Re: [PATCH] mm: fix racing of vb->va when kasan enabled

From: Uladzislau Rezki
Date: Fri Jun 24 2022 - 06:51:37 EST

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In reply to: Uladzislau Rezki: "Re: [PATCH] mm: fix racing of vb->va when kasan enabled"
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> > On Wed, Jun 22, 2022 at 11:15 AM Zhaoyang Huang <huangzhaoyang@xxxxxxxxx> wrote:
> > >
> > > On Tue, Jun 21, 2022 at 10:29 PM Uladzislau Rezki <urezki@xxxxxxxxx> wrote:
> > > >
> > > > > On Tue, Jun 21, 2022 at 5:27 PM Uladzislau Rezki <urezki@xxxxxxxxx> wrote:
> > > > > >
> > > > > > > On Mon, Jun 20, 2022 at 6:44 PM Uladzislau Rezki <urezki@xxxxxxxxx> wrote:
> > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > Is it easy to reproduce? If so could you please describe the steps? As i see
> > > > > > > > > > the freeing of the "vb" is RCU safe whereas vb->va is not. But from the first
> > > > > > > > > > glance i do not see how it can accessed twice. Hm..
> > > > > > > > > It was raised from a monkey test on A13_k515 system and got 1/20 pcs
> > > > > > > > > failed. IMO, vb->va which out of vmap_purge_lock protection could race
> > > > > > > > > with a concurrent ra freeing within __purge_vmap_area_lazy.
> > > > > > > > >
> > > > > > > > Do you have exact steps how you run "monkey" test?
> > > > > > > There are about 30+ kos inserted during startup which could be a
> > > > > > > specific criteria for reproduction. Do you have doubts about the test
> > > > > > > result or the solution?
> > > > > > > >
> > > > > > I do not have any doubt about your test results, so if you can trigger it
> > > > > > then there is an issue at least on the 5.4.161-android12 kernel.
> > > > > >
> > > > > > 1. With your fix we get expanded mutex range, thus the worst case of vmalloc
> > > > > > allocation can be increased when it fails and repeat. Because it also invokes
> > > > > > the purge_vmap_area_lazy() that access the same mutex.
> > > > > I am not sure I get your point. _vm_unmap_aliases calls
> > > > > _purge_vmap_area_lazy instead of purge_vmap_area_lazy. Do you have any
> > > > > other solutions? I really don't think my patch is the best way as I
> > > > > don't have a full view of vmalloc mechanism.
> > > > >
> > > > Yep, but it holds the mutex:
> > I still don't get how _purge_vmap_area_lazy hold vmap_purge_lock?
> >
> The user has to take the mutex if it invokes the __purge_vmap_area_lazy()
> function.
>
> > > >
> > > > <snip>
> > > > mutex_lock(&vmap_purge_lock);
> > > > purge_fragmented_blocks_allcpus();
> > > > if (!__purge_vmap_area_lazy(start, end) && flush)
> > > > flush_tlb_kernel_range(start, end);
> > > > mutex_unlock(&vmap_purge_lock);
> > > > <snip>
> > > >
> > > > I do not have a solution yet. I am trying still to figure out how you can
> > > > trigger it.
> > > >
> > > > <snip>
> > > > rcu_read_lock();
> > > > list_for_each_entry_rcu(vb, &vbq->free, free_list) {
> > > > spin_lock(&vb->lock);
> > > > if (vb->dirty && vb->dirty != VMAP_BBMAP_BITS) {
> > > > unsigned long va_start = vb->va->va_start;
> > > > <snip>
> > > >
> > > > so you say that "vb->va->va_start" can be accessed twice. I do not see
> > > > how it can happen. The purge_fragmented_blocks() removes "vb" from the
> > > > free_list and set vb->dirty to the VMAP_BBMAP_BITS to prevent purging
> > > > it again. It is protected by the spin_lock(&vb->lock):
> > > >
> > > > <snip>
> > > > spin_lock(&vb->lock);
> > > > if (vb->free + vb->dirty == VMAP_BBMAP_BITS && vb->dirty != VMAP_BBMAP_BITS) {
> > > > vb->free = 0; /* prevent further allocs after releasing lock */
> > > > vb->dirty = VMAP_BBMAP_BITS; /* prevent purging it again */
> > > > vb->dirty_min = 0;
> > > > vb->dirty_max = VMAP_BBMAP_BITS;
> > > > <snip>
> > > >
> > > > so the VMAP_BBMAP_BITS is set under spinlock. The _vm_unmap_aliases() checks it:
> > > >
> > > > <snip>
> > > > list_for_each_entry_rcu(vb, &vbq->free, free_list) {
> > > > spin_lock(&vb->lock);
> > > > if (vb->dirty && vb->dirty != VMAP_BBMAP_BITS) {
> > > > unsigned long va_start = vb->va->va_start;
> > > > unsigned long s, e;
> > > > <snip>
> > > >
> > > > if the "vb->dirty != VMAP_BBMAP_BITS". I am missing your point here?
> > > Could the racing be like bellowing scenario? vb->va accessed in [2]
> > > has been freed in [1]
> > >
> > > _vm_unmap_aliases
