Re: [PATCH 1/1] mm/vmalloc: Add preempt point in purge_vmap_node() when enabling kasan

Uladzislau Rezki
2024-07-24T20:34:55Z

On Wed, Jul 24, 2024 at 09:27:46PM +0200, Uladzislau Rezki wrote:
> On Wed, Jul 24, 2024 at 05:09:59PM +0200, Uladzislau Rezki wrote:
> > On Wed, Jul 24, 2024 at 04:32:37PM +0200, Uladzislau Rezki wrote:
> > > On Wed, Jul 24, 2024 at 08:46:24PM +0800, Adrian Huang wrote:
> > > > > It works great and does not generate the soft-lock-up splat :)
> > > > > See below some comments:
> > > >
> > > > Great. Thanks for the confirmation.
> > > >
> > > > <snip>
> > > >
> > > > >> + kasan_release_vmalloc(start, end, start, end, KASAN_VMALLOC_TLB_FLUSH);
> > > > >> +
> > > > >>
> > > > > Do we need it here? We just did the TLB flush for en entire range in the
> > > > > __purge_vmap_area_lazy(). So, it is two times invoked and looks odd to me.
> > > > >
> > > > > Am i missing something?
> > > >
> > > > 1. The TLB flush for the entire range in __purge_vmap_area_lazy() is for
> > > > the vmalloc virtual address (VMALLOC_START->VMALLOC_END).
> > > >
> > > > 2. The TLB flush in purge_vmap_node() is for the KASAN shadow virtual address
> > > > (the shadow offset 'CONFIG_KASAN_SHADOW_OFFSET' is defined in .config).
> > > >
> > > Correct. It deals with a shadow region!
> > >
> > > >
> > > > BTW, I found my first patch has the potential risk. We need to flush TLB of
> > > > the KASAN shadow virtual address firstly. Please see the following patch for
> > > > detail. (I put the comment in the following patch). The following patch
> > > > also works well on my 256-core machine.
> > > >
> > > I noticed that and it would be my second question :)
> > >
> > > >
> > > > If you're ok with the patch, I'll submit it for upstream review. And, may I
> > > > have your tag(s): tested-by/reviewed-by? (If possible, could you please have
> > > > a test for the following patch).
> > > >
> > > I am OK. I will test and get back soon.
> > >
> > > > Thanks.
> > > >
> > > > ---
> > > > diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> > > > index 70d6a8f6e25d..ddbf42a1a7b7 100644
> > > > --- a/include/linux/kasan.h
> > > > +++ b/include/linux/kasan.h
> > > > @@ -55,6 +55,9 @@ extern p4d_t kasan_early_shadow_p4d[MAX_PTRS_PER_P4D];
> > > > int kasan_populate_early_shadow(const void *shadow_start,
> > > > const void *shadow_end);
> > > >
> > > > +#define KASAN_VMALLOC_PAGE_RANGE 0x1 /* Apply exsiting page range */
> > > > +#define KASAN_VMALLOC_TLB_FLUSH 0x2 /* TLB flush */
> > > > +
> > > > #ifndef kasan_mem_to_shadow
> > > > static inline void *kasan_mem_to_shadow(const void *addr)
> > > > {
> > > > @@ -511,7 +514,8 @@ void kasan_populate_early_vm_area_shadow(void *start, unsigned long size);
> > > > int kasan_populate_vmalloc(unsigned long addr, unsigned long size);
> > > > void kasan_release_vmalloc(unsigned long start, unsigned long end,
> > > > unsigned long free_region_start,
> > > > - unsigned long free_region_end);
> > > > + unsigned long free_region_end,
> > > > + unsigned long flags);
> > > >
> > > > #else /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
> > > >
> > > > @@ -526,7 +530,8 @@ static inline int kasan_populate_vmalloc(unsigned long start,
> > > > static inline void kasan_release_vmalloc(unsigned long start,
> > > > unsigned long end,
> > > > unsigned long free_region_start,
> > > > - unsigned long free_region_end) { }
> > > > + unsigned long free_region_end,
> > > > + unsigned long flags) { }
> > > >
> > > > #endif /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
> > > >
> > > > @@ -561,7 +566,8 @@ static inline int kasan_populate_vmalloc(unsigned long start,
> > > > static inline void kasan_release_vmalloc(unsigned long start,
