From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>
Date: Tue, 11 Apr 2023 11:10:55 -0400
Subject: [PATCH] mm: enable maple tree RCU mode by default.
References: bsc#1012628
Patch-mainline: 6.2.11
Git-commit: 3dd4432549415f3c65dd52d5c687629efbf4ece1
commit 3dd4432549415f3c65dd52d5c687629efbf4ece1 upstream.
Use the maple tree in RCU mode for VMA tracking.
The maple tree tracks the stack and is able to update the pivot
(lower/upper boundary) in-place to allow the page fault handler to write
to the tree while holding just the mmap read lock. This is safe as the
writes to the stack have a guard VMA which ensures there will always be
a NULL in the direction of the growth and thus will only update a pivot.
It is possible, but not recommended, to have VMAs that grow up/down
without guard VMAs. syzbot has constructed a testcase which sets up a
VMA to grow and consume the empty space. Overwriting the entire NULL
entry causes the tree to be altered in a way that is not safe for
concurrent readers; the readers may see a node being rewritten or one
that does not match the maple state they are using.
Enabling RCU mode allows the concurrent readers to see a stable node and
will return the expected result.
Link: https://lkml.kernel.org/r/20230227173632.3292573-9-surenb@google.com
Cc: stable@vger.kernel.org
Fixes: d4af56c5c7c6 ("mm: start tracking VMAs with maple tree")
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reported-by: syzbot+8d95422d3537159ca390@syzkaller.appspotmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
include/linux/mm_types.h | 3 ++-
kernel/fork.c | 3 +++
mm/mmap.c | 3 ++-
3 files changed, 7 insertions(+), 2 deletions(-)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 9757067c..0e41359d 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -810,7 +810,8 @@ struct mm_struct {
unsigned long cpu_bitmap[];
};
-#define MM_MT_FLAGS (MT_FLAGS_ALLOC_RANGE | MT_FLAGS_LOCK_EXTERN)
+#define MM_MT_FLAGS (MT_FLAGS_ALLOC_RANGE | MT_FLAGS_LOCK_EXTERN | \
+ MT_FLAGS_USE_RCU)
extern struct mm_struct init_mm;
/* Pointer magic because the dynamic array size confuses some compilers. */
diff --git a/kernel/fork.c b/kernel/fork.c
index 8dd0127d..e8808ffb 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -617,6 +617,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
if (retval)
goto out;
+ mt_clear_in_rcu(mas.tree);
mas_for_each(&old_mas, mpnt, ULONG_MAX) {
struct file *file;
@@ -703,6 +704,8 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
retval = arch_dup_mmap(oldmm, mm);
loop_out:
mas_destroy(&mas);
+ if (!retval)
+ mt_set_in_rcu(mas.tree);
out:
mmap_write_unlock(mm);
flush_tlb_mm(oldmm);
diff --git a/mm/mmap.c b/mm/mmap.c
index 425a9349..1931da07 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2308,7 +2308,7 @@ do_mas_align_munmap(struct ma_state *mas, struct vm_area_struct *vma,
int count = 0;
int error = -ENOMEM;
MA_STATE(mas_detach, &mt_detach, 0, 0);
- mt_init_flags(&mt_detach, MT_FLAGS_LOCK_EXTERN);
+ mt_init_flags(&mt_detach, mas->tree->ma_flags & MT_FLAGS_LOCK_MASK);
mt_set_external_lock(&mt_detach, &mm->mmap_lock);
if (mas_preallocate(mas, vma, GFP_KERNEL))
@@ -3095,6 +3095,7 @@ void exit_mmap(struct mm_struct *mm)
*/
set_bit(MMF_OOM_SKIP, &mm->flags);
mmap_write_lock(mm);
+ mt_clear_in_rcu(&mm->mm_mt);
free_pgtables(&tlb, &mm->mm_mt, vma, FIRST_USER_ADDRESS,
USER_PGTABLES_CEILING);
tlb_finish_mmu(&tlb);
--
2.35.3