %cr3
 	lea	PAGE_SIZE(%r8), %rsp
 	call	swap_pages
-	jmp	*virtual_mapped_addr(%rip)
-
-	/* Absolute value for PIE support */
-virtual_mapped_addr:
-	.quad virtual_mapped
+	movabsq $virtual_mapped, %rax
+	pushq	%rax
+	ret
 
 virtual_mapped:
 	movq	RSP(%r8), %rsp
-- 
2.18.0.rc2.346.g013aa6912e-goog