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[PATCH tip/core/rcu 0/7] RCU list updates for 4.9

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  [PATCH tip/core/rcu 0/7] RCU list updates for 4.9 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-08-22 17:50 +0200
    [PATCH tip/core/rcu 4/7] list: Split list_del() debug checking into separate function "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-08-22 17:50 +0200
    [PATCH tip/core/rcu 3/7] rculist: Consolidate DEBUG_LIST for list_add_rcu() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-08-22 17:50 +0200
    [PATCH tip/core/rcu 1/7] list: Expand list_first_entry_or_null() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-08-22 17:50 +0200
    [PATCH tip/core/rcu 2/7] list: Split list_add() debug checking into separate function "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-08-22 17:50 +0200
    [PATCH tip/core/rcu 5/7] bug: Provide toggle for BUG on data corruption "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-08-22 17:50 +0200

#1467744 — [PATCH tip/core/rcu 0/7] RCU list updates for 4.9

Hello!

This series provides updates to RCU-protected linked lists:

1.	Expand list_first_entry_or_null() to allow better compiler
	optimizations, courtesy of Chris Wilson.

2-6.	Allow security-conscious builds to specify BUG rather than WARN
	for linked-list corruption, courtesy of Kees Cook.

7.	Fix a bogus CONFIG_-prefixed Kconfig-option reference in #5
	above, courtesy of Valentin Rothberg.

							Thanx, Paul

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#1467745 — [PATCH tip/core/rcu 4/7] list: Split list_del() debug checking into separate function

From: Kees Cook <keescook@chromium.org>

Similar to the list_add() debug consolidation, this consolidates the
debug checking performed during CONFIG_DEBUG_LIST, and stops list
updates when corruption is found.

Refactored from same hardening in PaX and Grsecurity.

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Rik van Riel <riel@redhat.com>
---
 include/linux/list.h | 15 +++++++++------
 lib/list_debug.c     | 53 +++++++++++++++++++++++-----------------------------
 2 files changed, 32 insertions(+), 36 deletions(-)

diff --git a/include/linux/list.h b/include/linux/list.h
index b6da9b1dce4d..d1039ecaf94f 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -32,6 +32,7 @@ static inline void INIT_LIST_HEAD(struct list_head *list)
 extern bool __list_add_valid(struct list_head *new,
 			      struct list_head *prev,
 			      struct list_head *next);
+extern bool __list_del_entry_valid(struct list_head *entry);
 #else
 static inline bool __list_add_valid(struct list_head *new,
 				struct list_head *prev,
@@ -39,6 +40,10 @@ static inline bool __list_add_valid(struct list_head *new,
 {
 	return true;
 }
+static inline bool __list_del_entry_valid(struct list_head *entry)
+{
+	return true;
+}
 #endif
 
 /*
@@ -106,22 +111,20 @@ static inline void __list_del(struct list_head * prev, struct list_head * next)
  * Note: list_empty() on entry does not return true after this, the entry is
  * in an undefined state.
  */
-#ifndef CONFIG_DEBUG_LIST
 static inline void __list_del_entry(struct list_head *entry)
 {
+	if (!__list_del_entry_valid(entry))
+		return;
+
 	__list_del(entry->prev, entry->next);
 }
 
 static inline void list_del(struct list_head *entry)
 {
-	__list_del(entry->prev, entry->next);
+	__list_del_entry(entry);
 	entry->next = LIST_POISON1;
 	entry->prev = LIST_POISON2;
 }
-#else
-extern void __list_del_entry(struct list_head *entry);
-extern void list_del(struct list_head *entry);
-#endif
 
 /**
  * list_replace - replace old entry by new one
diff --git a/lib/list_debug.c b/lib/list_debug.c
index d0b89b9d0736..276565fca2a6 100644
--- a/lib/list_debug.c
+++ b/lib/list_debug.c
@@ -39,41 +39,34 @@ bool __list_add_valid(struct list_head *new, struct list_head *prev,
 }
 EXPORT_SYMBOL(__list_add_valid);
 
-void __list_del_entry(struct list_head *entry)
+bool __list_del_entry_valid(struct list_head *entry)
 {
 	struct list_head *prev, *next;
 
 	prev = entry->prev;
 	next = entry->next;
 