> > > _vm_unmap_aliases
> > > {
> > > {
> > > list_for_each_entry_rcu(vb, &vbq->free, free_list) {
> > > __purge_vmap_area_lazy
> > > spin_lock(&vb->lock);
> > > merge_or_add_vmap_area
> > > if (vb->dirty) {
> > >
> > > kmem_cache_free(vmap_area_cachep, va)[1]
> > > unsigned long va_start = vb->va->va_start;
> > > [2]
> >
> > reformat the racing graph
> > _vm_unmap_aliases
> > _vm_unmap_aliases
> > {
> > {
> > list_for_each_entry_rcu(vb, &vbq->free, free_list) {
> > __purge_vmap_area_lazy
> > spin_lock(&vb->lock);
> > merge_or_add_vmap_area
> > if (vb->dirty) {
> >
> > kmem_cache_free(vmap_area_cachep, va)[1]
> > unsigned long va_start = vb->va->va_start; [2]
> >
> > > >
> > > > > >
> > > > > > 2. You run 5.4.161-android12 kernel what is quite old. Could you please
> > > > > > retest with latest kernel? I am asking because on the latest kernel with
> > > > > > CONFIG_KASAN i am not able to reproduce it.
> > > > > >
> > > > > > I do a lot of: vm_map_ram()/vm_unmap_ram()/vmalloc()/vfree() in parallel
> > > > > > by 64 kthreads on my 64 CPUs test system.
> > > > > The failure generates at 20s from starting up, I think it is a rare timing.
> > > > > >
> > > > > > Could you please confirm that you can trigger an issue on the latest kernel?
> > > > > Sorry, I don't have an available latest kernel for now.
> > > > >
> > > > Can you do: "gdb ./vmlinux", execute "l *_vm_unmap_aliases+0x164" and provide
> > > > output?
> > Sorry, I have lost the vmlinux with KASAN enabled and just got some
> > instructions from logs.
> >
> > 0xffffffd010678da8 <_vm_unmap_aliases+0x134>: sub x22, x26, #0x28
> > x26 vbq->free
> > 0xffffffd010678dac <_vm_unmap_aliases+0x138>: lsr x8, x22, #3
> > 0xffffffd010678db0 <_vm_unmap_aliases+0x13c>: ldrb w8, [x8,x24]
> > 0xffffffd010678db4 <_vm_unmap_aliases+0x140>: cbz w8,
> > 0xffffffd010678dc0 <_vm_unmap_aliases+0x14c>
> > 0xffffffd010678db8 <_vm_unmap_aliases+0x144>: mov x0, x22
> > 0xffffffd010678dbc <_vm_unmap_aliases+0x148>: bl 0xffffffd0106c9a34
> > <__asan_report_load8_noabort>
> > 0xffffffd010678dc0 <_vm_unmap_aliases+0x14c>: ldr x22, [x22]
> > 0xffffffd010678dc4 <_vm_unmap_aliases+0x150>: lsr x8, x22, #3
> > 0xffffffd010678dc8 <_vm_unmap_aliases+0x154>: ldrb w8, [x8,x24]
> > 0xffffffd010678dcc <_vm_unmap_aliases+0x158>: cbz w8,
> > 0xffffffd010678dd8 <_vm_unmap_aliases+0x164>
> > 0xffffffd010678dd0 <_vm_unmap_aliases+0x15c>: mov x0, x22
> > 0xffffffd010678dd4 <_vm_unmap_aliases+0x160>: bl 0xffffffd0106c9a34
> > <__asan_report_load8_noabort>
> >
> Could you please test below patch if that fixes an issue on the 5.4
> kernel:
>
> <snip>
> diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> index 4e7809408073..d5b07d7239bd 100644
> --- a/include/linux/vmalloc.h
> +++ b/include/linux/vmalloc.h
> @@ -55,6 +55,7 @@ struct vmap_area {
>
> struct rb_node rb_node; /* address sorted rbtree */
> struct list_head list; /* address sorted list */
> + struct rcu_head rcu;
>
> /*
> * The following three variables can be packed, because
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index a3c70e275f4e..bb8cfdb06ce6 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -337,14 +337,6 @@ static LLIST_HEAD(vmap_purge_list);
> static struct rb_root vmap_area_root = RB_ROOT;
> static bool vmap_initialized __read_mostly;
>
> -/*
> - * This kmem_cache is used for vmap_area objects. Instead of
> - * allocating from slab we reuse an object from this cache to
> - * make things faster. Especially in "no edge" splitting of
> - * free block.
> - */
> -static struct kmem_cache *vmap_area_cachep;
> -
> /*
> * This linked list is used in pair with free_vmap_area_root.
> * It gives O(1) access to prev/next to perform fast coalescing.
> @@ -532,7 +524,7 @@ link_va(struct vmap_area *va, struct rb_root *root,
> }
>
> /* Address-sort this list */
> - list_add(&va->list, head);
> + list_add_rcu(&va->list, head);
> }
>
> static __always_inline void
> @@ -547,7 +539,7 @@ unlink_va(struct vmap_area *va, struct rb_root *root)
> else
> rb_erase(&va->rb_node, root);
>
> - list_del(&va->list);
> + list_del_rcu(&va->list);
> RB_CLEAR_NODE(&va->rb_node);
> }
>
> @@ -721,7 +713,7 @@ merge_or_add_vmap_area(struct vmap_area *va,
> augment_tree_propagate_from(sibling);
>
> /* Free vmap_area object. */
> - kmem_cache_free(vmap_area_cachep, va);
> + kfree_rcu(va, rcu);