> > > > unsigned long end,
> > > > unsigned long free_region_start,
> > > > - unsigned long free_region_end) { }
> > > > + unsigned long free_region_end,
> > > > + unsigned long flags) { }
> > > >
> > > > static inline void *kasan_unpoison_vmalloc(const void *start,
> > > > unsigned long size,
> > > > diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
> > > > index d6210ca48dda..88d1c9dcb507 100644
> > > > --- a/mm/kasan/shadow.c
> > > > +++ b/mm/kasan/shadow.c
> > > > @@ -489,7 +489,8 @@ static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr,
> > > > */
> > > > void kasan_release_vmalloc(unsigned long start, unsigned long end,
> > > > unsigned long free_region_start,
> > > > - unsigned long free_region_end)
> > > > + unsigned long free_region_end,
> > > > + unsigned long flags)
> > > > {
> > > > void *shadow_start, *shadow_end;
> > > > unsigned long region_start, region_end;
> > > > @@ -522,12 +523,17 @@ void kasan_release_vmalloc(unsigned long start, unsigned long end,
> > > > __memset(shadow_start, KASAN_SHADOW_INIT, shadow_end - shadow_start);
> > > > return;
> > > > }
> > > > - apply_to_existing_page_range(&init_mm,
> > > > +
> > > > +
> > > > + if (flags & KASAN_VMALLOC_PAGE_RANGE)
> > > > + apply_to_existing_page_range(&init_mm,
> > > > (unsigned long)shadow_start,
> > > > size, kasan_depopulate_vmalloc_pte,
> > > > NULL);
> > > > - flush_tlb_kernel_range((unsigned long)shadow_start,
> > > > - (unsigned long)shadow_end);
> > > > +
> > > > + if (flags & KASAN_VMALLOC_TLB_FLUSH)
> > > > + flush_tlb_kernel_range((unsigned long)shadow_start,
> > > > + (unsigned long)shadow_end);
> > > > }
> > > > }
> > > >
> > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > > > index e34ea860153f..12cdc92cdb83 100644
> > > > --- a/mm/vmalloc.c
> > > > +++ b/mm/vmalloc.c
> > > > @@ -2193,8 +2193,22 @@ static void purge_vmap_node(struct work_struct *work)
> > > > struct vmap_area *va, *n_va;
> > > > LIST_HEAD(local_list);
> > remove the space.
> > > >
> > > > + unsigned long start;
> > > > + unsigned long end;
> > > > +
> > > > vn->nr_purged = 0;
> > > >
> > > > + start = list_first_entry(&vn->purge_list, struct vmap_area, list)->va_start;
> > no need to have an extra space.
> > > > +
> > > > + end = list_last_entry(&vn->purge_list, struct vmap_area, list)->va_end;
> > > > +
> > > > + /*
> > > > + * Since node_pool_add_va() returns vmap_area(s) to its pool, the
> > > > + * returned vmap_area(s) might be grabbed immediately via node_alloc()
> > > > + * by other core. We need to flush TLB firstly.
> > > > + */
> > > > + kasan_release_vmalloc(start, end, start, end, KASAN_VMALLOC_TLB_FLUSH);
> > > > +
> > > > list_for_each_entry_safe(va, n_va, &vn->purge_list, list) {
> > > > unsigned long nr = (va->va_end - va->va_start) >> PAGE_SHIFT;
> > > > unsigned long orig_start = va->va_start;
> > > > @@ -2205,7 +2219,8 @@ static void purge_vmap_node(struct work_struct *work)
> > > >
> > > > if (is_vmalloc_or_module_addr((void *)orig_start))
> > > > kasan_release_vmalloc(orig_start, orig_end,
> > > > - va->va_start, va->va_end);
> > > > + va->va_start, va->va_end,
> > > > + KASAN_VMALLOC_PAGE_RANGE);
> > >
> > orig_start and orig_end are unnecessary now. But it can be removed by
> > an extra patch!
> >
> > > >
> > > > atomic_long_sub(nr, &vmap_lazy_nr);
> > > > vn->nr_purged++;
> > > > @@ -4726,7 +4741,8 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
> > > > &free_vmap_area_list);
> > > > if (va)
> > > > kasan_release_vmalloc(orig_start, orig_end,
> > > > - va->va_start, va->va_end);
> > > > + va->va_start, va->va_end,
> > > > + KASAN_VMALLOC_PAGE_RANGE | KASAN_VMALLOC_TLB_FLUSH);
> > > > vas[area] = NULL;
> > > > }
