mm, mmap: fix vma_merge() case 7 with vma_ops->close

commit fc0c8f9089c20d198d8fe51ddc28bfa1af588dce upstream.

When debugging issues with a workload using SysV shmem, Michal Hocko has
come up with

mm, mmap: fix vma_merge() case 7 with vma_ops->close

commit fc0c8f9089c20d198d8fe51ddc28bfa1af588dce upstream.

When debugging issues with a workload using SysV shmem, Michal Hocko has
come up with a reproducer that shows how a series of mprotect() operations
can result in an elevated shm_nattch and thus leak of the resource.

The problem is caused by wrong assumptions in vma_merge() commit
714965ca8252 ("mm/mmap: start distinguishing if vma can be removed in
mergeability test"). The shmem vmas have a vma_ops->close callback that
decrements shm_nattch, and we remove the vma without calling it.

vma_merge() has thus historically avoided merging vma's with
vma_ops->close and commit 714965ca8252 was supposed to keep it that way.
It relaxed the checks for vma_ops->close in can_vma_merge_after() assuming
that it is never called on a vma that would be a candidate for removal.
However, the vma_merge() code does also use the result of this check in
the decision to remove a different vma in the merge case 7.

A robust solution would be to refactor vma_merge() code in a way that the
vma_ops->close check is only done for vma's that are actually going to be
removed, and not as part of the preliminary checks. That would both solve
the existing bug, and also allow additional merges that the checks
currently prevent unnecessarily in some cases.

However to fix the existing bug first with a minimized risk, and for
easier stable backports, this patch only adds a vma_ops->close check to
the buggy case 7 specifically. All other cases of vma removal are covered
by the can_vma_merge_before() check that includes the test for
vma_ops->close.

The reproducer code, adapted from Michal Hocko's code:

int main(int argc, char *argv[]) {
int segment_id;
size_t segment_size = 20 * PAGE_SIZE;
char * sh_mem;
struct shmid_ds shmid_ds;

key_t key = 0x1234;
segment_id = shmget(key, segment_size,
IPC_CREAT | IPC_EXCL | S_IRUSR | S_IWUSR);
sh_mem = (char *)shmat(segment_id, NULL, 0);

mprotect(sh_mem + 2*PAGE_SIZE, PAGE_SIZE, PROT_NONE);

mprotect(sh_mem + PAGE_SIZE, PAGE_SIZE, PROT_WRITE);

mprotect(sh_mem + 2*PAGE_SIZE, PAGE_SIZE, PROT_WRITE);

shmdt(sh_mem);

shmctl(segment_id, IPC_STAT, &shmid_ds);
printf("nattch after shmdt(): %lu (expected: 0)\n", shmid_ds.shm_nattch);

if (shmctl(segment_id, IPC_RMID, 0))
printf("IPCRM failed %d\n", errno);
return (shmid_ds.shm_nattch) ? 1 : 0;
}

Link: https://lkml.kernel.org/r/20240222215930.14637-2-vbabka@suse.cz
Fixes: 714965ca8252 ("mm/mmap: start distinguishing if vma can be removed in mergeability test")
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Reported-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

show more ...

mm, mmap: fix vma_merge() case 7 with vma_ops->close

commit fc0c8f9089c20d198d8fe51ddc28bfa1af588dce upstream.

When debugging issues with a workload using SysV shmem, Michal Hocko has
come up with

mm, mmap: fix vma_merge() case 7 with vma_ops->close

commit fc0c8f9089c20d198d8fe51ddc28bfa1af588dce upstream.

When debugging issues with a workload using SysV shmem, Michal Hocko has
come up with a reproducer that shows how a series of mprotect() operations
can result in an elevated shm_nattch and thus leak of the resource.

The problem is caused by wrong assumptions in vma_merge() commit
714965ca8252 ("mm/mmap: start distinguishing if vma can be removed in
mergeability test"). The shmem vmas have a vma_ops->close callback that
decrements shm_nattch, and we remove the vma without calling it.

vma_merge() has thus historically avoided merging vma's with
vma_ops->close and commit 714965ca8252 was supposed to keep it that way.
It relaxed the checks for vma_ops->close in can_vma_merge_after() assuming
that it is never called on a vma that would be a candidate for removal.
However, the vma_merge() code does also use the result of this check in
the decision to remove a different vma in the merge case 7.

A robust solution would be to refactor vma_merge() code in a way that the
vma_ops->close check is only done for vma's that are actually going to be
removed, and not as part of the preliminary checks. That would both solve
the existing bug, and also allow additional merges that the checks
currently prevent unnecessarily in some cases.

However to fix the existing bug first with a minimized risk, and for
easier stable backports, this patch only adds a vma_ops->close check to
the buggy case 7 specifically. All other cases of vma removal are covered
by the can_vma_merge_before() check that includes the test for
vma_ops->close.

The reproducer code, adapted from Michal Hocko's code:

int main(int argc, char *argv[]) {
int segment_id;
size_t segment_size = 20 * PAGE_SIZE;
char * sh_mem;
struct shmid_ds shmid_ds;

key_t key = 0x1234;
segment_id = shmget(key, segment_size,
IPC_CREAT | IPC_EXCL | S_IRUSR | S_IWUSR);
sh_mem = (char *)shmat(segment_id, NULL, 0);

mprotect(sh_mem + 2*PAGE_SIZE, PAGE_SIZE, PROT_NONE);

mprotect(sh_mem + PAGE_SIZE, PAGE_SIZE, PROT_WRITE);

mprotect(sh_mem + 2*PAGE_SIZE, PAGE_SIZE, PROT_WRITE);

shmdt(sh_mem);

shmctl(segment_id, IPC_STAT, &shmid_ds);
printf("nattch after shmdt(): %lu (expected: 0)\n", shmid_ds.shm_nattch);

if (shmctl(segment_id, IPC_RMID, 0))
printf("IPCRM failed %d\n", errno);
return (shmid_ds.shm_nattch) ? 1 : 0;
}

Link: https://lkml.kernel.org/r/20240222215930.14637-2-vbabka@suse.cz
Fixes: 714965ca8252 ("mm/mmap: start distinguishing if vma can be removed in mergeability test")
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Reported-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

show more ...

mmap: fix error paths with dup_anon_vma()

When the calling function fails after the dup_anon_vma(), the
duplication of the anon_vma is not being undone. Add the necessary
unlink_anon_vma() call to

mmap: fix error paths with dup_anon_vma()

When the calling function fails after the dup_anon_vma(), the
duplication of the anon_vma is not being undone. Add the necessary
unlink_anon_vma() call to the error paths that are missing them.

This issue showed up during inspection of the error path in vma_merge()
for an unrelated vma iterator issue.

Users may experience increased memory usage, which may be problematic as
the failure would likely be caused by a low memory situation.

Link: https://lkml.kernel.org/r/20230929183041.2835469-3-Liam.Howlett@oracle.com
Fixes: d4af56c5c7c6 ("mm: start tracking VMAs with maple tree")
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

show more ...

mmap: fix vma_iterator in error path of vma_merge()

During the error path, the vma iterator may not be correctly positioned or
set to the correct range. Undo the vma_prev() call by resetting to the

mmap: fix vma_iterator in error path of vma_merge()

During the error path, the vma iterator may not be correctly positioned or
set to the correct range. Undo the vma_prev() call by resetting to the
passed in address. Re-walking to the same range will fix the range to the
area previously passed in.

Users would notice increased cycles as vma_merge() would be called an
extra time with vma == prev, and thus would fail to merge and return.

Link: https://lore.kernel.org/linux-mm/CAG48ez12VN1JAOtTNMY+Y2YnsU45yL5giS-Qn=ejtiHpgJAbdQ@mail.gmail.com/
Link: https://lkml.kernel.org/r/20230929183041.2835469-2-Liam.Howlett@oracle.com
Fixes: 18b098af2890 ("vma_merge: set vma iterator to correct position.")
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reported-by: Jann Horn <jannh@google.com>
Closes: https://lore.kernel.org/linux-mm/CAG48ez12VN1JAOtTNMY+Y2YnsU45yL5giS-Qn=ejtiHpgJAbdQ@mail.gmail.com/
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

show more ...

mm: fix vm_brk_flags() to not bail out while holding lock

Calling vm_brk_flags() with flags set other than VM_EXEC will exit the
function without releasing the mmap_write_lock.

Just do the sanity c

mm: fix vm_brk_flags() to not bail out while holding lock

Calling vm_brk_flags() with flags set other than VM_EXEC will exit the
function without releasing the mmap_write_lock.