>
> /* Point to the new merged area. */
> va = sibling;
> @@ -748,7 +740,7 @@ merge_or_add_vmap_area(struct vmap_area *va,
> unlink_va(va, root);
>
> /* Free vmap_area object. */
> - kmem_cache_free(vmap_area_cachep, va);
> + kfree_rcu(va, rcu);
> return;
> }
> }
> @@ -928,7 +920,7 @@ adjust_va_to_fit_type(struct vmap_area *va,
> * |---------------|
> */
> unlink_va(va, &free_vmap_area_root);
> - kmem_cache_free(vmap_area_cachep, va);
> + kfree_rcu(va, rcu);
> } else if (type == LE_FIT_TYPE) {
> /*
> * Split left edge of fit VA.
> @@ -969,7 +961,7 @@ adjust_va_to_fit_type(struct vmap_area *va,
> * a first allocation (early boot up) when we have "one"
> * big free space that has to be split.
> */
> - lva = kmem_cache_alloc(vmap_area_cachep, GFP_NOWAIT);
> + lva = kmalloc(sizeof(struct vmap_area), GFP_NOWAIT);
> if (!lva)
> return -1;
> }
> @@ -1064,8 +1056,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
>
> might_sleep();
>
> - va = kmem_cache_alloc_node(vmap_area_cachep,
> - gfp_mask & GFP_RECLAIM_MASK, node);
> + va = kmalloc_node(sizeof(struct vmap_area), gfp_mask & GFP_RECLAIM_MASK, node);
> if (unlikely(!va))
> return ERR_PTR(-ENOMEM);
>
> @@ -1091,12 +1082,12 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
> preempt_disable();
> if (!__this_cpu_read(ne_fit_preload_node)) {
> preempt_enable();
> - pva = kmem_cache_alloc_node(vmap_area_cachep, GFP_KERNEL, node);
> + pva = kmalloc_node(sizeof(struct vmap_area), GFP_KERNEL, node);
> preempt_disable();
>
> if (__this_cpu_cmpxchg(ne_fit_preload_node, NULL, pva)) {
> if (pva)
> - kmem_cache_free(vmap_area_cachep, pva);
> + kfree_rcu(pva, rcu);
> }
> }
>
> @@ -1145,7 +1136,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
> pr_warn("vmap allocation for size %lu failed: use vmalloc=<size> to increase size\n",
> size);
>
> - kmem_cache_free(vmap_area_cachep, va);
> + kfree_rcu(va, rcu);
> return ERR_PTR(-EBUSY);
> }
>
> @@ -1870,7 +1861,7 @@ static void vmap_init_free_space(void)
> */
> list_for_each_entry(busy, &vmap_area_list, list) {
> if (busy->va_start - vmap_start > 0) {
> - free = kmem_cache_zalloc(vmap_area_cachep, GFP_NOWAIT);
> + free = kzalloc(sizeof(struct vmap_area), GFP_NOWAIT);
> if (!WARN_ON_ONCE(!free)) {
> free->va_start = vmap_start;
> free->va_end = busy->va_start;
> @@ -1885,7 +1876,7 @@ static void vmap_init_free_space(void)
> }
>
> if (vmap_end - vmap_start > 0) {
> - free = kmem_cache_zalloc(vmap_area_cachep, GFP_NOWAIT);
> + free = kzalloc(sizeof(struct vmap_area), GFP_NOWAIT);
> if (!WARN_ON_ONCE(!free)) {
> free->va_start = vmap_start;
> free->va_end = vmap_end;
> @@ -1903,11 +1894,6 @@ void __init vmalloc_init(void)
> struct vm_struct *tmp;
> int i;
>
> - /*
> - * Create the cache for vmap_area objects.
> - */
> - vmap_area_cachep = KMEM_CACHE(vmap_area, SLAB_PANIC);
> -
> for_each_possible_cpu(i) {
> struct vmap_block_queue *vbq;
> struct vfree_deferred *p;
> @@ -1922,7 +1908,7 @@ void __init vmalloc_init(void)
>
> /* Import existing vmlist entries. */
> for (tmp = vmlist; tmp; tmp = tmp->next) {
> - va = kmem_cache_zalloc(vmap_area_cachep, GFP_NOWAIT);
> + va = kzalloc(sizeof(struct vmap_area), GFP_NOWAIT);
> if (WARN_ON_ONCE(!va))
> continue;
>
> @@ -3256,7 +3242,7 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
> goto err_free2;
>
> for (area = 0; area < nr_vms; area++) {
> - vas[area] = kmem_cache_zalloc(vmap_area_cachep, GFP_KERNEL);
> + vas[area] = kzalloc(sizeof(struct vmap_area), GFP_KERNEL);
> vms[area] = kzalloc(sizeof(struct vm_struct), GFP_KERNEL);
> if (!vas[area] || !vms[area])
> goto err_free;
> @@ -3376,8 +3362,7 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
> if (vas[area])
> continue;
>
> - vas[area] = kmem_cache_zalloc(
> - vmap_area_cachep, GFP_KERNEL);
> + vas[area] = kzalloc(sizeof(struct vmap_area), GFP_KERNEL);
> if (!vas[area])
> goto err_free;
> }
> @@ -3388,7 +3373,7 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
> err_free:
> for (area = 0; area < nr_vms; area++) {
> if (vas[area])
> - kmem_cache_free(vmap_area_cachep, vas[area]);
> + kfree_rcu(vas[area], rcu);
>
> kfree(vms[area]);
> }
> <snip>
>
>
> --
> Uladzislau Rezki
>
OK. I was checking the sources of the 5.19 kernel that is why i did not
see how vb->va can be accessed twice. Indeed on the 5.4 kernel there was
a bug and it was fixed in the v5.13-rc1.

