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Message-ID: <3b893634-5453-42d0-b8dc-e9d07988e9e9@redhat.com>
Date: Tue, 18 Feb 2025 09:23:39 +0100
From: David Hildenbrand <david@...hat.com>
To: Tong Tiangen <tongtiangen@...wei.com>,
Masami Hiramatsu <mhiramat@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>,
"Liang, Kan" <kan.liang@...ux.intel.com>,
Andrew Morton <akpm@...ux-foundation.org>, Peter Xu <peterx@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
linux-perf-users@...r.kernel.org, bpf@...r.kernel.org,
wangkefeng.wang@...wei.com, linux-mm <linux-mm@...ck.org>
Subject: Re: Add Morton,Peter and David for discussion//Re: [PATCH -next]
uprobes: fix two zero old_folio bugs in __replace_page()
On 18.02.25 03:47, Tong Tiangen wrote:
>
>
> 在 2025/2/17 20:38, Tong Tiangen 写道:
>> We triggered the following error logs in syzkaller test:
>>
>> BUG: Bad page state in process syz.7.38 pfn:1eff3
>> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1eff3
>> flags: 0x3fffff00004004(referenced|reserved|node=0|zone=1|lastcpupid=0x1fffff)
>> raw: 003fffff00004004 ffffe6c6c07bfcc8 ffffe6c6c07bfcc8 0000000000000000
>> raw: 0000000000000000 0000000000000000 00000000fffffffe 0000000000000000
>> page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
>> Call Trace:
>> <TASK>
>> dump_stack_lvl+0x32/0x50
>> bad_page+0x69/0xf0
>> free_unref_page_prepare+0x401/0x500
>> free_unref_page+0x6d/0x1b0
>> uprobe_write_opcode+0x460/0x8e0
>> install_breakpoint.part.0+0x51/0x80
>> register_for_each_vma+0x1d9/0x2b0
>> __uprobe_register+0x245/0x300
>> bpf_uprobe_multi_link_attach+0x29b/0x4f0
>> link_create+0x1e2/0x280
>> __sys_bpf+0x75f/0xac0
>> __x64_sys_bpf+0x1a/0x30
>> do_syscall_64+0x56/0x100
>> entry_SYSCALL_64_after_hwframe+0x78/0xe2
>>
>> BUG: Bad rss-counter state mm:00000000452453e0 type:MM_FILEPAGES val:-1
>>
>> The following syzkaller test case can be used to reproduce:
>>
>> r2 = creat(&(0x7f0000000000)='./file0\x00', 0x8)
>> write$nbd(r2, &(0x7f0000000580)=ANY=[], 0x10)
>> r4 = openat(0xffffffffffffff9c, &(0x7f0000000040)='./file0\x00', 0x42, 0x0)
>> mmap$IORING_OFF_SQ_RING(&(0x7f0000ffd000/0x3000)=nil, 0x3000, 0x0, 0x12, r4, 0x0)
>> r5 = userfaultfd(0x80801)
>> ioctl$UFFDIO_API(r5, 0xc018aa3f, &(0x7f0000000040)={0xaa, 0x20})
>> r6 = userfaultfd(0x80801)
>> ioctl$UFFDIO_API(r6, 0xc018aa3f, &(0x7f0000000140))
>> ioctl$UFFDIO_REGISTER(r6, 0xc020aa00, &(0x7f0000000100)={{&(0x7f0000ffc000/0x4000)=nil, 0x4000}, 0x2})
>> ioctl$UFFDIO_ZEROPAGE(r5, 0xc020aa04, &(0x7f0000000000)={{&(0x7f0000ffd000/0x1000)=nil, 0x1000}})
>> r7 = bpf$PROG_LOAD(0x5, &(0x7f0000000140)={0x2, 0x3, &(0x7f0000000200)=ANY=[@ANYBLOB="1800000000120000000000000000000095"], &(0x7f0000000000)='GPL\x00', 0x7, 0x0, 0x0, 0x0, 0x0, '\x00', 0x0, @fallback=0x30, 0xffffffffffffffff, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x10, 0x0, @void, @value}, 0x94)
>> bpf$BPF_LINK_CREATE_XDP(0x1c, &(0x7f0000000040)={r7, 0x0, 0x30, 0x1e, @val=@...obe_multi={&(0x7f0000000080)='./file0\x00', &(0x7f0000000100)=[0x2], 0x0, 0x0, 0x1}}, 0x40)
>>
>> The cause is that zero pfn is set to the pte without increasing the rss
>> count in mfill_atomic_pte_zeropage() and the refcount of zero folio does
>> not increase accordingly. Then, the operation on the same pfn is performed
>> in uprobe_write_opcode()->__replace_page() to unconditional decrease the
>> rss count and old_folio's refcount.
>>
>> Therefore, two bugs are introduced:
>> 1. The rss count is incorrect, when process exit, the check_mm() report
>> error "Bad rss-count".
>> 2. The reserved folio (zero folio) is freed when folio->refcount is zero,
>> then free_pages_prepare->free_page_is_bad() report error "Bad page state".
>>
>> To fix it, add zero folio check before rss counter and refcount decrease.
>>
>> Fixes: 7396fa818d62 ("uprobes/core: Make background page replacement logic account for rss_stat counters")
>> Fixes: 2b1444983508 ("uprobes, mm, x86: Add the ability to install and remove uprobes breakpoints")
>> Signed-off-by: Tong Tiangen <tongtiangen@...wei.com>
>> ---
>> kernel/events/uprobes.c | 6 ++++--
>> 1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
>> index 46ddf3a2334d..ff5694acfa68 100644
>> --- a/kernel/events/uprobes.c
>> +++ b/kernel/events/uprobes.c
>> @@ -213,7 +213,8 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
>> dec_mm_counter(mm, MM_ANONPAGES);
>>
>> if (!folio_test_anon(old_folio)) {
>> - dec_mm_counter(mm, mm_counter_file(old_folio));
>> + if (!is_zero_folio(old_folio))
>> + dec_mm_counter(mm, mm_counter_file(old_folio));
>> inc_mm_counter(mm, MM_ANONPAGES);
>> }
>>
>> @@ -227,7 +228,8 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
>> if (!folio_mapped(old_folio))
>> folio_free_swap(old_folio);
>> page_vma_mapped_walk_done(&pvmw);
>> - folio_put(old_folio);
>> + if (!is_zero_folio(old_folio))
>> + folio_put(old_folio);
>> >> err = 0;
>> unlock:
>
The whole "manually replace pages" logic is fragile. I tried to rewrite
it a while back:
https://lkml.kernel.org/r/20240604122548.359952-1-david@redhat.com
But didn't get to follow-up yet.
I'm not sure if the page_vma_mapped_walk() really does what we would
expect here.
The folio_remove_rmap_pte(old_folio, old_page, vma); is certainly wrong
as well for ero folios.
I don't think there is a sane use case right now where we would hit the
shared zeropage.
So for the time being, I think we should just reject them immediately
after get_user_page_vma_remote().
At some point I'll follow up with my rewrite that will clean this
nastiness here up a bit.
--
Cheers,
David / dhildenb
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