Re: [PATCH] arm64: kasan: fix phys_to_virt() false positive on tag-based kasan

[Mark Rutland]

On Mon, Aug 19, 2019 at 01:56:26PM +0100, Will Deacon wrote:
> On Mon, Aug 19, 2019 at 07:44:20PM +0800, Walter Wu wrote:
> > __arm_v7s_unmap() call iopte_deref() to translate pyh_to_virt address,
> > but it will modify pointer tag into 0xff, so there is a false positive.
> > 
> > When enable tag-based kasan, phys_to_virt() function need to rewrite
> > its original pointer tag in order to avoid kasan report an incorrect
> > memory corruption.
> 
> Hmm. Which tree did you see this on? We've recently queued a load of fixes
> in this area, but I /thought/ they were only needed after the support for
> 52-bit virtual addressing in the kernel.

I'm seeing similar issues in the virtio blk code (splat below), atop of
the arm64 for-next/core branch. I think this is a latent issue, and
people are only just starting to test with KASAN_SW_TAGS.

It looks like the virtio blk code will round-trip a SLUB-allocated pointer from
virt->page->virt, losing the per-object tag in the process.

Our page_to_virt() seems to get a per-page tag, but this only makes
sense if you're dealing with the page allocator, rather than something
like SLUB which carves a page into smaller objects giving each object a
distinct tag.

Any round-trip of a pointer from SLUB is going to lose the per-object
tag.

Thanks,
Mark.

==================================================================
BUG: KASAN: double-free or invalid-free in virtblk_request_done+0x128/0x1d8 drivers/block/virtio_blk.c:215
Pointer tag: [ff], memory tag: [a8]

CPU: 0 PID: 19116 Comm: syz-executor.0 Not tainted 5.3.0-rc3-00075-gcb38552 #1
Hardware name: linux,dummy-virt (DT)
Call trace:
 dump_backtrace+0x0/0x3c0 arch/arm64/include/asm/stacktrace.h:166
 show_stack+0x24/0x30 arch/arm64/kernel/traps.c:138
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x138/0x1f4 lib/dump_stack.c:113
 print_address_description+0x7c/0x328 mm/kasan/report.c:351
 kasan_report_invalid_free+0x80/0xe0 mm/kasan/report.c:444
 __kasan_slab_free+0x1a8/0x208 mm/kasan/common.c:56
 kasan_slab_free+0xc/0x18 mm/kasan/common.c:457
 slab_free_hook mm/slub.c:1423 [inline]
 slab_free_freelist_hook mm/slub.c:1474 [inline]
 slab_free mm/slub.c:3016 [inline]
 kfree+0x254/0x9dc mm/slub.c:3957
 virtblk_request_done+0x128/0x1d8 drivers/block/virtio_blk.c:215
 blk_done_softirq+0x3dc/0x49c block/blk-softirq.c:37
 __do_softirq+0xa90/0x1504 kernel/softirq.c:292
 do_softirq_own_stack include/linux/interrupt.h:549 [inline]
 invoke_softirq kernel/softirq.c:380 [inline]
 irq_exit+0x3b0/0x4f8 kernel/softirq.c:413
 __handle_domain_irq+0x150/0x250 kernel/irq/irqdesc.c:671
 atomic_read include/asm-generic/atomic-instrumented.h:26 [inline]
 static_key_count include/linux/jump_label.h:254 [inline]
 cpus_have_const_cap arch/arm64/include/asm/cpufeature.h:410 [inline]
 gic_read_iar drivers/irqchip/irq-gic-v3.c:152 [inline]
 gic_handle_irq+0x244/0x4ac drivers/irqchip/irq-gic-v3.c:490
 el1_irq+0xbc/0x140 arch/arm64/kernel/entry.S:670
 ktime_add_safe kernel/time/hrtimer.c:321 [inline]
 hrtimer_set_expires_range_ns include/linux/hrtimer.h:235 [inline]
 hrtimer_nanosleep kernel/time/hrtimer.c:1732 [inline]
 __do_sys_nanosleep kernel/time/hrtimer.c:1767 [inline]
 __se_sys_nanosleep kernel/time/hrtimer.c:1754 [inline]
 __arm64_sys_nanosleep+0x344/0x554 kernel/time/hrtimer.c:1754
 __invoke_syscall arch/arm64/kernel/syscall.c:36 [inline]
 invoke_syscall arch/arm64/kernel/syscall.c:48 [inline]
 el0_svc_common arch/arm64/kernel/syscall.c:114 [inline]
 el0_svc_handler+0x300/0x540 arch/arm64/kernel/syscall.c:160
 el0_svc+0x8/0xc arch/arm64/kernel/entry.S:1006