> > > >
> > > > @@ -4776,7 +4792,8 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
> > > > &free_vmap_area_list);
> > > > if (va)
> > > > kasan_release_vmalloc(orig_start, orig_end,
> > > > - va->va_start, va->va_end);
> > > > + va->va_start, va->va_end,
> > > > + KASAN_VMALLOC_PAGE_RANGE | KASAN_VMALLOC_TLB_FLUSH);
> > > > vas[area] = NULL;
> > > > kfree(vms[area]);
> > > > }
> > Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> > Tested-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> >
> I get: BUG: KASAN: vmalloc-out-of-bounds in long_busy_list_alloc_test+0x195/0x1c0 [test_vmalloc]
>
> [15579.900340] ==================================================================
> [15579.900412] BUG: KASAN: vmalloc-out-of-bounds in long_busy_list_alloc_test+0x195/0x1c0 [test_vmalloc]
> [15579.900459] Write of size 1 at addr ffffc901c0578000 by task vmalloc_test/2/49374
>
> [15579.900506] CPU: 199 PID: 49374 Comm: vmalloc_test/2 Kdump: loaded Not tainted 6.10.0-rc5-00019-g4236f0255ea8-dirty #3450
> [15579.900554] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> [15579.900595] Call Trace:
> [15579.900611] <TASK>
> [15579.900635] dump_stack_lvl+0x53/0x70
> [15579.900670] print_address_description.constprop.0+0x2c/0x3a0
> [15579.900701] ? long_busy_list_alloc_test+0x195/0x1c0 [test_vmalloc]
> [15579.900732] print_report+0xb9/0x2b0
> [15579.900752] ? kasan_addr_to_slab+0xd/0xb0
> [15579.900776] ? long_busy_list_alloc_test+0x195/0x1c0 [test_vmalloc]
> [15579.900806] kasan_report+0xd3/0x110
> [15579.900828] ? long_busy_list_alloc_test+0x195/0x1c0 [test_vmalloc]
> [15579.900860] long_busy_list_alloc_test+0x195/0x1c0 [test_vmalloc]
> [15579.900890] ? ktime_get+0xa1/0x170
> [15579.900910] ? __pfx_long_busy_list_alloc_test+0x10/0x10 [test_vmalloc]
> [15579.900943] test_func+0x232/0x510 [test_vmalloc]
> [15579.900970] ? __pfx_test_func+0x10/0x10 [test_vmalloc]
> [15579.900998] ? __kthread_parkme+0x82/0x140
> [15579.901022] ? __pfx_test_func+0x10/0x10 [test_vmalloc]
> [15579.901049] kthread+0x2a5/0x370
> [15579.901069] ? __pfx_kthread+0x10/0x10
> [15579.901091] ret_from_fork+0x34/0x70
> [15579.901113] ? __pfx_kthread+0x10/0x10
> [15579.901135] ret_from_fork_asm+0x1a/0x30
> [15579.901161] </TASK>
>
> [15579.901189] The buggy address belongs to the virtual mapping at
> [ffffc901c0578000, ffffc901c05dd000) created by:
> long_busy_list_alloc_test+0x8e/0x1c0 [test_vmalloc]
>
> [15579.901281] The buggy address belongs to the physical page:
> [15579.901309] page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x50611a
> [15579.901312] flags: 0x17ffffc0000000(node=0|zone=2|lastcpupid=0x1fffff)
> [15579.901317] raw: 0017ffffc0000000 0000000000000000 dead000000000122 0000000000000000
> [15579.901320] raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
> [15579.901321] page dumped because: kasan: bad access detected
>
> [15579.901335] Memory state around the buggy address:
> [15579.901359] ffffc901c0577f00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
> [15579.901391] ffffc901c0577f80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
> [15579.901423] >ffffc901c0578000: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
> [15579.901455] ^
> [15579.901474] ffffc901c0578080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
> [15579.901506] ffffc901c0578100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
> [15579.901538] ==================================================================
> [15579.902332] Disabling lock debugging due to kernel taint
>
> after applying this patch. Let me check tomorrow if it is a real BUG or
> it is a side-effect of the patch.
>
You can trigger that BUG by running a vmalloc test-squite:

