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Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Add Morton,Peter and David for discussion//Re: [PATCH -next] uprobes: fix two zero old_folio bugs in __replace_page() To: Masami Hiramatsu , Oleg Nesterov , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , "Liang, Kan" , Andrew Morton , Peter Xu , David Hildenbrand CC: , , , , , linux-mm References: <20250217123826.88503-1-tongtiangen@huawei.com> From: Tong Tiangen In-Reply-To: <20250217123826.88503-1-tongtiangen@huawei.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To kwepemk500005.china.huawei.com (7.202.194.90) 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: > > 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=@uprobe_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 > --- > 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: