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

Uladzislau Rezki
2024-07-24T19:27:50Z

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.