Allocated by task 170:
 save_stack mm/kasan/common.c:69 [inline]
 set_track mm/kasan/common.c:77 [inline]
 __kasan_kmalloc+0x114/0x1d0 mm/kasan/common.c:487
 kasan_kmalloc+0x10/0x18 mm/kasan/common.c:501
 __kmalloc+0x1f0/0x48c mm/slub.c:3811
 kmalloc_array include/linux/slab.h:676 [inline]
 virtblk_setup_discard_write_zeroes drivers/block/virtio_blk.c:188 [inline]
 virtio_queue_rq+0x948/0xe48 drivers/block/virtio_blk.c:322
 blk_mq_dispatch_rq_list+0x914/0x16fc block/blk-mq.c:1257
 blk_mq_do_dispatch_sched+0x374/0x4d8 block/blk-mq-sched.c:115
 blk_mq_sched_dispatch_requests+0x4d0/0x68c block/blk-mq-sched.c:216
 __blk_mq_run_hw_queue+0x22c/0x35c block/blk-mq.c:1387
 blk_mq_run_work_fn+0x64/0x78 block/blk-mq.c:1620
 process_one_work+0x10bc/0x1df0 kernel/workqueue.c:2269
 worker_thread+0x1124/0x17bc kernel/workqueue.c:2415
 kthread+0x3c0/0x3d0 kernel/kthread.c:255
 ret_from_fork+0x10/0x18 arch/arm64/kernel/entry.S:1164

Freed by task 17121:
 save_stack mm/kasan/common.c:69 [inline]
 set_track mm/kasan/common.c:77 [inline]
 __kasan_slab_free+0x138/0x208 mm/kasan/common.c:449
 kasan_slab_free+0xc/0x18 mm/kasan/common.c:457
 slab_free_hook mm/slub.c:1423 [inline]
 slab_free_freelist_hook mm/slub.c:1474 [inline]
 slab_free mm/slub.c:3016 [inline]
 kfree+0x254/0x9dc mm/slub.c:3957
 kvfree+0x54/0x60 mm/util.c:488
 __vunmap+0xa3c/0xafc mm/vmalloc.c:2255
 __vfree mm/vmalloc.c:2299 [inline]
 vfree+0xe4/0x1c4 mm/vmalloc.c:2329
 copy_entries_to_user net/ipv6/netfilter/ip6_tables.c:883 [inline]
 get_entries net/ipv6/netfilter/ip6_tables.c:1041 [inline]
 do_ip6t_get_ctl+0xf78/0x1804 net/ipv6/netfilter/ip6_tables.c:1709
 nf_sockopt net/netfilter/nf_sockopt.c:104 [inline]
 nf_getsockopt+0x238/0x258 net/netfilter/nf_sockopt.c:122
 ipv6_getsockopt+0x3374/0x40c4 net/ipv6/ipv6_sockglue.c:1400
 tcp_getsockopt+0x214/0x54e0 net/ipv4/tcp.c:3662
 sock_common_getsockopt+0xc8/0xf4 net/core/sock.c:3089
 __sys_getsockopt net/socket.c:2129 [inline]
 __do_sys_getsockopt net/socket.c:2144 [inline]
 __se_sys_getsockopt net/socket.c:2141 [inline]
 __arm64_sys_getsockopt+0x240/0x308 net/socket.c:2141
 __invoke_syscall arch/arm64/kernel/syscall.c:36 [inline]
 invoke_syscall arch/arm64/kernel/syscall.c:48 [inline]
 el0_svc_common arch/arm64/kernel/syscall.c:114 [inline]
 el0_svc_handler+0x300/0x540 arch/arm64/kernel/syscall.c:160
 el0_svc+0x8/0xc arch/arm64/kernel/entry.S:1006

The buggy address belongs to the object at ffff00005338eb80
 which belongs to the cache kmalloc-128 of size 128
The buggy address is located 0 bytes inside of
 128-byte region [ffff00005338eb80, ffff00005338ec00)
The buggy address belongs to the page:
page:ffffffdffff4ce00 refcount:1 mapcount:0 mapping:e5ff0000576b0480 index:0x29ff000053388f00
flags: 0xffffff000000200(slab)
raw: 0ffffff000000200 ffffffdffff00108 5eff0000576afd40 e5ff0000576b0480
raw: 29ff000053388f00 000000000066005d 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff00005338e900: 34 34 34 34 34 34 34 34 fe fe fe fe fe fe fe fe
 ffff00005338ea00: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
>ffff00005338eb00: fe fe fe fe fe fe fe fe a8 fe fe fe fe fe fe fe
                                           ^
 ffff00005338ec00: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
 ffff00005338ed00: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
==================================================================