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authorJann Horn <jannh@google.com>2020-12-10 15:42:19 +1100
committerStephen Rothwell <sfr@canb.auug.org.au>2020-12-16 18:03:04 +1100
commita263cb22cd048905823a8ddc1ff96a0069a94daa (patch)
tree2c6c61846257fe2cdec56412e0e40b043ebc6dd1
parentfb4adc5c07bc967d9412af785cb90945c4cb16b8 (diff)
downloadlinux-a263cb22cd048905823a8ddc1ff96a0069a94daa.tar.gz
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 <jannh@google.com> Cc: "Eric W . Biederman" <ebiederm@xmission.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Michel Lespinasse <walken@google.com> Cc: Sakari Ailus <sakari.ailus@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
-rw-r--r--fs/exec.c8
-rw-r--r--include/linux/mm_types.h10
-rw-r--r--include/linux/mmap_lock.h16
3 files changed, 30 insertions, 4 deletions
diff --git a/fs/exec.c b/fs/exec.c
index 5d4d52039105..9870163abdc2 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1001,6 +1001,14 @@ 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 07d9acb5b19c..65df8abd90bd 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -561,6 +561,16 @@ 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 0540f0156f58..fe8193d94921 100644
--- a/include/linux/mmap_lock.h
+++ b/include/linux/mmap_lock.h
@@ -161,14 +161,22 @@ 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)