-	if (WARN(next == LIST_POISON1,
-		"list_del corruption, %p->next is LIST_POISON1 (%p)\n",
-		entry, LIST_POISON1) ||
-	    WARN(prev == LIST_POISON2,
-		"list_del corruption, %p->prev is LIST_POISON2 (%p)\n",
-		entry, LIST_POISON2) ||
-	    WARN(prev->next != entry,
-		"list_del corruption. prev->next should be %p, "
-		"but was %p\n", entry, prev->next) ||
-	    WARN(next->prev != entry,
-		"list_del corruption. next->prev should be %p, "
-		"but was %p\n", entry, next->prev))
-		return;
-
-	__list_del(prev, next);
-}
-EXPORT_SYMBOL(__list_del_entry);
+	if (unlikely(next == LIST_POISON1)) {
+		WARN(1, "list_del corruption, %p->next is LIST_POISON1 (%p)\n",
+			entry, LIST_POISON1);
+		return false;
+	}
+	if (unlikely(prev == LIST_POISON2)) {
+		WARN(1, "list_del corruption, %p->prev is LIST_POISON2 (%p)\n",
+			entry, LIST_POISON2);
+		return false;
+	}
+	if (unlikely(prev->next != entry)) {
+		WARN(1, "list_del corruption. prev->next should be %p, but was %p\n",
+			entry, prev->next);
+		return false;
+	}
+	if (unlikely(next->prev != entry)) {
+		WARN(1, "list_del corruption. next->prev should be %p, but was %p\n",
+			entry, next->prev);
+		return false;
+	}
+	return true;
 
-/**
- * list_del - deletes entry from list.
- * @entry: the element to delete from the list.
- * Note: list_empty on entry does not return true after this, the entry is
- * in an undefined state.
- */
-void list_del(struct list_head *entry)
-{
-	__list_del_entry(entry);
-	entry->next = LIST_POISON1;
-	entry->prev = LIST_POISON2;
 }
-EXPORT_SYMBOL(list_del);
+EXPORT_SYMBOL(__list_del_entry_valid);
-- 
2.5.2

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#1467748 — [PATCH tip/core/rcu 3/7] rculist: Consolidate DEBUG_LIST for list_add_rcu()

From: Kees Cook <keescook@chromium.org>

Consolidates the debug checking for list_add_rcu() into the new single
debug function. Notably, this fixes the sanity check that was added in
 commit 17a801f4bfeb ("list_debug: WARN for adding something already in
the list"). Before, it wasn't being checked for RCU lists.

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Rik van Riel <riel@redhat.com>
---
 include/linux/rculist.h |  8 +++-----
 lib/list_debug.c        | 19 -------------------
 2 files changed, 3 insertions(+), 24 deletions(-)

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 8beb98dcf14f..4f7a9561b8c4 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -45,19 +45,17 @@ static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
  * This is only for internal list manipulation where we know
  * the prev/next entries already!
  */
-#ifndef CONFIG_DEBUG_LIST
 static inline void __list_add_rcu(struct list_head *new,
 		struct list_head *prev, struct list_head *next)
 {
+	if (!__list_add_valid(new, prev, next))
+		return;
+
 	new->next = next;
 	new->prev = prev;
 	rcu_assign_pointer(list_next_rcu(prev), new);
 	next->prev = new;
 }
-#else
-void __list_add_rcu(struct list_head *new,
-		    struct list_head *prev, struct list_head *next);
-#endif
 
 /**
  * list_add_rcu - add a new entry to rcu-protected list
diff --git a/lib/list_debug.c b/lib/list_debug.c
index 149dd57b583b..d0b89b9d0736 100644
--- a/lib/list_debug.c
+++ b/lib/list_debug.c
@@ -77,22 +77,3 @@ void list_del(struct list_head *entry)
 	entry->prev = LIST_POISON2;
 }
 EXPORT_SYMBOL(list_del);
-
-/*
- * RCU variants.
- */
-void __list_add_rcu(struct list_head *new,
-		    struct list_head *prev, struct list_head *next)
-{
-	WARN(next->prev != prev,
-		"list_add_rcu corruption. next->prev should be prev (%p), but was %p. (next=%p).\n",
-		prev, next->prev, next);
-	WARN(prev->next != next,
-		"list_add_rcu corruption. prev->next should be next (%p), but was %p. (prev=%p).\n",
-		next, prev->next, prev);
-	new->next = next;
-	new->prev = prev;
-	rcu_assign_pointer(list_next_rcu(prev), new);
-	next->prev = new;
-}
-EXPORT_SYMBOL(__list_add_rcu);
-- 
2.5.2

