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Date: Thu, 10 Aug 2017 10:26:07 -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>,
	Arnd Bergmann <arnd@...db.de>,
	Thomas Garnier <thgarnie@...gle.com>,
	Matthias Kaehlcke <mka@...omium.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Juergen Gross <jgross@...e.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Radim Krčmář <rkrcmar@...hat.com>,
	Joerg Roedel <joro@...tes.org>,
	Tom Lendacky <thomas.lendacky@....com>,
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	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
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	Len Brown <len.brown@...el.com>,
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	Lukas Wunner <lukas@...ner.de>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
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	Daniel Borkmann <daniel@...earbox.net>,
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	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Steven Rostedt <rostedt@...dmis.org>,
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	Waiman Long <longman@...hat.com>,
	Kyle Huey <me@...ehuey.com>,
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	Michal Hocko <mhocko@...e.com>,
	Matthew Wilcox <mawilcox@...rosoft.com>,
	"H . J . Lu" <hjl.tools@...il.com>,
	Paul Bolle <pebolle@...cali.nl>,
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	Daniel Micay <danielmicay@...il.com>
Cc: x86@...nel.org,
	linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	xen-devel@...ts.xenproject.org,
	kvm@...r.kernel.org,
	linux-pm@...r.kernel.org,
	linux-arch@...r.kernel.org,
	linux-sparse@...r.kernel.org,
	kernel-hardening@...ts.openwall.com
Subject: [RFC v2 15/23] x86/boot/64: Use _text in a global for PIE support

By default PIE generated code create only relative references so _text
points to the temporary virtual address. Instead use a global variable
so the relocation is done 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/head64.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 925b2928f377..e71f27a20576 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -45,8 +45,14 @@ static void __head *fixup_pointer(void *ptr, unsigned long physaddr)
 	return ptr - (void *)_text + (void *)physaddr;
 }
 
-unsigned long __head __startup_64(unsigned long physaddr,
-				  struct boot_params *bp)
+/*
+ * Use a global variable to properly calculate _text delta on PIE. By default
+ * a PIE binary do a RIP relative difference instead of the relocated address.
+ */
+unsigned long _text_offset = (unsigned long)(_text - __START_KERNEL_map);
+
+unsigned long __head notrace __startup_64(unsigned long physaddr,
+					  struct boot_params *bp)
 {
 	unsigned long load_delta, *p;
 	unsigned long pgtable_flags;
@@ -64,7 +70,7 @@ unsigned long __head __startup_64(unsigned long physaddr,
 	 * Compute the delta between the address I am compiled to run at
 	 * and the address I am actually running at.
 	 */
-	load_delta = physaddr - (unsigned long)(_text - __START_KERNEL_map);
+	load_delta = physaddr - _text_offset;
 
 	/* Is the address not 2M aligned? */
 	if (load_delta & ~PMD_PAGE_MASK)
-- 
2.14.0.434.g98096fd7a8-goog

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