diff options
author | Peter Zijlstra <peterz@infradead.org> | 2017-12-14 14:27:30 +0300 |
---|---|---|
committer | Ingo Molnar <mingo@kernel.org> | 2017-12-22 22:13:01 +0300 |
commit | c2b3496bb30bd159e9de42e5c952e1f1f33c9a77 (patch) | |
tree | d1617d48b0546def2ea19bc4a6fa3e1637e1f6ed /arch/x86/kernel/ldt.c | |
parent | c10e83f598d08046dd1ebc8360d4bb12d802d51b (diff) | |
download | linux-c2b3496bb30bd159e9de42e5c952e1f1f33c9a77.tar.xz |
x86/ldt: Rework locking
The LDT is duplicated on fork() and on exec(), which is wrong as exec()
should start from a clean state, i.e. without LDT. To fix this the LDT
duplication code will be moved into arch_dup_mmap() which is only called
for fork().
This introduces a locking problem. arch_dup_mmap() holds mmap_sem of the
parent process, but the LDT duplication code needs to acquire
mm->context.lock to access the LDT data safely, which is the reverse lock
order of write_ldt() where mmap_sem nests into context.lock.
Solve this by introducing a new rw semaphore which serializes the
read/write_ldt() syscall operations and use context.lock to protect the
actual installment of the LDT descriptor.
So context.lock stabilizes mm->context.ldt and can nest inside of the new
semaphore or mmap_sem.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirsky <luto@kernel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Laight <David.Laight@aculab.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Eduardo Valentin <eduval@amazon.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: aliguori@amazon.com
Cc: dan.j.williams@intel.com
Cc: hughd@google.com
Cc: keescook@google.com
Cc: kirill.shutemov@linux.intel.com
Cc: linux-mm@kvack.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/kernel/ldt.c')
-rw-r--r-- | arch/x86/kernel/ldt.c | 33 |
1 files changed, 21 insertions, 12 deletions
diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c index 1c1eae961340..1600aebc1ec7 100644 --- a/arch/x86/kernel/ldt.c +++ b/arch/x86/kernel/ldt.c @@ -5,6 +5,11 @@ * Copyright (C) 2002 Andi Kleen * * This handles calls from both 32bit and 64bit mode. + * + * Lock order: + * contex.ldt_usr_sem + * mmap_sem + * context.lock */ #include <linux/errno.h> @@ -42,7 +47,7 @@ static void refresh_ldt_segments(void) #endif } -/* context.lock is held for us, so we don't need any locking. */ +/* context.lock is held by the task which issued the smp function call */ static void flush_ldt(void *__mm) { struct mm_struct *mm = __mm; @@ -99,15 +104,17 @@ static void finalize_ldt_struct(struct ldt_struct *ldt) paravirt_alloc_ldt(ldt->entries, ldt->nr_entries); } -/* context.lock is held */ -static void install_ldt(struct mm_struct *current_mm, - struct ldt_struct *ldt) +static void install_ldt(struct mm_struct *mm, struct ldt_struct *ldt) { + mutex_lock(&mm->context.lock); + /* Synchronizes with READ_ONCE in load_mm_ldt. */ - smp_store_release(¤t_mm->context.ldt, ldt); + smp_store_release(&mm->context.ldt, ldt); - /* Activate the LDT for all CPUs using current_mm. */ - on_each_cpu_mask(mm_cpumask(current_mm), flush_ldt, current_mm, true); + /* Activate the LDT for all CPUs using currents mm. */ + on_each_cpu_mask(mm_cpumask(mm), flush_ldt, mm, true); + + mutex_unlock(&mm->context.lock); } static void free_ldt_struct(struct ldt_struct *ldt) @@ -133,7 +140,8 @@ int init_new_context_ldt(struct task_struct *tsk, struct mm_struct *mm) struct mm_struct *old_mm; int retval = 0; - mutex_init(&mm->context.lock); + init_rwsem(&mm->context.ldt_usr_sem); + old_mm = current->mm; if (!old_mm) { mm->context.ldt = NULL; @@ -180,7 +188,7 @@ static int read_ldt(void __user *ptr, unsigned long bytecount) unsigned long entries_size; int retval; - mutex_lock(&mm->context.lock); + down_read(&mm->context.ldt_usr_sem); if (!mm->context.ldt) { retval = 0; @@ -209,7 +217,7 @@ static int read_ldt(void __user *ptr, unsigned long bytecount) retval = bytecount; out_unlock: - mutex_unlock(&mm->context.lock); + up_read(&mm->context.ldt_usr_sem); return retval; } @@ -269,7 +277,8 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode) ldt.avl = 0; } - mutex_lock(&mm->context.lock); + if (down_write_killable(&mm->context.ldt_usr_sem)) + return -EINTR; old_ldt = mm->context.ldt; old_nr_entries = old_ldt ? old_ldt->nr_entries : 0; @@ -291,7 +300,7 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode) error = 0; out_unlock: - mutex_unlock(&mm->context.lock); + up_write(&mm->context.ldt_usr_sem); out: return error; } |