Just do the sanity check before the lock is acquired. This doesn't fix an
actual issue since no caller sets a flag other than VM_EXEC.

Link: https://lkml.kernel.org/r/20230929171937.work.697-kees@kernel.org
Fixes: 2e7ce7d354f2 ("mm/mmap: change do_brk_flags() to expand existing VMA and add do_brk_munmap()")
Signed-off-by: Sebastian Ott <sebott@redhat.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

show more ...

mm: move vma locking out of vma_prepare and dup_anon_vma

vma_prepare() is currently the central place where vmas are being locked
before vma_complete() applies changes to them. While this is conveni

mm: move vma locking out of vma_prepare and dup_anon_vma

vma_prepare() is currently the central place where vmas are being locked
before vma_complete() applies changes to them. While this is convenient,
it also obscures vma locking and makes it harder to follow the locking
rules. Move vma locking out of vma_prepare() and take vma locks
explicitly at the locations where vmas are being modified. Move vma
locking and replace it with an assertion inside dup_anon_vma() to further
clarify the locking pattern inside vma_merge().

Link: https://lkml.kernel.org/r/20230804152724.3090321-7-surenb@google.com
Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
Suggested-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

show more ...

mm: always lock new vma before inserting into vma tree

While it's not strictly necessary to lock a newly created vma before
adding it into the vma tree (as long as no further changes are performed
t

mm: always lock new vma before inserting into vma tree

While it's not strictly necessary to lock a newly created vma before
adding it into the vma tree (as long as no further changes are performed
to it), it seems like a good policy to lock it and prevent accidental
changes after it becomes visible to the page faults. Lock the vma before
adding it into the vma tree.

[akpm@linux-foundation.org: fix reject fixing in vma_link(), per Jann]
Link: https://lkml.kernel.org/r/20230804152724.3090321-6-surenb@google.com
Suggested-by: Jann Horn <jannh@google.com>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Linus Torvalds <torvalds@linuxfoundation.org>
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

show more ...

mm/mmap.c: use helper macro K()

Use helper macro K() to improve code readability. No functional
modification involved.

Link: https://lkml.kernel.org/r/20230804012559.2617515-7-zhangpeng362@huawei.

mm/mmap.c: use helper macro K()

Use helper macro K() to improve code readability. No functional
modification involved.

Link: https://lkml.kernel.org/r/20230804012559.2617515-7-zhangpeng362@huawei.com
Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

show more ...

mm/mmap: change vma iteration order in do_vmi_align_munmap()

By delaying the setting of prev/next VMA until after the write of NULL,
the probability of the prev/next VMA already being in the CPU cac

mm/mmap: change vma iteration order in do_vmi_align_munmap()

By delaying the setting of prev/next VMA until after the write of NULL,
the probability of the prev/next VMA already being in the CPU cache is
significantly increased, especially for larger munmap operations. It
also means that prev/next will be loaded closer to when they are used.

This requires changing the loop type when gathering the VMAs that will
be freed.

Since prev will be set later in the function, it is better to reverse
the splitting direction of the start VMA (modify the new_below argument
to __split_vma).

Using the vma_iter_prev_range() to walk back to the correct location in
the tree will, on the most part, mean walking within the CPU cache.
Usually, this is two steps vs a node reset and a tree re-walk.

Link: https://lkml.kernel.org/r/20230724183157.3939892-16-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

show more ...

mm: set up vma iterator for vma_iter_prealloc() calls

Set the correct limits for vma_iter_prealloc() calls so that the maple
tree can be smarter about how many nodes are needed.

Link: https://lkml.

mm: set up vma iterator for vma_iter_prealloc() calls

Set the correct limits for vma_iter_prealloc() calls so that the maple
tree can be smarter about how many nodes are needed.

Link: https://lkml.kernel.org/r/20230724183157.3939892-11-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

show more ...

mm: use vma_iter_clear_gfp() in nommu

Move the definition of vma_iter_clear_gfp() from mmap.c to internal.h so
it can be used in the nommu code. This will reduce node preallocations
in nommu.

Link

mm: use vma_iter_clear_gfp() in nommu

Move the definition of vma_iter_clear_gfp() from mmap.c to internal.h so
it can be used in the nommu code. This will reduce node preallocations
in nommu.