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#1467753 — [PATCH tip/core/rcu 1/7] list: Expand list_first_entry_or_null()

From: Chris Wilson <chris@chris-wilson.co.uk>

Due to the use of READ_ONCE() in list_empty() the compiler cannot
optimise !list_empty() ? list_first_entry() : NULL very well. By
manually expanding list_first_entry_or_null() we can take advantage of
the READ_ONCE() to avoid the list element changing under the test while
the compiler can generate smaller code.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Josef Bacik <jbacik@fb.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/list.h | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/include/linux/list.h b/include/linux/list.h
index 5183138aa932..5809e9a2de5b 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -381,8 +381,11 @@ static inline void list_splice_tail_init(struct list_head *list,
  *
  * Note that if the list is empty, it returns NULL.
  */
-#define list_first_entry_or_null(ptr, type, member) \
-	(!list_empty(ptr) ? list_first_entry(ptr, type, member) : NULL)
+#define list_first_entry_or_null(ptr, type, member) ({ \
+	struct list_head *head__ = (ptr); \
+	struct list_head *pos__ = READ_ONCE(head__->next); \
+	pos__ != head__ ? list_entry(pos__, type, member) : NULL; \
+})
 
 /**
  * list_next_entry - get the next element in list
-- 
2.5.2

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#1467755 — [PATCH tip/core/rcu 2/7] list: Split list_add() debug checking into separate function

From: Kees Cook <keescook@chromium.org>

Right now, __list_add() code is repeated either in list.h or in
list_debug.c, but only the debug checks are the different part. This
extracts the checking into a separate function and consolidates
__list_add(). Additionally this __list_add_debug() will stop list
manipulations if a corruption is detected, instead of allowing for further
corruption that may lead to even worse conditions.

This is slight refactoring of the same hardening done in PaX and Grsecurity.

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Rik van Riel <riel@redhat.com>
---
 include/linux/list.h | 22 ++++++++++++++++------
 lib/list_debug.c     | 48 +++++++++++++++++++++++-------------------------
 2 files changed, 39 insertions(+), 31 deletions(-)

diff --git a/include/linux/list.h b/include/linux/list.h
index 5809e9a2de5b..b6da9b1dce4d 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -28,27 +28,37 @@ static inline void INIT_LIST_HEAD(struct list_head *list)
 	list->prev = list;
 }
 
+#ifdef CONFIG_DEBUG_LIST
+extern bool __list_add_valid(struct list_head *new,
+			      struct list_head *prev,
+			      struct list_head *next);
+#else
+static inline bool __list_add_valid(struct list_head *new,
+				struct list_head *prev,
+				struct list_head *next)
+{
+	return true;
+}
+#endif
+
 /*
  * Insert a new entry between two known consecutive entries.
  *
  * This is only for internal list manipulation where we know
  * the prev/next entries already!
  */
-#ifndef CONFIG_DEBUG_LIST
 static inline void __list_add(struct list_head *new,
 			      struct list_head *prev,
 			      struct list_head *next)
 {
+	if (!__list_add_valid(new, prev, next))
+		return;
+
 	next->prev = new;
 	new->next = next;
 	new->prev = prev;
 	WRITE_ONCE(prev->next, new);
 }
-#else
-extern void __list_add(struct list_head *new,
-			      struct list_head *prev,
-			      struct list_head *next);
-#endif
 
 /**
  * list_add - add a new entry
diff --git a/lib/list_debug.c b/lib/list_debug.c
index 3859bf63561c..149dd57b583b 100644
--- a/lib/list_debug.c
+++ b/lib/list_debug.c
@@ -2,8 +2,7 @@
  * Copyright 2006, Red Hat, Inc., Dave Jones
  * Released under the General Public License (GPL).
  *
- * This file contains the linked list implementations for
- * DEBUG_LIST.
+ * This file contains the linked list validation for DEBUG_LIST.
  */
 
