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SubjectRe: [PATCH v3] vmw_balloon: fixing double free when batching mode is off
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Nadav Amit <namit@vmware.com> wrote:

> Ping. Please consider it for inclusion for rc4.
>
> Nadav Amit <namit@vmware.com> wrote:
>
>> From: Gil Kupfer <gilkup@gmail.com>
>>
>> The balloon.page field is used for two different purposes if batching is
>> on or off. If batching is on, the field point to the page which is used
>> to communicate with with the hypervisor. If it is off, balloon.page
>> points to the page that is about to be (un)locked.
>>
>> Unfortunately, this dual-purpose of the field introduced a bug: when the
>> balloon is popped (e.g., when the machine is reset or the balloon driver
>> is explicitly removed), the balloon driver frees, unconditionally, the
>> page that is held in balloon.page. As a result, if batching is
>> disabled, this leads to double freeing the last page that is sent to the
>> hypervisor.
>>
>> The following error occurs during rmmod when kernel checkers are on, and
>> the balloon is not empty:
>>
>> [ 42.307653] ------------[ cut here ]------------
>> [ 42.307657] Kernel BUG at ffffffffba1e4b28 [verbose debug info unavailable]
>> [ 42.307720] invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC
>> [ 42.312512] Modules linked in: vmw_vsock_vmci_transport vsock ppdev joydev vmw_balloon(-) input_leds serio_raw vmw_vmci parport_pc shpchp parport i2c_piix4 nfit mac_hid autofs4 vmwgfx drm_kms_helper hid_generic syscopyarea sysfillrect usbhid sysimgblt fb_sys_fops hid ttm mptspi scsi_transport_spi ahci mptscsih drm psmouse vmxnet3 libahci mptbase pata_acpi
>> [ 42.312766] CPU: 10 PID: 1527 Comm: rmmod Not tainted 4.12.0+ #5
>> [ 42.312803] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 09/30/2016
>> [ 42.313042] task: ffff9bf9680f8000 task.stack: ffffbfefc1638000
>> [ 42.313290] RIP: 0010:__free_pages+0x38/0x40
>> [ 42.313510] RSP: 0018:ffffbfefc163be98 EFLAGS: 00010246
>> [ 42.313731] RAX: 000000000000003e RBX: ffffffffc02b9720 RCX: 0000000000000006
>> [ 42.313972] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff9bf97e08e0a0
>> [ 42.314201] RBP: ffffbfefc163be98 R08: 0000000000000000 R09: 0000000000000000
>> [ 42.314435] R10: 0000000000000000 R11: 0000000000000000 R12: ffffffffc02b97e4
>> [ 42.314505] R13: ffffffffc02b9748 R14: ffffffffc02b9728 R15: 0000000000000200
>> [ 42.314550] FS: 00007f3af5fec700(0000) GS:ffff9bf97e080000(0000) knlGS:0000000000000000
>> [ 42.314599] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> [ 42.314635] CR2: 00007f44f6f4ab24 CR3: 00000003a7d12000 CR4: 00000000000006e0
>> [ 42.314864] Call Trace:
>> [ 42.315774] vmballoon_pop+0x102/0x130 [vmw_balloon]
>> [ 42.315816] vmballoon_exit+0x42/0xd64 [vmw_balloon]
>> [ 42.315853] SyS_delete_module+0x1e2/0x250
>> [ 42.315891] entry_SYSCALL_64_fastpath+0x23/0xc2
>> [ 42.315924] RIP: 0033:0x7f3af5b0e8e7
>> [ 42.315949] RSP: 002b:00007fffe6ce0148 EFLAGS: 00000206 ORIG_RAX: 00000000000000b0
>> [ 42.315996] RAX: ffffffffffffffda RBX: 000055be676401e0 RCX: 00007f3af5b0e8e7
>> [ 42.316951] RDX: 000000000000000a RSI: 0000000000000800 RDI: 000055be67640248
>> [ 42.317887] RBP: 0000000000000003 R08: 0000000000000000 R09: 1999999999999999
>> [ 42.318845] R10: 0000000000000883 R11: 0000000000000206 R12: 00007fffe6cdf130
>> [ 42.319755] R13: 0000000000000000 R14: 0000000000000000 R15: 000055be676401e0
>> [ 42.320606] Code: c0 74 1c f0 ff 4f 1c 74 02 5d c3 85 f6 74 07 e8 0f d8 ff ff 5d c3 31 f6 e8 c6 fb ff ff 5d c3 48 c7 c6 c8 0f c5 ba e8 58 be 02 00 <0f> 0b 66 0f 1f 44 00 00 66 66 66 66 90 48 85 ff 75 01 c3 55 48
>> [ 42.323462] RIP: __free_pages+0x38/0x40 RSP: ffffbfefc163be98
>> [ 42.325735] ---[ end trace 872e008e33f81508 ]---
>>
>> To solve the bug, we eliminate the dual purpose of balloon.page.
>>
>> Fixes: f220a80f0c2e ("VMware balloon: add batching to the vmw_balloon.")
>> Cc: stable@vger.kernel.org
>> Reported-by: Oleksandr Natalenko <onatalen@redhat.com>
>> Signed-off-by: Gil Kupfer <gilkup@gmail.com>
>> Signed-off-by: Nadav Amit <namit@vmware.com>
>> Reviewed-by: Xavier Deguillard <xdeguillard@vmware.com>
>> ---
>> drivers/misc/vmw_balloon.c | 23 +++++++----------------
>> 1 file changed, 7 insertions(+), 16 deletions(-)
>>
>> diff --git a/drivers/misc/vmw_balloon.c b/drivers/misc/vmw_balloon.c
>> index 9047c0a529b2..efd733472a35 100644
>> --- a/drivers/misc/vmw_balloon.c
>> +++ b/drivers/misc/vmw_balloon.c
>> @@ -576,15 +576,9 @@ static void vmballoon_pop(struct vmballoon *b)
>> }
>> }
>>
>> - if (b->batch_page) {
>> - vunmap(b->batch_page);
>> - b->batch_page = NULL;
>> - }
>> -
>> - if (b->page) {
>> - __free_page(b->page);
>> - b->page = NULL;
>> - }
>> + /* Clearing the batch_page unconditionally has no adverse effect */
>> + free_page((unsigned long)b->batch_page);
>> + b->batch_page = NULL;
>> }
>>
>> /*
>> @@ -991,16 +985,13 @@ static const struct vmballoon_ops vmballoon_batched_ops = {
>>
>> static bool vmballoon_init_batching(struct vmballoon *b)
>> {
>> - b->page = alloc_page(VMW_PAGE_ALLOC_NOSLEEP);
>> - if (!b->page)
>> - return false;
>> + struct page *page;
>>
>> - b->batch_page = vmap(&b->page, 1, VM_MAP, PAGE_KERNEL);
>> - if (!b->batch_page) {
>> - __free_page(b->page);
>> + page = alloc_page(GFP_KERNEL | __GFP_ZERO);
>> + if (!page)
>> return false;
>> - }
>>
>> + b->batch_page = page_address(page);
>> return true;
>> }
>>
>> --
>> 2.14.1

Greg, can you please include this patch?? 4.17 is almost out of the door,
and the last version was sent a month ago.

If you have any reservations, please let me know immediately.

Regards,
Nadav
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