Link: https://lkml.kernel.org/r/20230724183157.3939892-10-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

show more ...

maple_tree: re-introduce entry to mas_preallocate() arguments

The current preallocation strategy is to preallocate the absolute
worst-case allocation for a tree modification. The entry (or NULL) is

maple_tree: re-introduce entry to mas_preallocate() arguments

The current preallocation strategy is to preallocate the absolute
worst-case allocation for a tree modification. The entry (or NULL) is
needed to know how many nodes are needed to write to the tree. Start by
adding the argument to the mas_preallocate() definition.

Link: https://lkml.kernel.org/r/20230724183157.3939892-8-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

show more ...

mm: remove re-walk from mmap_region()

Using vma_iter_set() will reset the tree and cause a re-walk. Use
vmi_iter_config() to set the write to a sub-set of the range. Change
the file case to also u

mm: remove re-walk from mmap_region()

Using vma_iter_set() will reset the tree and cause a re-walk. Use
vmi_iter_config() to set the write to a sub-set of the range. Change
the file case to also use vmi_iter_config() so that the end is correctly
set.

Link: https://lkml.kernel.org/r/20230724183157.3939892-7-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

show more ...

mm: remove prev check from do_vmi_align_munmap()

If the prev does not exist, the vma iterator will be set to MAS_NONE,
which will be treated as a MAS_START when the mas_next or mas_find is
used. In

mm: remove prev check from do_vmi_align_munmap()

If the prev does not exist, the vma iterator will be set to MAS_NONE,
which will be treated as a MAS_START when the mas_next or mas_find is
used. In this case, the next caller will be the vma iterator, which
uses mas_find() under the hood and will now do what the user expects.

Link: https://lkml.kernel.org/r/20230724183157.3939892-5-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

show more ...

mm: change do_vmi_align_munmap() tracking of VMAs to remove

The majority of the calls to munmap a vm range is within a single vma.
The maple tree is able to store a single entry at 0, with a size of

mm: change do_vmi_align_munmap() tracking of VMAs to remove

The majority of the calls to munmap a vm range is within a single vma.
The maple tree is able to store a single entry at 0, with a size of 1 as
a pointer and avoid any allocations. Change do_vmi_align_munmap() to
store the VMAs being munmap()'ed into a tree indexed by the count. This
will leverage the ability to store the first entry without a node
allocation.

Storing the entries into a tree by the count and not the vma start and
end means changing the functions which iterate over the entries. Update
unmap_vmas() and free_pgtables() to take a maple state and a tree end
address to support this functionality.

Passing through the same maple state to unmap_vmas() and free_pgtables()
means the state needs to be reset between calls. This happens in the
static unmap_region() and exit_mmap().

Link: https://lkml.kernel.org/r/20230724183157.3939892-4-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

show more ...

mm: don't drop VMA locks in mm_drop_all_locks()

Despite its name, mm_drop_all_locks() does not drop _all_ locks; the mmap
lock is held write-locked by the caller, and the caller is responsible for
d

mm: don't drop VMA locks in mm_drop_all_locks()

Despite its name, mm_drop_all_locks() does not drop _all_ locks; the mmap
lock is held write-locked by the caller, and the caller is responsible for
dropping the mmap lock at a later point (which will also release the VMA
locks).

Calling vma_end_write_all() here is dangerous because the caller might
have write-locked a VMA with the expectation that it will stay
write-locked until the mmap_lock is released, as usual.

This _almost_ becomes a problem in the following scenario:

An anonymous VMA A and an SGX VMA B are mapped adjacent to each other.
Userspace calls munmap() on a range starting at the start address of A and
ending in the middle of B.

Hypothetical call graph with additional notes in brackets:

do_vmi_align_munmap
[begin first for_each_vma_range loop]
vma_start_write [on VMA A]
vma_mark_detached [on VMA A]
__split_vma [on VMA B]
sgx_vma_open [== new->vm_ops->open]
sgx_encl_mm_add
__mmu_notifier_register [luckily THIS CAN'T ACTUALLY HAPPEN]
mm_take_all_locks
mm_drop_all_locks
vma_end_write_all [drops VMA lock taken on VMA A before]
vma_start_write [on VMA B]
vma_mark_detached [on VMA B]
[end first for_each_vma_range loop]
vma_iter_clear_gfp [removes VMAs from maple tree]
mmap_write_downgrade
unmap_region
mmap_read_unlock

In this hypothetical scenario, while do_vmi_align_munmap() thinks it still
holds a VMA write lock on VMA A, the VMA write lock has actually been
invalidated inside __split_vma().

The call from sgx_encl_mm_add() to __mmu_notifier_register() can't
actually happen here, as far as I understand, because we are duplicating
an existing SGX VMA, but sgx_encl_mm_add() only calls
__mmu_notifier_register() for the first SGX VMA created in a given
process. So this could only happen in fork(), not on munmap(). But in my
view it is just pure luck that this can't happen.

Also, we wouldn't actually have any bad consequences from this in
do_vmi_align_munmap(), because by the time the bug drops the lock on VMA
A, we've already marked VMA A as detached, which makes it completely
ineligible for any VMA-locked page faults. But again, that's just pure
luck.

So remove the vma_end_write_all(), so that VMA write locks are only ever
released on mmap_write_unlock() or mmap_write_downgrade().

Also add comments to document the locking rules established by this patch.

Link: https://lkml.kernel.org/r/20230720193436.454247-1-jannh@google.com
Fixes: eeff9a5d47f8 ("mm/mmap: prevent pagefault handler from racing with mmu_notifier registration")
Signed-off-by: Jann Horn <jannh@google.com>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

show more ...

mm/mmap: change detached vma locking scheme

Don't set the lock to the mm lock so that the detached VMA tree does not
complain about being unlocked when the mmap_lock is dropped prior to
freeing the

mm/mmap: change detached vma locking scheme

Don't set the lock to the mm lock so that the detached VMA tree does not
complain about being unlocked when the mmap_lock is dropped prior to
freeing the tree.

Introduce mt_on_stack() for setting the external lock to NULL only when
LOCKDEP is used.

Move the destroying of the detached tree outside the mmap lock all
together.

Link: https://lkml.kernel.org/r/20230719183142.ktgcmuj2pnlr3h3s@revolver
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oliver Sang <oliver.sang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

show more ...

mm/mmap: clean up validate_mm() calls

Patch series "More strict maple tree lockdep", v2.

Linus asked for more strict maple tree lockdep checking [1] and for them
to resume the normal path through A

mm/mmap: clean up validate_mm() calls

Patch series "More strict maple tree lockdep", v2.

Linus asked for more strict maple tree lockdep checking [1] and for them
to resume the normal path through Andrews tree.

This series of patches adds checks to ensure the lock is held in write
mode during the write path of the maple tree instead of checking if it's
held at all.

It also reduces the validate_mm() calls by consolidating into commonly
used functions (patch 0001), and removes the necessity of holding the lock
on the detached tree during munmap() operations.


This patch (of 4):

validate_mm() calls are too spread out and duplicated in numerous
locations. Also, now that the stack write is done under the write lock,
it is not necessary to validate the mm prior to write operations.

Add a validate_mm() to the stack expansions, and to vma_complete() so
that numerous others may be dropped.

Note that vma_link() (and also insert_vm_struct() by call path) already
call validate_mm().

vma_merge() also had an unnecessary call to vma_iter_free() since the
logic change to abort earlier if no merging is necessary.

Drop extra validate_mm() calls at the start of functions and error paths
which won't write to the tree.

Relocate the validate_mm() call in the do_brk_flags() to avoid
re-running the same test when vma_complete() is used.

The call within the error path of mmap_region() is left intentionally
because of the complexity of the function and the potential of drivers
modifying the tree.

Link: https://lkml.kernel.org/r/20230714195551.894800-1-Liam.Howlett@oracle.com
Link: https://lkml.kernel.org/r/20230714195551.894800-2-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oliver Sang <oliver.sang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

show more ...

mm/mmap: move vma operations to mm_struct out of the critical section of file mapping lock

UnixBench/Execl represents a class of workload where bash scripts are
spawned frequently to do some short j

mm/mmap: move vma operations to mm_struct out of the critical section of file mapping lock

UnixBench/Execl represents a class of workload where bash scripts are
spawned frequently to do some short jobs. When running multiple parallel
tasks, hot osq_lock is observed from do_mmap and exit_mmap. Both of them
come from load_elf_binary through the call chain
"execl->do_execveat_common->bprm_execve->load_elf_binary".

In do_mmap,it will call mmap_region to create vma node, initialize it and
insert it to vma maintain structure in mm_struct and i_mmap tree of the
mapping file, then increase map_count to record the number of vma nodes
used. The hot osq_lock is to protect operations on file's i_mmap tree.
For the mm_struct member change like vma insertion and map_count update,
they do not affect i_mmap tree. Move those operations out of the lock's
critical section, to reduce hold time on the lock.

