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Date: Tue, 13 Mar 2018 13:59:28 -0700
From: Thomas Garnier <thgarnie@...gle.com>
To: Herbert Xu <herbert@...dor.apana.org.au>,
	"David S . Miller" <davem@...emloft.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Kate Stewart <kstewart@...uxfoundation.org>,
	Thomas Garnier <thgarnie@...gle.com>,
	Arnd Bergmann <arnd@...db.de>,
	Philippe Ombredanne <pombredanne@...b.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	Matthias Kaehlcke <mka@...omium.org>,
	Kees Cook <keescook@...omium.org>,
	Tom Lendacky <thomas.lendacky@....com>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>,
	Dominik Brodowski <linux@...inikbrodowski.net>,
	Borislav Petkov <bp@...en8.de>,
	Borislav Petkov <bp@...e.de>,
	"Rafael J . Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>,
	Pavel Machek <pavel@....cz>,
	Juergen Gross <jgross@...e.com>,
	Alok Kataria <akataria@...are.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Tejun Heo <tj@...nel.org>,
	Christoph Lameter <cl@...ux.com>,
	Dennis Zhou <dennisszhou@...il.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	David Woodhouse <dwmw@...zon.co.uk>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	"Luis R . Rodriguez" <mcgrof@...nel.org>,
	Christopher Li <sparse@...isli.org>,
	Jason Baron <jbaron@...mai.com>,
	Ashish Kalra <ashish@...estacks.com>,
	Kyle McMartin <kyle@...hat.com>,
	Dou Liyang <douly.fnst@...fujitsu.com>,
	Lukas Wunner <lukas@...ner.de>,
	Petr Mladek <pmladek@...e.com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Masahiro Yamada <yamada.masahiro@...ionext.com>,
	Ingo Molnar <mingo@...nel.org>,
	Nicholas Piggin <npiggin@...il.com>,
	Cao jin <caoj.fnst@...fujitsu.com>,
	"H . J . Lu" <hjl.tools@...il.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Radim Krčmář <rkrcmar@...hat.com>,
	Joerg Roedel <joro@...tes.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>,
	Jia Zhang <qianyue.zj@...baba-inc.com>,
	Jiri Slaby <jslaby@...e.cz>,
	Kyle Huey <me@...ehuey.com>,
	Jonathan Corbet <corbet@....net>,
	Matthew Wilcox <mawilcox@...rosoft.com>,
	Michal Hocko <mhocko@...e.com>,
	Rob Landley <rob@...dley.net>,
	Baoquan He <bhe@...hat.com>,
	Daniel Micay <danielmicay@...il.com>,
	Jan H . Schönherr <jschoenh@...zon.de>
Cc: x86@...nel.org,
	linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	xen-devel@...ts.xenproject.org,
	linux-arch@...r.kernel.org,
	linux-sparse@...r.kernel.org,
	kvm@...r.kernel.org,
	linux-doc@...r.kernel.org,
	kernel-hardening@...ts.openwall.com
Subject: [PATCH v2 10/27] x86/boot/64: Adapt assembly for PIE support

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

Early at boot, the kernel is mapped at a temporary address while preparing
the page table. To know the changes needed for the page table with KASLR,
the boot code calculate the difference between the expected address of the
kernel and the one chosen by KASLR. It does not work with PIE because all
symbols in code are relatives. Instead of getting the future relocated
virtual address, you will get the current temporary mapping. The solution
is using global variables that will be relocated as expected.

Position Independent Executable (PIE) support will allow to extended the
KASLR randomization range below the -2G memory limit.

Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
---
 arch/x86/kernel/head_64.S | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 48385c1074a5..48652f3ec46a 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -89,8 +89,9 @@ startup_64:
 	popq	%rsi
 
 	/* Form the CR3 value being sure to include the CR3 modifier */
-	addq	$(early_top_pgt - __START_KERNEL_map), %rax
+	addq    _early_top_pgt_offset(%rip), %rax
 	jmp 1f
+
 ENTRY(secondary_startup_64)
 	UNWIND_HINT_EMPTY
 	/*
@@ -119,7 +120,7 @@ ENTRY(secondary_startup_64)
 	popq	%rsi
 
 	/* Form the CR3 value being sure to include the CR3 modifier */
-	addq	$(init_top_pgt - __START_KERNEL_map), %rax
+	addq    _init_top_offset(%rip), %rax
 1:
 
 	/* Enable PAE mode, PGE and LA57 */
@@ -137,7 +138,7 @@ ENTRY(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 +235,12 @@ ENTRY(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
+	leaq	.Lafter_lret(%rip), %rax
+	pushq	%rax		# put return address on stack for unwinder
 	xorq	%rbp, %rbp	# 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:
 END(secondary_startup_64)
@@ -342,6 +344,18 @@ END(early_idt_handler_common)
 GLOBAL(early_recursion_flag)
 	.long 0
 
+	/*
+	 * Position Independent Code takes only relative references in code
+	 * meaning a global variable address is relative to RIP and not its
+	 * future virtual address. Global variables can be used instead as they
+	 * are still relocated on the expected kernel mapping address.
+	 */
+	.align 8
+_early_top_pgt_offset:
+	.quad early_top_pgt - __START_KERNEL_map
+_init_top_offset:
+	.quad init_top_pgt - __START_KERNEL_map
+
 #define NEXT_PAGE(name) \
 	.balign	PAGE_SIZE; \
 GLOBAL(name)
-- 
2.16.2.660.g709887971b-goog

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