pve-edge-kernel/patches/kernel/0019-x86-entry-64-Initialize-the-top-of-the-IRQ-stack-bef.patch

From 63463bcffe420067411ad3d4d01b79c872fffc3a Mon Sep 17 00:00:00 2001
From: Andy Lutomirski <[email protected]>
Date: Tue, 11 Jul 2017 10:33:39 -0500
Subject: [PATCH 019/242] x86/entry/64: Initialize the top of the IRQ stack
 before switching stacks
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CVE-2017-5754

The OOPS unwinder wants the word at the top of the IRQ stack to
point back to the previous stack at all times when the IRQ stack
is in use.  There's currently a one-instruction window in ENTER_IRQ_STACK
during which this isn't the case.  Fix it by writing the old RSP to the
top of the IRQ stack before jumping.

This currently writes the pointer to the stack twice, which is a bit
ugly.  We could get rid of this by replacing irq_stack_ptr with
irq_stack_ptr_minus_eight (better name welcome).  OTOH, there may be
all kinds of odd microarchitectural considerations in play that
affect performance by a few cycles here.

Reported-by: Mike Galbraith <[email protected]>
Reported-by: Josh Poimboeuf <[email protected]>
Signed-off-by: Andy Lutomirski <[email protected]>
Signed-off-by: Josh Poimboeuf <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Jiri Slaby <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/aae7e79e49914808440ad5310ace138ced2179ca.1499786555.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <[email protected]>
(cherry picked from commit 2995590964da93e1fd9a91550f9c9d9fab28f160)
Signed-off-by: Andy Whitcroft <[email protected]>
Signed-off-by: Kleber Sacilotto de Souza <[email protected]>
(cherry picked from commit a753ff654dfd07a7f8d6f39a27126589eac7e55f)
Signed-off-by: Fabian Grünbichler <[email protected]>
---
 arch/x86/entry/entry_64.S | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 07b4056af8a8..184b70712545 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -469,6 +469,7 @@ END(irq_entries_start)
 	DEBUG_ENTRY_ASSERT_IRQS_OFF
 	movq	%rsp, \old_rsp
 	incl	PER_CPU_VAR(irq_count)
+	jnz	.Lirq_stack_push_old_rsp_\@
 
 	/*
 	 * Right now, if we just incremented irq_count to zero, we've
@@ -478,9 +479,30 @@ END(irq_entries_start)
 	 * it must be *extremely* careful to limit its stack usage.  This
 	 * could include kprobes and a hypothetical future IST-less #DB
 	 * handler.
+	 *
+	 * The OOPS unwinder relies on the word at the top of the IRQ
+	 * stack linking back to the previous RSP for the entire time we're
+	 * on the IRQ stack.  For this to work reliably, we need to write
+	 * it before we actually move ourselves to the IRQ stack.
+	 */
+
+	movq	\old_rsp, PER_CPU_VAR(irq_stack_union + IRQ_STACK_SIZE - 8)
+	movq	PER_CPU_VAR(irq_stack_ptr), %rsp
+
+#ifdef CONFIG_DEBUG_ENTRY
+	/*
+	 * If the first movq above becomes wrong due to IRQ stack layout
+	 * changes, the only way we'll notice is if we try to unwind right
+	 * here.  Assert that we set up the stack right to catch this type
+	 * of bug quickly.
 	 */
+	cmpq	-8(%rsp), \old_rsp
+	je	.Lirq_stack_okay\@
+	ud2
+	.Lirq_stack_okay\@:
+#endif
 
-	cmovzq	PER_CPU_VAR(irq_stack_ptr), %rsp
+.Lirq_stack_push_old_rsp_\@:
 	pushq	\old_rsp
 .endm
 
-- 
2.14.2