With this change, on Intel Sapphire Rapids 112C/224T platform, based on
v6.0-rc6, the 160 parallel score improves by 12%. The patch has no
obvious performance gain on v6.5-rc1 due to regression of this benchmark
from this commit f1a7941243c102a44e8847e3b94ff4ff3ec56f25 (mm: convert
mm's rss stats into percpu_counter). Related discussion and conclusion
can be referred at the mail thread initiated by 0day as below: Link:
https://lore.kernel.org/linux-mm/a4aa2e13-7187-600b-c628-7e8fb108def0@intel.com/

Link: https://lkml.kernel.org/r/20230712145739.604215-1-yu.ma@intel.com
Signed-off-by: Yu Ma <yu.ma@intel.com>
Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Kirill A . Shutemov <kirill@shutemov.name>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Zhu, Lipeng <lipeng.zhu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

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mm: lock VMA in dup_anon_vma() before setting ->anon_vma

When VMAs are merged, dup_anon_vma() is called with `dst` pointing to the
VMA that is being expanded to cover the area previously occupied by

mm: lock VMA in dup_anon_vma() before setting ->anon_vma

When VMAs are merged, dup_anon_vma() is called with `dst` pointing to the
VMA that is being expanded to cover the area previously occupied by
another VMA. This currently happens while `dst` is not write-locked.

This means that, in the `src->anon_vma && !dst->anon_vma` case, as soon as
the assignment `dst->anon_vma = src->anon_vma` has happened, concurrent
page faults can happen on `dst` under the per-VMA lock. This is already
icky in itself, since such page faults can now install pages into `dst`
that are attached to an `anon_vma` that is not yet tied back to the
`anon_vma` with an `anon_vma_chain`. But if `anon_vma_clone()` fails due
to an out-of-memory error, things get much worse: `anon_vma_clone()` then
reverts `dst->anon_vma` back to NULL, and `dst` remains completely
unconnected to the `anon_vma`, even though we can have pages in the area
covered by `dst` that point to the `anon_vma`.

This means the `anon_vma` of such pages can be freed while the pages are
still mapped into userspace, which leads to UAF when a helper like
folio_lock_anon_vma_read() tries to look up the anon_vma of such a page.

This theoretically is a security bug, but I believe it is really hard to
actually trigger as an unprivileged user because it requires that you can
make an order-0 GFP_KERNEL allocation fail, and the page allocator tries
pretty hard to prevent that.

I think doing the vma_start_write() call inside dup_anon_vma() is the most
straightforward fix for now.

For a kernel-assisted reproducer, see the notes section of the patch mail.

Link: https://lkml.kernel.org/r/20230721034643.616851-1-jannh@google.com
Fixes: 5e31275cc997 ("mm: add per-VMA lock and helper functions to control it")
Signed-off-by: Jann Horn <jannh@google.com>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

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mm: Add guard pages around a shadow stack.

The x86 Control-flow Enforcement Technology (CET) feature includes a new
type of memory called shadow stack. This shadow stack memory has some
unusual prop

mm: Add guard pages around a shadow stack.

The x86 Control-flow Enforcement Technology (CET) feature includes a new
type of memory called shadow stack. This shadow stack memory has some
unusual properties, which requires some core mm changes to function
properly.

The architecture of shadow stack constrains the ability of userspace to
move the shadow stack pointer (SSP) in order to prevent corrupting or
switching to other shadow stacks. The RSTORSSP instruction can move the
SSP to different shadow stacks, but it requires a specially placed token
in order to do this. However, the architecture does not prevent
incrementing the stack pointer to wander onto an adjacent shadow stack. To
prevent this in software, enforce guard pages at the beginning of shadow
stack VMAs, such that there will always be a gap between adjacent shadow
stacks.

Make the gap big enough so that no userspace SSP changing operations
(besides RSTORSSP), can move the SSP from one stack to the next. The
SSP can be incremented or decremented by CALL, RET and INCSSP. CALL and
RET can move the SSP by a maximum of 8 bytes, at which point the shadow
stack would be accessed.

