From 3ee01ddf2de536d28625abe0fb49518783ef2d2e Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Thu, 29 Oct 2020 12:10:05 +1100 Subject: [PATCH] mmap locking API: don't check locking if the mm isn't live yet In preparation for adding a mmap_assert_locked() check in __get_user_pages(), teach the mmap_assert_*locked() helpers that it's fine to operate on an mm without locking in the middle of execve() as long as it hasn't been installed on a process yet. Existing code paths that do this are (reverse callgraph): get_user_pages_remote get_arg_page copy_strings copy_string_kernel remove_arg_zero tomoyo_dump_page tomoyo_print_bprm tomoyo_scan_bprm tomoyo_environ Link: https://lkml.kernel.org/r/CAG48ez03YJG9JU_6tGiMcaVjuTyRE_o4LEQ7901b5ZoCnNAjcg@mail.gmail.com Signed-off-by: Jann Horn Cc: "Eric W . Biederman" Cc: Jason Gunthorpe Cc: John Hubbard Cc: Mauro Carvalho Chehab Cc: Michel Lespinasse Cc: Sakari Ailus Signed-off-by: Andrew Morton Signed-off-by: Stephen Rothwell --- fs/exec.c | 8 ++++++++ include/linux/mm_types.h | 10 ++++++++++ include/linux/mmap_lock.h | 16 ++++++++++++---- 3 files changed, 30 insertions(+), 4 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 547a2390baf5..f7009df270aa 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1000,6 +1000,14 @@ static int exec_mmap(struct mm_struct *mm) } } +#if defined(CONFIG_LOCKDEP) || defined(CONFIG_DEBUG_VM) + /* + * From here on, the mm may be accessed concurrently, and proper locking + * is required for things like get_user_pages_remote(). + */ + mm->mmap_lock_required = 1; +#endif + task_lock(tsk); membarrier_exec_mmap(mm); diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 80f5d755c037..6a6b078b9d6a 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -553,6 +553,16 @@ struct mm_struct { #ifdef CONFIG_IOMMU_SUPPORT u32 pasid; #endif + +#if defined(CONFIG_LOCKDEP) || defined(CONFIG_DEBUG_VM) + /* + * Notes whether this mm has been installed on a process yet. + * If not, only the task going through execve() can access this + * mm, and no locking is needed around get_user_pages_remote(). + * This flag is only used for debug checks. + */ + bool mmap_lock_required; +#endif } __randomize_layout; /* diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h index 18e7eae9b5ba..e1afb420fc94 100644 --- a/include/linux/mmap_lock.h +++ b/include/linux/mmap_lock.h @@ -77,14 +77,22 @@ static inline void mmap_read_unlock_non_owner(struct mm_struct *mm) static inline void mmap_assert_locked(struct mm_struct *mm) { - lockdep_assert_held(&mm->mmap_lock); - VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm); +#if defined(CONFIG_LOCKDEP) || defined(CONFIG_DEBUG_VM) + if (mm->mmap_lock_required) { + lockdep_assert_held(&mm->mmap_lock); + VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm); + } +#endif } static inline void mmap_assert_write_locked(struct mm_struct *mm) { - lockdep_assert_held_write(&mm->mmap_lock); - VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm); +#if defined(CONFIG_LOCKDEP) || defined(CONFIG_DEBUG_VM) + if (mm->mmap_lock_required) { + lockdep_assert_held_write(&mm->mmap_lock); + VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm); + } +#endif } static inline int mmap_lock_is_contended(struct mm_struct *mm) -- 2.50.1