From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Josh Poimboeuf <jpoimboe@redhat.com>
Date: Mon, 18 Sep 2017 21:43:37 -0500
Subject: [PATCH] x86/head: Add unwind hint annotations
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CVE-2017-5754

Jiri Slaby reported an ORC issue when unwinding from an idle task.  The
stack was:

    ffffffff811083c2 do_idle+0x142/0x1e0
    ffffffff8110861d cpu_startup_entry+0x5d/0x60
    ffffffff82715f58 start_kernel+0x3ff/0x407
    ffffffff827153e8 x86_64_start_kernel+0x14e/0x15d
    ffffffff810001bf secondary_startup_64+0x9f/0xa0

The ORC unwinder errored out at secondary_startup_64 because the head
code isn't annotated yet so there wasn't a corresponding ORC entry.

Fix that and any other head-related unwinding issues by adding unwind
hints to the head code.

Reported-by: Jiri Slaby <jslaby@suse.cz>
Tested-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/78ef000a2f68f545d6eef44ee912edceaad82ccf.1505764066.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 2704fbb672d0d9a19414907fda7949283dcef6a1)
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
(cherry picked from commit b63a868e404e64172afefea553c6a40963a151db)
Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
---
 arch/x86/kernel/Makefile  |  1 -
 arch/x86/kernel/head_64.S | 14 ++++++++++++--
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 287eac7d207f..e2315aecc441 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -26,7 +26,6 @@ KASAN_SANITIZE_dumpstack.o				:= n
 KASAN_SANITIZE_dumpstack_$(BITS).o			:= n
 KASAN_SANITIZE_stacktrace.o := n
 
-OBJECT_FILES_NON_STANDARD_head_$(BITS).o		:= y
 OBJECT_FILES_NON_STANDARD_relocate_kernel_$(BITS).o	:= y
 OBJECT_FILES_NON_STANDARD_ftrace_$(BITS).o		:= y
 OBJECT_FILES_NON_STANDARD_test_nx.o			:= y
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 45b18b1a6417..d081bc7a027d 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -49,6 +49,7 @@ L3_START_KERNEL = pud_index(__START_KERNEL_map)
 	.code64
 	.globl startup_64
 startup_64:
+	UNWIND_HINT_EMPTY
 	/*
 	 * At this point the CPU runs in 64bit mode CS.L = 1 CS.D = 0,
 	 * and someone has loaded an identity mapped page table
@@ -81,6 +82,7 @@ startup_64:
 	movq	$(early_top_pgt - __START_KERNEL_map), %rax
 	jmp 1f
 ENTRY(secondary_startup_64)
+	UNWIND_HINT_EMPTY
 	/*
 	 * At this point the CPU runs in 64bit mode CS.L = 1 CS.D = 0,
 	 * and someone has loaded a mapped page table.
@@ -116,6 +118,7 @@ ENTRY(secondary_startup_64)
 	movq	$1f, %rax
 	jmp	*%rax
 1:
+	UNWIND_HINT_EMPTY
 
 	/* Check if nx is implemented */
 	movl	$0x80000001, %eax
@@ -230,6 +233,7 @@ END(secondary_startup_64)
  */
 ENTRY(start_cpu0)
 	movq	initial_stack(%rip), %rsp
+	UNWIND_HINT_EMPTY
 	jmp	.Ljump_to_C_code
 ENDPROC(start_cpu0)
 #endif
@@ -254,13 +258,18 @@ ENTRY(early_idt_handler_array)
 	i = 0
 	.rept NUM_EXCEPTION_VECTORS
 	.ifeq (EXCEPTION_ERRCODE_MASK >> i) & 1
-	pushq $0		# Dummy error code, to make stack frame uniform
+		UNWIND_HINT_IRET_REGS
+		pushq $0	# Dummy error code, to make stack frame uniform
+	.else
+		UNWIND_HINT_IRET_REGS offset=8
 	.endif
 	pushq $i		# 72(%rsp) Vector number
 	jmp early_idt_handler_common
+	UNWIND_HINT_IRET_REGS
 	i = i + 1
 	.fill early_idt_handler_array + i*EARLY_IDT_HANDLER_SIZE - ., 1, 0xcc
 	.endr
+	UNWIND_HINT_IRET_REGS offset=16
 END(early_idt_handler_array)
 
 early_idt_handler_common:
@@ -289,6 +298,7 @@ early_idt_handler_common:
 	pushq %r13				/* pt_regs->r13 */
 	pushq %r14				/* pt_regs->r14 */
 	pushq %r15				/* pt_regs->r15 */
+	UNWIND_HINT_REGS
 
 	cmpq $14,%rsi		/* Page fault? */
 	jnz 10f
@@ -411,7 +421,7 @@ ENTRY(phys_base)
 EXPORT_SYMBOL(phys_base)
 
 #include "../../x86/xen/xen-head.S"
-	
+
 	__PAGE_ALIGNED_BSS
 NEXT_PAGE(empty_zero_page)
 	.skip PAGE_SIZE
-- 
2.14.2

