From d7c816733d501b59dbdc2483f2cc8e4431fd9160 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Wed, 17 Aug 2016 14:42:08 -0700 Subject: list: Split list_add() debug checking into separate function Right now, __list_add() code is repeated either in list.h or in list_debug.c, but the only differences between the two versions are the debug checks. This commit therefore extracts these debug checks into a separate __list_add_valid() function and consolidates __list_add(). Additionally this new __list_add_valid() function 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 Acked-by: Steven Rostedt Signed-off-by: Paul E. McKenney Acked-by: Rik van Riel --- lib/list_debug.c | 48 +++++++++++++++++++++++------------------------- 1 file changed, 23 insertions(+), 25 deletions(-) (limited to 'lib') 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 @@ -13,33 +12,32 @@ #include /* - * 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) { -- cgit v1.2.3 From 54acd4397d7e7a725c94101180cd9f38ef701acc Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Wed, 17 Aug 2016 14:42:09 -0700 Subject: rculist: Consolidate DEBUG_LIST for list_add_rcu() This commit consolidates the debug checking for list_add_rcu() into the new single __list_add_valid() debug function. Notably, this commit fixes the sanity check that was added in commit 17a801f4bfeb ("list_debug: WARN for adding something already in the list"), which wasn't checking RCU-protected lists. Signed-off-by: Kees Cook Acked-by: Steven Rostedt Signed-off-by: Paul E. McKenney Acked-by: Rik van Riel --- include/linux/rculist.h | 8 +++----- lib/list_debug.c | 19 ------------------- 2 files changed, 3 insertions(+), 24 deletions(-) (limited to 'lib') 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); -- cgit v1.2.3 From 0cd340dcb05c4a43742fe156f36737bb2a321bfd Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Wed, 17 Aug 2016 14:42:10 -0700 Subject: list: Split list_del() debug checking into separate function Similar to the list_add() debug consolidation, this commit consolidates the debug checking performed during CONFIG_DEBUG_LIST into a new __list_del_entry_valid() function, and stops list updates when corruption is found. Refactored from same hardening in PaX and Grsecurity. Signed-off-by: Kees Cook Acked-by: Steven Rostedt Signed-off-by: Paul E. McKenney Acked-by: Rik van Riel --- include/linux/list.h | 15 +++++++++------ lib/list_debug.c | 53 +++++++++++++++++++++++----------------------------- 2 files changed, 32 insertions(+), 36 deletions(-) (limited to 'lib') 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); -- cgit v1.2.3 From de54ebbe26bb371a6f1fbc0593372232f04e3107 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Wed, 17 Aug 2016 14:42:11 -0700 Subject: bug: Provide toggle for BUG on data corruption 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 Acked-by: Steven Rostedt Signed-off-by: Paul E. McKenney Acked-by: Rik van Riel --- include/linux/bug.h | 17 ++++++++++++++++ lib/Kconfig.debug | 10 ++++++++++ lib/list_debug.c | 57 +++++++++++++++++++++-------------------------------- 3 files changed, 49 insertions(+), 35 deletions(-) (limited to 'lib') diff --git a/include/linux/bug.h b/include/linux/bug.h index 292d6a10b0c2..baff2e8fc8a8 100644 --- a/include/linux/bug.h +++ b/include/linux/bug.h @@ -121,4 +121,21 @@ 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 33bc56cf60d7..07a6fac930c5 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -1960,6 +1960,16 @@ 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; } -- cgit v1.2.3 From 91a6cee6e30eda815d657d1c2fd4b869fe69d705 Mon Sep 17 00:00:00 2001 From: Valentin Rothberg Date: Sat, 20 Aug 2016 12:16:10 +0200 Subject: lib/Kconfig.debug: Fix typo in select statement Commit 484f29c7430b3 ("bug: Provide toggle for BUG on data corruption") added a Kconfig select statement on CONFIG_DEBUG_LIST, but the CONFIG_ prefix is only used in Make and C(PP) syntax. Remove the CONFIG_ prefix to correctly select the Kconfig option DEBUG_LIST. Signed-off-by: Valentin Rothberg Signed-off-by: Paul E. McKenney Acked-by: Kees Cook --- lib/Kconfig.debug | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'lib') diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 07a6fac930c5..afa30fd52583 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -1962,7 +1962,7 @@ config TEST_STATIC_KEYS config BUG_ON_DATA_CORRUPTION bool "Trigger a BUG when data corruption is detected" - select CONFIG_DEBUG_LIST + select DEBUG_LIST help Select this option if the kernel should BUG when it encounters data corruption in kernel memory structures when they get checked -- cgit v1.2.3 From 4520bcb2ba452863d744337db275c326835fca3f Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Fri, 26 Aug 2016 17:42:00 +0200 Subject: bug: Avoid Kconfig warning for BUG_ON_DATA_CORRUPTION The CONFIG_DEBUG_LIST option is normally meant for kernel developers rather than production machines and is guarded by CONFIG_DEBUG_KERNEL. In contrast, the newly added CONFIG_BUG_ON_DATA_CORRUPTION is meant for security hardening and may be used on systems that intentionally do not enable CONFIG_DEBUG_KERNEL. In this configuration, we get a warning from Kconfig about the mismatched dependencies: warning: (BUG_ON_DATA_CORRUPTION) selects DEBUG_LIST which has unmet direct dependencies (DEBUG_KERNEL) This annotates the DEBUG_LIST option to be selectable by BUG_ON_DATA_CORRUPTION when DEBUG_KERNEL is disabled. Signed-off-by: Arnd Bergmann Fixes: 40cd725cfc7f ("bug: Provide toggle for BUG on data corruption") Acked-by: Rik van Riel Signed-off-by: Paul E. McKenney --- lib/Kconfig.debug | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'lib') diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index afa30fd52583..0c6366b77062 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -1214,7 +1214,7 @@ config DEBUG_BUGVERBOSE config DEBUG_LIST bool "Debug linked list manipulation" - depends on DEBUG_KERNEL + depends on DEBUG_KERNEL || BUG_ON_DATA_CORRUPTION help Enable this to turn on extended checks in the linked-list walking routines. -- cgit v1.2.3 From f2151a0a3436edbed454f48f9f94321eb70e3d2b Mon Sep 17 00:00:00 2001 From: Nikolay Borisov Date: Thu, 6 Oct 2016 05:42:39 -0700 Subject: rcu: RCU_TRACE enables event tracing as well as debugfs The commit brings the RCU_TRACE Kconfig option's help text up to date by noting that it enables additional event tracing as well as debugfs. Signed-off-by: Nikolay Borisov [ paulmck: Do some wordsmithing. ] Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- lib/Kconfig.debug | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'lib') diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 33bc56cf60d7..4a431f18f218 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -1430,7 +1430,8 @@ config RCU_TRACE select TRACE_CLOCK help This option provides tracing in RCU which presents stats - in debugfs for debugging RCU implementation. + in debugfs for debugging RCU implementation. It also enables + additional tracepoints for ftrace-style event tracing. Say Y here if you want to enable RCU tracing Say N if you are unsure. -- cgit v1.2.3