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Date: Wed, 11 Oct 2017 13:30:17 -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>,
	Kees Cook <keescook@...omium.org>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	Matthias Kaehlcke <mka@...omium.org>,
	Tom Lendacky <thomas.lendacky@....com>,
	Andy Lutomirski <luto@...nel.org>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	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>,
	Chris Wright <chrisw@...s-sol.org>,
	Alok Kataria <akataria@...are.com>,
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	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Lukas Wunner <lukas@...ner.de>,
	Masahiro Yamada <yamada.masahiro@...ionext.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Radim Krčmář <rkrcmar@...hat.com>,
	Joerg Roedel <joro@...tes.org>,
	Rik van Riel <riel@...hat.com>,
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	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
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	Kyle Huey <me@...ehuey.com>,
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	"H . J . Lu" <hjl.tools@...il.com>,
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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 v1 17/27] xen: Adapt assembly for PIE support

Change the assembly code to use the new _ASM_GET_PTR macro which get a
symbol reference while being PIE compatible. Adapt the relocation tool
to ignore 32-bit Xen code.

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/tools/relocs.c | 16 +++++++++++++++-
 arch/x86/xen/xen-head.S |  9 +++++----
 arch/x86/xen/xen-pvh.S  | 13 +++++++++----
 3 files changed, 29 insertions(+), 9 deletions(-)

diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
index 5d3eb2760198..bc032ad88b22 100644
--- a/arch/x86/tools/relocs.c
+++ b/arch/x86/tools/relocs.c
@@ -831,6 +831,16 @@ static int is_percpu_sym(ElfW(Sym) *sym, const char *symname)
 		strncmp(symname, "init_per_cpu_", 13);
 }
 
+/*
+ * Check if the 32-bit relocation is within the xenpvh 32-bit code.
+ * If so, ignores it.
+ */
+static int is_in_xenpvh_assembly(ElfW(Addr) offset)
+{
+	ElfW(Sym) *sym = sym_lookup("pvh_start_xen");
+	return sym && (offset >= sym->st_value) &&
+		(offset < (sym->st_value + sym->st_size));
+}
 
 static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
 		      const char *symname)
@@ -892,8 +902,12 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
 		 * the relocations are processed.
 		 * Make sure that the offset will fit.
 		 */
-		if (r_type != R_X86_64_64 && (int32_t)offset != (int64_t)offset)
+		if (r_type != R_X86_64_64 &&
+		    (int32_t)offset != (int64_t)offset) {
+			if (is_in_xenpvh_assembly(offset))
+				break;
 			die("Relocation offset doesn't fit in 32 bits\n");
+		}
 
 		if (r_type == R_X86_64_64)
 			add_reloc(&relocs64, offset);
diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index 124941d09b2b..e5b7b9566191 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -25,14 +25,15 @@ ENTRY(startup_xen)
 
 	/* Clear .bss */
 	xor %eax,%eax
-	mov $__bss_start, %_ASM_DI
-	mov $__bss_stop, %_ASM_CX
+	_ASM_GET_PTR(__bss_start, %_ASM_DI)
+	_ASM_GET_PTR(__bss_stop, %_ASM_CX)
 	sub %_ASM_DI, %_ASM_CX
 	shr $__ASM_SEL(2, 3), %_ASM_CX
 	rep __ASM_SIZE(stos)
 
-	mov %_ASM_SI, xen_start_info
-	mov $init_thread_union+THREAD_SIZE, %_ASM_SP
+	_ASM_GET_PTR(xen_start_info, %_ASM_AX)
+	mov %_ASM_SI, (%_ASM_AX)
+	_ASM_GET_PTR(init_thread_union+THREAD_SIZE, %_ASM_SP)
 
 	jmp xen_start_kernel
 END(startup_xen)
diff --git a/arch/x86/xen/xen-pvh.S b/arch/x86/xen/xen-pvh.S
index e1a5fbeae08d..43e234c7c2de 100644
--- a/arch/x86/xen/xen-pvh.S
+++ b/arch/x86/xen/xen-pvh.S
@@ -101,8 +101,8 @@ ENTRY(pvh_start_xen)
 	call xen_prepare_pvh
 
 	/* startup_64 expects boot_params in %rsi. */
-	mov $_pa(pvh_bootparams), %rsi
-	mov $_pa(startup_64), %rax
+	movabs $_pa(pvh_bootparams), %rsi
+	movabs $_pa(startup_64), %rax
 	jmp *%rax
 
 #else /* CONFIG_X86_64 */
@@ -137,10 +137,15 @@ END(pvh_start_xen)
 
 	.section ".init.data","aw"
 	.balign 8
+	/*
+	 * Use a quad for _pa(gdt_start) because PIE does not understand a
+	 * long is enough. The resulting value will still be in the lower long
+	 * part.
+	 */
 gdt:
 	.word gdt_end - gdt_start
-	.long _pa(gdt_start)
-	.word 0
+	.quad _pa(gdt_start)
+	.balign 8
 gdt_start:
 	.quad 0x0000000000000000            /* NULL descriptor */
 	.quad 0x0000000000000000            /* reserved */
-- 
2.15.0.rc0.271.g36b669edcc-goog

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