The INCSSP instruction can also increment the shadow stack pointer. It
is the shadow stack analog of an instruction like:

addq $0x80, %rsp

However, there is one important difference between an ADD on %rsp and
INCSSP. In addition to modifying SSP, INCSSP also reads from the memory
of the first and last elements that were "popped". It can be thought of
as acting like this:

READ_ONCE(ssp); // read+discard top element on stack
ssp += nr_to_pop * 8; // move the shadow stack
READ_ONCE(ssp-8); // read+discard last popped stack element

The maximum distance INCSSP can move the SSP is 2040 bytes, before it
would read the memory. Therefore, a single page gap will be enough to
prevent any operation from shifting the SSP to an adjacent stack, since
it would have to land in the gap at least once, causing a fault.

This could be accomplished by using VM_GROWSDOWN, but this has a
downside. The behavior would allow shadow stacks to grow, which is
unneeded and adds a strange difference to how most regular stacks work.

In the maple tree code, there is some logic for retrying the unmapped
area search if a guard gap is violated. This retry should happen for
shadow stack guard gap violations as well. This logic currently only
checks for VM_GROWSDOWN for start gaps. Since shadow stacks also have
a start gap as well, create an new define VM_STARTGAP_FLAGS to hold
all the VM flag bits that have start gaps, and make mmap use it.

Co-developed-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/all/20230613001108.3040476-17-rick.p.edgecombe%40intel.com

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mm: Re-introduce vm_flags to do_mmap()

There was no more caller passing vm_flags to do_mmap(), and vm_flags was
removed from the function's input by:

commit 45e55300f114 ("mm: remove unnecessar

mm: Re-introduce vm_flags to do_mmap()

There was no more caller passing vm_flags to do_mmap(), and vm_flags was
removed from the function's input by:

commit 45e55300f114 ("mm: remove unnecessary wrapper function do_mmap_pgoff()").

There is a new user now. Shadow stack allocation passes VM_SHADOW_STACK to
do_mmap(). Thus, re-introduce vm_flags to do_mmap().

Co-developed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Peter Collingbourne <pcc@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
Acked-by: David Hildenbrand <david@redhat.com>
Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Kees Cook <keescook@chromium.org>
Tested-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/all/20230613001108.3040476-5-rick.p.edgecombe%40intel.com

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mm: lock newly mapped VMA with corrected ordering

Lockdep is certainly right to complain about

(&vma->vm_lock->lock){++++}-{3:3}, at: vma_start_write+0x2d/0x3f
but task is alread

mm: lock newly mapped VMA with corrected ordering

Lockdep is certainly right to complain about

(&vma->vm_lock->lock){++++}-{3:3}, at: vma_start_write+0x2d/0x3f
but task is already holding lock:
(&mapping->i_mmap_rwsem){+.+.}-{3:3}, at: mmap_region+0x4dc/0x6db

Invert those to the usual ordering.

Fixes: 33313a747e81 ("mm: lock newly mapped VMA which can be modified after it becomes visible")
Cc: stable@vger.kernel.org
Signed-off-by: Hugh Dickins <hughd@google.com>
Tested-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

show more ...

mm: lock newly mapped VMA which can be modified after it becomes visible

mmap_region adds a newly created VMA into VMA tree and might modify it
afterwards before dropping the mmap_lock. This poses

mm: lock newly mapped VMA which can be modified after it becomes visible

mmap_region adds a newly created VMA into VMA tree and might modify it
afterwards before dropping the mmap_lock. This poses a problem for page
faults handled under per-VMA locks because they don't take the mmap_lock
and can stumble on this VMA while it's still being modified. Currently
this does not pose a problem since post-addition modifications are done
only for file-backed VMAs, which are not handled under per-VMA lock.
However, once support for handling file-backed page faults with per-VMA
locks is added, this will become a race.

Fix this by write-locking the VMA before inserting it into the VMA tree.
Other places where a new VMA is added into VMA tree do not modify it
after the insertion, so do not need the same locking.

Cc: stable@vger.kernel.org
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

show more ...

mm: lock a vma before stack expansion

With recent changes necessitating mmap_lock to be held for write while
expanding a stack, per-VMA locks should follow the same rules and be
write-locked to prev

mm: lock a vma before stack expansion

With recent changes necessitating mmap_lock to be held for write while
expanding a stack, per-VMA locks should follow the same rules and be
write-locked to prevent page faults into the VMA being expanded. Add
the necessary locking.

Cc: stable@vger.kernel.org
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

show more ...