sudo ./test_vmalloc.sh run_test_mask=7 nr_threads=15

Reworked a bit your patch to solve a false-positive above splat:

<snip>
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 70d6a8f6e25d..ddbf42a1a7b7 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -55,6 +55,9 @@ extern p4d_t kasan_early_shadow_p4d[MAX_PTRS_PER_P4D];
int kasan_populate_early_shadow(const void *shadow_start,
const void *shadow_end);

+#define KASAN_VMALLOC_PAGE_RANGE 0x1 /* Apply exsiting page range */
+#define KASAN_VMALLOC_TLB_FLUSH 0x2 /* TLB flush */
+
#ifndef kasan_mem_to_shadow
static inline void *kasan_mem_to_shadow(const void *addr)
{
@@ -511,7 +514,8 @@ void kasan_populate_early_vm_area_shadow(void *start, unsigned long size);
int kasan_populate_vmalloc(unsigned long addr, unsigned long size);
void kasan_release_vmalloc(unsigned long start, unsigned long end,
unsigned long free_region_start,
- unsigned long free_region_end);
+ unsigned long free_region_end,
+ unsigned long flags);

#else /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */

@@ -526,7 +530,8 @@ static inline int kasan_populate_vmalloc(unsigned long start,
static inline void kasan_release_vmalloc(unsigned long start,
unsigned long end,
unsigned long free_region_start,
- unsigned long free_region_end) { }
+ unsigned long free_region_end,
+ unsigned long flags) { }

#endif /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */

@@ -561,7 +566,8 @@ static inline int kasan_populate_vmalloc(unsigned long start,
static inline void kasan_release_vmalloc(unsigned long start,
unsigned long end,
unsigned long free_region_start,
- unsigned long free_region_end) { }
+ unsigned long free_region_end,
+ unsigned long flags) { }

static inline void *kasan_unpoison_vmalloc(const void *start,
unsigned long size,
diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
index d6210ca48dda..88d1c9dcb507 100644
--- a/mm/kasan/shadow.c
+++ b/mm/kasan/shadow.c
@@ -489,7 +489,8 @@ static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr,
*/
void kasan_release_vmalloc(unsigned long start, unsigned long end,
unsigned long free_region_start,
- unsigned long free_region_end)
+ unsigned long free_region_end,
+ unsigned long flags)
{
void *shadow_start, *shadow_end;
unsigned long region_start, region_end;
@@ -522,12 +523,17 @@ void kasan_release_vmalloc(unsigned long start, unsigned long end,
__memset(shadow_start, KASAN_SHADOW_INIT, shadow_end - shadow_start);
return;
}
- apply_to_existing_page_range(&init_mm,
+
+
+ if (flags & KASAN_VMALLOC_PAGE_RANGE)
+ apply_to_existing_page_range(&init_mm,
(unsigned long)shadow_start,
size, kasan_depopulate_vmalloc_pte,
NULL);
- flush_tlb_kernel_range((unsigned long)shadow_start,
- (unsigned long)shadow_end);
+
+ if (flags & KASAN_VMALLOC_TLB_FLUSH)
+ flush_tlb_kernel_range((unsigned long)shadow_start,
+ (unsigned long)shadow_end);
}
}

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 03b82fb8ecd3..ed5eb02de545 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2186,6 +2186,25 @@ decay_va_pool_node(struct vmap_node *vn, bool full_decay)
reclaim_list_global(&decay_list);
}

+static void
+kasan_release_vmalloc_node(struct vmap_node *vn)
+{
+ struct vmap_area *va;
+ unsigned long start, end;
+
+ start = list_first_entry(&vn->purge_list, struct vmap_area, list)->va_start;
+ end = list_last_entry(&vn->purge_list, struct vmap_area, list)->va_end;
+
+ list_for_each_entry(va, &vn->purge_list, list) {
+ if (is_vmalloc_or_module_addr((void *) va->va_start))
+ kasan_release_vmalloc(va->va_start, va->va_end,
+ va->va_start, va->va_end,
+ KASAN_VMALLOC_PAGE_RANGE);
+ }
+
+ kasan_release_vmalloc(start, end, start, end, KASAN_VMALLOC_TLB_FLUSH);
+}
+
static void purge_vmap_node(struct work_struct *work)
{
struct vmap_node *vn = container_of(work,
@@ -2193,20 +2212,17 @@ static void purge_vmap_node(struct work_struct *work)
struct vmap_area *va, *n_va;
LIST_HEAD(local_list);

+ if (kasan_enabled())
+ kasan_release_vmalloc_node(vn);
+
vn->nr_purged = 0;

list_for_each_entry_safe(va, n_va, &vn->purge_list, list) {
unsigned long nr = (va->va_end - va->va_start) >> PAGE_SHIFT;
- unsigned long orig_start = va->va_start;
- unsigned long orig_end = va->va_end;
unsigned int vn_id = decode_vn_id(va->flags);

list_del_init(&va->list);

- if (is_vmalloc_or_module_addr((void *)orig_start))
- kasan_release_vmalloc(orig_start, orig_end,
- va->va_start, va->va_end);
-
atomic_long_sub(nr, &vmap_lazy_nr);
vn->nr_purged++;

@@ -4717,7 +4733,8 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
&free_vmap_area_list);
if (va)
kasan_release_vmalloc(orig_start, orig_end,
- va->va_start, va->va_end);
+ va->va_start, va->va_end,
+ KASAN_VMALLOC_PAGE_RANGE | KASAN_VMALLOC_TLB_FLUSH);
vas[area] = NULL;
}

@@ -4767,7 +4784,8 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
&free_vmap_area_list);
if (va)
kasan_release_vmalloc(orig_start, orig_end,
- va->va_start, va->va_end);
+ va->va_start, va->va_end,
+ KASAN_VMALLOC_PAGE_RANGE | KASAN_VMALLOC_TLB_FLUSH);
vas[area] = NULL;
kfree(vms[area]);
}
<snip>