<snip>
commit ad216c0316ad6391d90f4de0a7f59396b2925a06
Author: Vijayanand Jitta <vjitta@xxxxxxxxxxxxxx>
Date: Thu Apr 29 22:59:07 2021 -0700

mm: vmalloc: prevent use after free in _vm_unmap_aliases

A potential use after free can occur in _vm_unmap_aliases where an already
freed vmap_area could be accessed, Consider the following scenario:

Process 1 Process 2

__vm_unmap_aliases __vm_unmap_aliases
purge_fragmented_blocks_allcpus rcu_read_lock()
rcu_read_lock()
list_del_rcu(&vb->free_list)
list_for_each_entry_rcu(vb .. )
__purge_vmap_area_lazy
kmem_cache_free(va)
va_start = vb->va->va_start

Here Process 1 is in purge path and it does list_del_rcu on vmap_block and
later frees the vmap_area, since Process 2 was holding the rcu lock at
this time vmap_block will still be present in and Process 2 accesse it and
thereby it tries to access vmap_area of that vmap_block which was already
freed by Process 1 and this results in use after free.

Fix this by adding a check for vb->dirty before accessing vmap_area
structure since vb->dirty will be set to VMAP_BBMAP_BITS in purge path
checking for this will prevent the use after free.

Link: https://lkml.kernel.org/r/1616062105-23263-1-git-send-email-vjitta@xxxxxxxxxxxxxx
Signed-off-by: Vijayanand Jitta <vjitta@xxxxxxxxxxxxxx>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 612a3790cfd4..51874a341ab0 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2040,7 +2040,7 @@ static void _vm_unmap_aliases(unsigned long start, unsigned long end, int flush)
rcu_read_lock();
list_for_each_entry_rcu(vb, &vbq->free, free_list) {
spin_lock(&vb->lock);
- if (vb->dirty) {
+ if (vb->dirty && vb->dirty != VMAP_BBMAP_BITS) {
unsigned long va_start = vb->va->va_start;
unsigned long s, e;
<snip>

Please apply that patch on your 5.4 kernel and then confirm if it fixes
your issue.

--
Uladzislau Rezki

Next message: Ian Abbott: "[RESEND PATCH] typecheck.h: Force a compilation error if typecheck(type,x) fails"
Previous message: patchwork-bot+netdevbpf: "Re: [Patch net-next 00/13] net: dsa: microchip: common spi probe for the ksz series switches - part 2"
In reply to: Uladzislau Rezki: "Re: [PATCH] mm: fix racing of vb->va when kasan enabled"
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