 #include <linux/export.h>
@@ -13,33 +12,32 @@
 #include <linux/rculist.h>
 
 /*
- * Insert a new entry between two known consecutive entries.
- *
- * This is only for internal list manipulation where we know
- * the prev/next entries already!
+ * Check that the data structures for the list manipulations are reasonably
+ * valid. Failures here indicate memory corruption (and possibly an exploit
+ * attempt).
  */
 
-void __list_add(struct list_head *new,
-			      struct list_head *prev,
-			      struct list_head *next)
+bool __list_add_valid(struct list_head *new, struct list_head *prev,
+		      struct list_head *next)
 {
-	WARN(next->prev != prev,
-		"list_add corruption. next->prev should be "
-		"prev (%p), but was %p. (next=%p).\n",
-		prev, next->prev, next);
-	WARN(prev->next != next,
-		"list_add corruption. prev->next should be "
-		"next (%p), but was %p. (prev=%p).\n",
-		next, prev->next, prev);
-	WARN(new == prev || new == next,
-	     "list_add double add: new=%p, prev=%p, next=%p.\n",
-	     new, prev, next);
-	next->prev = new;
-	new->next = next;
-	new->prev = prev;
-	WRITE_ONCE(prev->next, new);
+	if (unlikely(next->prev != prev)) {
+		WARN(1, "list_add corruption. next->prev should be prev (%p), but was %p. (next=%p).\n",
+			prev, next->prev, next);
+		return false;
+	}
+	if (unlikely(prev->next != next)) {
+		WARN(1, "list_add corruption. prev->next should be next (%p), but was %p. (prev=%p).\n",
+			next, prev->next, prev);
+		return false;
+	}
+	if (unlikely(new == prev || new == next)) {
+		WARN(1, "list_add double add: new=%p, prev=%p, next=%p.\n",
+			new, prev, next);
+		return false;
+	}
+	return true;
 }
-EXPORT_SYMBOL(__list_add);
+EXPORT_SYMBOL(__list_add_valid);
 
 void __list_del_entry(struct list_head *entry)
 {
-- 
2.5.2

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#1467760 — [PATCH tip/core/rcu 5/7] bug: Provide toggle for BUG on data corruption

From: Kees Cook <keescook@chromium.org>

The kernel checks for cases of data structure corruption under some
CONFIGs (e.g. CONFIG_DEBUG_LIST). When corruption is detected, some
systems may want to BUG() immediately instead of letting the system run
with known corruption.  Usually these kinds of manipulation primitives can
be used by security flaws to gain arbitrary memory write control. This
provides a new config CONFIG_BUG_ON_DATA_CORRUPTION and a corresponding
macro CHECK_DATA_CORRUPTION for handling these situations. Notably, even
if not BUGing, the kernel should not continue processing the corrupted
structure.

This is inspired by similar hardening by Syed Rameez Mustafa in MSM
kernels, and in PaX and Grsecurity, which is likely in response to earlier
removal of the BUG calls in commit 924d9addb9b1 ("list debugging: use
WARN() instead of BUG()").

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Rik van Riel <riel@redhat.com>
---
 include/linux/bug.h | 17 ++++++++++++++++
 lib/Kconfig.debug   | 10 ++++++++++
 lib/list_debug.c    | 57 +++++++++++++++++++++--------------------------------
 3 files changed, 49 insertions(+), 35 deletions(-)

diff --git a/include/linux/bug.h b/include/linux/bug.h
index e51b0709e78d..51a486f4eb4c 100644
--- a/include/linux/bug.h
+++ b/include/linux/bug.h
@@ -118,4 +118,21 @@ static inline enum bug_trap_type report_bug(unsigned long bug_addr,
 }
 
 #endif	/* CONFIG_GENERIC_BUG */
+
+/*
+ * Since detected data corruption should stop operation on the affected
+ * structures, this returns false if the corruption condition is found.
+ */
+#define CHECK_DATA_CORRUPTION(condition, fmt, ...)			 \
+	do {								 \
+		if (unlikely(condition)) {				 \
+			if (IS_ENABLED(CONFIG_BUG_ON_DATA_CORRUPTION)) { \
+				pr_err(fmt, ##__VA_ARGS__);		 \
+				BUG();					 \
+			} else						 \
+				WARN(1, fmt, ##__VA_ARGS__);		 \
+			return false;					 \
+		}							 \
+	} while (0)
+
 #endif	/* _LINUX_BUG_H */
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 2307d7c89dac..58d358a4c7f3 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1987,6 +1987,16 @@ config TEST_STATIC_KEYS
 
 	  If unsure, say N.
 
