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Message-ID: <b2f45c47-37e0-c9cf-27ee-68408b2b2d4c@linux.dev>
Date: Thu, 5 Dec 2024 11:20:48 +0800
From: Hao Ge <hao.ge@...ux.dev>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: kent.overstreet@...ux.dev, akpm@...ux-foundation.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Hao Ge <gehao@...inos.cn>
Subject: Re: [PATCH v2] mm/alloc_tag: fix vm_module_tags_populate's KASAN
poisoning logic
Hi Suren
On 12/5/24 10:14, Hao Ge wrote:
> Hi Suren
>
>
> On 12/5/24 03:33, Suren Baghdasaryan wrote:
>> On Wed, Dec 4, 2024 at 7:08 AM Hao Ge <hao.ge@...ux.dev> wrote:
>>> Hi Suren
>>>
>>>
>>> Thank you for your review.
>>>
>>>
>>> On 12/4/24 22:39, Suren Baghdasaryan wrote:
>>>> On Wed, Dec 4, 2024 at 12:35 AM Hao Ge <hao.ge@...ux.dev> wrote:
>>>>> From: Hao Ge <gehao@...inos.cn>
>>>>>
>>>>> After merge commit 233e89322cbe ("alloc_tag:
>>>>> fix module allocation tags populated area calculation"),
>>>>> We still encountered a KASAN bug.
>>>>>
>>>>> This is because we have only actually performed
>>>>> page allocation and address mapping here.
>>>>> we need to unpoisoned portions of underlying memory.
>>>>>
>>>>> Because we have a change in the size here,we need to
>>>>> re-annotate poisoned and unpoisoned portions of underlying memory
>>>>> according to the new size.
>>>>>
>>>>> Here is the log for KASAN:
>>>>>
>>>>> [ 5.041171][ T1]
>>>>> ==================================================================
>>>>> [ 5.042047][ T1] BUG: KASAN: vmalloc-out-of-bounds in
>>>>> move_module+0x2c0/0x708
>>>>> [ 5.042723][ T1] Write of size 240 at addr ffff80007e510000
>>>>> by task systemd/1
>>>>> [ 5.043412][ T1]
>>>>> [ 5.043523][ T72] input: QEMU QEMU USB Tablet as
>>>>> /devices/pci0000:00/0000:00:01.1/0000:02:001
>>>>> [ 5.043614][ T1] CPU: 0 UID: 0 PID: 1 Comm: systemd Not
>>>>> tainted 6.13.0-rc1+ #28
>>>>> [ 5.045560][ T1] Hardware name: QEMU KVM Virtual Machine,
>>>>> BIOS 0.0.0 02/06/2015
>>>>> [ 5.046328][ T1] Call trace:
>>>>> [ 5.046670][ T1] show_stack+0x20/0x38 (C)
>>>>> [ 5.047127][ T1] dump_stack_lvl+0x80/0xf8
>>>>> [ 5.047533][ T1]
>>>>> print_address_description.constprop.0+0x58/0x358
>>>>> [ 5.048092][ T72] hid-generic 0003:0627:0001.0001:
>>>>> input,hidraw0: USB HID v0.01 Mouse [QEMU 0
>>>>> [ 5.048126][ T1] print_report+0xb0/0x280
>>>>> [ 5.049682][ T1] kasan_report+0xb8/0x108
>>>>> [ 5.050170][ T1] kasan_check_range+0xe8/0x190
>>>>> [ 5.050685][ T1] memcpy+0x58/0xa0
>>>>> [ 5.051135][ T1] move_module+0x2c0/0x708
>>>>> [ 5.051586][ T1] layout_and_allocate.constprop.0+0x308/0x5b8
>>>>> [ 5.052219][ T1] load_module+0x134/0x16c8
>>>>> [ 5.052671][ T1] init_module_from_file+0xdc/0x138
>>>>> [ 5.053193][ T1] idempotent_init_module+0x344/0x600
>>>>> [ 5.053742][ T1] __arm64_sys_finit_module+0xbc/0x150
>>>>> [ 5.054289][ T1] invoke_syscall+0xd4/0x258
>>>>> [ 5.054749][ T1] el0_svc_common.constprop.0+0xb4/0x240
>>>>> [ 5.055319][ T1] do_el0_svc+0x48/0x68
>>>>> [ 5.055743][ T1] el0_svc+0x40/0xe0
>>>>> [ 5.056142][ T1] el0t_64_sync_handler+0x10c/0x138
>>>>> [ 5.056658][ T1] el0t_64_sync+0x1ac/0x1b0
>>>>>
>>>>> Fixes: 233e89322cbe ("alloc_tag: fix module allocation tags
>>>>> populated area calculation")
>>>>> Signed-off-by: Hao Ge <gehao@...inos.cn>
>>>> Thanks for the fix!
