f0b89d3958
atomic_t variables are currently used to implement reference counters with the following properties: - counter is initialized to 1 using atomic_set() - a resource is freed upon counter reaching zero - once counter reaches zero, its further increments aren't allowed - counter schema uses basic atomic operations (set, inc, inc_not_zero, dec_and_test, etc.) Such atomic variables should be converted to a newly provided refcount_t type and API that prevents accidental counter overflows and underflows. This is important since overflows and underflows can lead to use-after-free situation and be exploitable. The variable task_struct.stack_refcount is used as pure reference counter. Convert it to refcount_t and fix up the operations. ** Important note for maintainers: Some functions from refcount_t API defined in lib/refcount.c have different memory ordering guarantees than their atomic counterparts. The full comparison can be seen in https://lkml.org/lkml/2017/11/15/57 and it is hopefully soon in state to be merged to the documentation tree. Normally the differences should not matter since refcount_t provides enough guarantees to satisfy the refcounting use cases, but in some rare cases it might matter. Please double check that you don't have some undocumented memory guarantees for this variable usage. For the task_struct.stack_refcount it might make a difference in following places: - try_get_task_stack(): increment in refcount_inc_not_zero() only guarantees control dependency on success vs. fully ordered atomic counterpart - put_task_stack(): decrement in refcount_dec_and_test() only provides RELEASE ordering and control dependency on success vs. fully ordered atomic counterpart Suggested-by: Kees Cook <keescook@chromium.org> Signed-off-by: Elena Reshetova <elena.reshetova@intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: David Windsor <dwindsor@gmail.com> Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com> Reviewed-by: Andrea Parri <andrea.parri@amarulasolutions.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: akpm@linux-foundation.org Cc: viro@zeniv.linux.org.uk Link: https://lkml.kernel.org/r/1547814450-18902-6-git-send-email-elena.reshetova@intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
63 lines
1.6 KiB
C
63 lines
1.6 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX__INIT_TASK_H
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#define _LINUX__INIT_TASK_H
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#include <linux/rcupdate.h>
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#include <linux/irqflags.h>
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#include <linux/utsname.h>
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#include <linux/lockdep.h>
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#include <linux/ftrace.h>
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#include <linux/ipc.h>
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#include <linux/pid_namespace.h>
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#include <linux/user_namespace.h>
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#include <linux/securebits.h>
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#include <linux/seqlock.h>
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#include <linux/rbtree.h>
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#include <linux/refcount.h>
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#include <linux/sched/autogroup.h>
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#include <net/net_namespace.h>
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#include <linux/sched/rt.h>
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#include <linux/livepatch.h>
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#include <linux/mm_types.h>
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#include <asm/thread_info.h>
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extern struct files_struct init_files;
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extern struct fs_struct init_fs;
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extern struct nsproxy init_nsproxy;
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extern struct group_info init_groups;
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extern struct cred init_cred;
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#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
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#define INIT_PREV_CPUTIME(x) .prev_cputime = { \
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.lock = __RAW_SPIN_LOCK_UNLOCKED(x.prev_cputime.lock), \
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},
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#else
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#define INIT_PREV_CPUTIME(x)
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#endif
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#ifdef CONFIG_POSIX_TIMERS
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#define INIT_CPU_TIMERS(s) \
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.cpu_timers = { \
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LIST_HEAD_INIT(s.cpu_timers[0]), \
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LIST_HEAD_INIT(s.cpu_timers[1]), \
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LIST_HEAD_INIT(s.cpu_timers[2]), \
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},
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#else
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#define INIT_CPU_TIMERS(s)
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#endif
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#define INIT_TASK_COMM "swapper"
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/* Attach to the init_task data structure for proper alignment */
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#ifdef CONFIG_ARCH_TASK_STRUCT_ON_STACK
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#define __init_task_data __attribute__((__section__(".data..init_task")))
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#else
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#define __init_task_data /**/
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#endif
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/* Attach to the thread_info data structure for proper alignment */
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#define __init_thread_info __attribute__((__section__(".data..init_thread_info")))
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#endif
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