+config BUG_ON_DATA_CORRUPTION
+	bool "Trigger a BUG when data corruption is detected"
+	select CONFIG_DEBUG_LIST
+	help
+	  Select this option if the kernel should BUG when it encounters
+	  data corruption in kernel memory structures when they get checked
+	  for validity.
+
+	  If unsure, say N.
+
 source "samples/Kconfig"
 
 source "lib/Kconfig.kgdb"
diff --git a/lib/list_debug.c b/lib/list_debug.c
index 276565fca2a6..7f7bfa55eb6d 100644
--- a/lib/list_debug.c
+++ b/lib/list_debug.c
@@ -20,21 +20,16 @@
 bool __list_add_valid(struct list_head *new, struct list_head *prev,
 		      struct list_head *next)
 {
-	if (unlikely(next->prev != prev)) {
-		WARN(1, "list_add corruption. next->prev should be prev (%p), but was %p. (next=%p).\n",
-			prev, next->prev, next);
-		return false;
-	}
-	if (unlikely(prev->next != next)) {
-		WARN(1, "list_add corruption. prev->next should be next (%p), but was %p. (prev=%p).\n",
-			next, prev->next, prev);
-		return false;
-	}
-	if (unlikely(new == prev || new == next)) {
-		WARN(1, "list_add double add: new=%p, prev=%p, next=%p.\n",
-			new, prev, next);
-		return false;
-	}
+	CHECK_DATA_CORRUPTION(next->prev != prev,
+		"list_add corruption. next->prev should be prev (%p), but was %p. (next=%p).\n",
+		prev, next->prev, next);
+	CHECK_DATA_CORRUPTION(prev->next != next,
+		"list_add corruption. prev->next should be next (%p), but was %p. (prev=%p).\n",
+		next, prev->next, prev);
+	CHECK_DATA_CORRUPTION(new == prev || new == next,
+		"list_add double add: new=%p, prev=%p, next=%p.\n",
+		new, prev, next);
+
 	return true;
 }
 EXPORT_SYMBOL(__list_add_valid);
@@ -46,26 +41,18 @@ bool __list_del_entry_valid(struct list_head *entry)
 	prev = entry->prev;
 	next = entry->next;
 
-	if (unlikely(next == LIST_POISON1)) {
-		WARN(1, "list_del corruption, %p->next is LIST_POISON1 (%p)\n",
-			entry, LIST_POISON1);
-		return false;
-	}
-	if (unlikely(prev == LIST_POISON2)) {
-		WARN(1, "list_del corruption, %p->prev is LIST_POISON2 (%p)\n",
-			entry, LIST_POISON2);
-		return false;
-	}
-	if (unlikely(prev->next != entry)) {
-		WARN(1, "list_del corruption. prev->next should be %p, but was %p\n",
-			entry, prev->next);
-		return false;
-	}
-	if (unlikely(next->prev != entry)) {
-		WARN(1, "list_del corruption. next->prev should be %p, but was %p\n",
-			entry, next->prev);
-		return false;
-	}
+	CHECK_DATA_CORRUPTION(next == LIST_POISON1,
+		"list_del corruption, %p->next is LIST_POISON1 (%p)\n",
+		entry, LIST_POISON1);
+	CHECK_DATA_CORRUPTION(prev == LIST_POISON2,
+		"list_del corruption, %p->prev is LIST_POISON2 (%p)\n",
+		entry, LIST_POISON2);
+	CHECK_DATA_CORRUPTION(prev->next != entry,
+		"list_del corruption. prev->next should be %p, but was %p\n",
+		entry, prev->next);
+	CHECK_DATA_CORRUPTION(next->prev != entry,
+		"list_del corruption. next->prev should be %p, but was %p\n",
+		entry, next->prev);
 	return true;
 
 }
-- 
2.5.2

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