>>>>
>>>>> ---
>>>>> v2: Add comments to kasan_unpoison_vmalloc like other places.
>>>>>
>>>>> commit 233e89322cbe ("alloc_tag: fix module allocation
>>>>> tags populated area calculation") is currently in the
>>>>> mm-hotfixes-unstable branch, so this patch is
>>>>> developed based on the mm-hotfixes-unstable branch.
>>>>> ---
>>>>> lib/alloc_tag.c | 13 +++++++++++++
>>>>> 1 file changed, 13 insertions(+)
>>>>>
>>>>> diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
>>>>> index 4ee6caa6d2da..f885b3f3af0e 100644
>>>>> --- a/lib/alloc_tag.c
>>>>> +++ b/lib/alloc_tag.c
>>>>> @@ -421,7 +421,20 @@ static int vm_module_tags_populate(void)
>>>>> __free_page(next_page[i]);
>>>>> return -ENOMEM;
>>>>> }
>>>>> +
>>>>> + kasan_poison_vmalloc((void *)module_tags.start_addr,
>>>>> + vm_module_tags->nr_pages << PAGE_SHIFT);
>>>>> +
>>>>> vm_module_tags->nr_pages += nr;
>>>>> +
>>>>> + /*
>>>>> + * Mark the pages as accessible, now that they are
>>>>> mapped.
>>>>> + * With hardware tag-based KASAN, marking is
>>>>> skipped for
>>>>> + * non-VM_ALLOC mappings, see
>>>>> __kasan_unpoison_vmalloc().
>>>>> + */
>>>>> + kasan_unpoison_vmalloc((void
>>>>> *)module_tags.start_addr,
>>>>> + vm_module_tags->nr_pages << PAGE_SHIFT,
>>>>> + KASAN_VMALLOC_PROT_NORMAL);
>>>> Instead of poisoning [module_tags.start_addr,
>>>> vm_module_tags->nr_pages], incrementing vm_module_tags->nr_pages and
>>>> the unpoisoning [module_tags.start_addr, vm_module_tags->nr_pages]
>>>> could we simply poisons the additional area like this:
>>>>
>>>> kasan_unpoison_vmalloc((void
>>>> *)module_tags.start_addr +
>>>> (vm_module_tags->nr_pages << PAGE_SHIFT),
>>>> nr << PAGE_SHIFT,
>>>> KASAN_VMALLOC_PROT_NORMAL);
>>>> vm_module_tags->nr_pages += nr;
>>>> ?
>>>
>>> I had considered making such modifications earlier.
>>>
>>> But considering the following situation,
>>>
>>> A module tags spans across the regions of [module_tags.start_addr,
>>> vm_module_tags->nr_pages] and [module_tags.start_addr +
>>> vm_module_tags->nr_pages, ...].
>>>
>>> It may result in false positives for out-of-bounds errors.
>> Sorry, maybe I'm missing something but I don't see why poisoning only
>> newly mapped area would lead to false positives. Could you please
>> clarify?
>
>
> Because KASAN may perceive the two as distinct address spaces, despite
> their addresses being contiguous.
>
> So, when a module tag spans across these two contiguous address
> spaces, KASAN may incorrectly consider it as an out-of-bounds access.
>
>
>> Also, if you do need to unpoison and then poison, using phys_end and
>> new_end would be better, like this:
>>
>> kasan_poison_vmalloc((void *)module_tags.start_addr,
>> phys_end -
>> module_tags.start_addr)
>>
>> kasan_unpoison_vmalloc((void *)module_tags.start_addr,
>> new_end -
>> module_tags.start_addr,
>> KASAN_VMALLOC_PROT_NORMAL);
>
> OK, the next version will include.
After verification and consideration, I have found that this
modification may still pose problems.
Because we haven't ensured that new_end is page-aligned,
So, we've only made the region from||module_tags.start_addr
tonew_endaccessible.
Using this example, in reality,end equals 0xffff80007e5100f0:
Write of size 240 at addr ffff80007e510000 by task systemd/1
When we access other memory within the same page as0xffff80007e5100f0,
KASAN warnings will also be issued due to the lack of unpoisoned
portions in that memory.
Based on that, I would suggest sticking with the V2 version.
Thanks
Best Regards
Hao
>
>
> Thanks
>
> Best regards
>
> Hao
>
>
>>>
>>>>> }
>>>>>
>>>>> return 0;
>>>>> --
>>>>> 2.25.1
>>>>>
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