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Message-ID: <7693a84-bdc2-27b5-2695-d0fe8566571f@google.com>
Date: Fri, 23 Sep 2022 17:14:38 -0700 (PDT)
From: Hugh Dickins <hughd@...gle.com>
To: Mike Kravetz <mike.kravetz@...cle.com>
cc: Peter Xu <peterx@...hat.com>,
Axel Rasmussen <axelrasmussen@...gle.com>,
Yang Shi <shy828301@...il.com>,
Matthew Wilcox <willy@...radead.org>,
syzbot <syzbot+152d76c44ba142f8992b@...kaller.appspotmail.com>,
Hugh Dickins <hughd@...gle.com>, akpm@...ux-foundation.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
llvm@...ts.linux.dev, nathan@...nel.org, ndesaulniers@...gle.com,
songmuchun@...edance.com, syzkaller-bugs@...glegroups.com,
trix@...hat.com
Subject: Re: [syzbot] general protection fault in PageHeadHuge
On Fri, 23 Sep 2022, Mike Kravetz wrote:
> On 09/23/22 09:05, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit: 483fed3b5dc8 Add linux-next specific files for 20220921
> > git tree: linux-next
> > console output: https://syzkaller.appspot.com/x/log.txt?x=16f0a418880000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=849cb9f70f15b1ba
> > dashboard link: https://syzkaller.appspot.com/bug?extid=152d76c44ba142f8992b
> > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12b97b64880000
> > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11fb9040880000
> >
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/1cb3f4618323/disk-483fed3b.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/cc02cb30b495/vmlinux-483fed3b.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+152d76c44ba142f8992b@...kaller.appspotmail.com
> >
> > general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN
> > KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> > CPU: 1 PID: 3617 Comm: syz-executor722 Not tainted 6.0.0-rc6-next-20220921-syzkaller #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2022
> > RIP: 0010:PagePoisoned include/linux/page-flags.h:304 [inline]
> > RIP: 0010:PageHead include/linux/page-flags.h:787 [inline]
> > RIP: 0010:PageHeadHuge+0x1d/0x200 mm/hugetlb.c:1892
> > Code: ff 66 66 2e 0f 1f 84 00 00 00 00 00 90 41 54 55 48 89 fd 53 e8 54 c9 b9 ff 48 89 ea 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 <80> 3c 02 00 0f 85 a2 01 00 00 48 8b 5d 00 48 c7 c7 ff ff ff ff 48
> > RSP: 0018:ffffc90003e7f5a0 EFLAGS: 00010246
> > RAX: dffffc0000000000 RBX: ffffc90003e7f788 RCX: 0000000000000000
> > RDX: 0000000000000000 RSI: ffffffff81c2cb2c RDI: 0000000000000000
> > RBP: 0000000000000000 R08: 0000000000000005 R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000001 R12: ffffc90003e7f798
> > R13: 0000000000000000 R14: 0000000000000000 R15: 00000000000003f4
> > FS: 00007f5642262700(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000
> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 00000000203f4ef0 CR3: 000000007adcc000 CR4: 00000000003506e0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> > <TASK>
> > folio_test_hugetlb include/linux/page-flags.h:831 [inline]
> > folio_file_page include/linux/pagemap.h:683 [inline]
> > shmem_fault+0x27c/0x8a0 mm/shmem.c:2130
> > __do_fault+0x107/0x600 mm/memory.c:4191
> > do_shared_fault mm/memory.c:4597 [inline]
> > do_fault mm/memory.c:4675 [inline]
> > handle_pte_fault mm/memory.c:4943 [inline]
> > __handle_mm_fault+0x2200/0x3a40 mm/memory.c:5085
> > handle_mm_fault+0x1c8/0x780 mm/memory.c:5206
> > do_user_addr_fault+0x475/0x1210 arch/x86/mm/fault.c:1428
> > handle_page_fault arch/x86/mm/fault.c:1519 [inline]
> > exc_page_fault+0x94/0x170 arch/x86/mm/fault.c:1575
> > asm_exc_page_fault+0x22/0x30 arch/x86/include/asm/idtentry.h:570
> > RIP: 0010:__put_user_nocheck_4+0x3/0x11
> > Code: 00 00 48 39 d9 73 54 0f 01 cb 66 89 01 31 c9 0f 01 ca c3 0f 1f 44 00 00 48 bb fd ef ff ff ff 7f 00 00 48 39 d9 73 34 0f 01 cb <89> 01 31 c9 0f 01 ca c3 66 0f 1f 44 00 00 48 bb f9 ef ff ff ff 7f
> > RSP: 0018:ffffc90003e7fa00 EFLAGS: 00050293
> > RAX: 0000000000000000 RBX: ffffc90003e7fdf4 RCX: 00000000203f4ef0
> > RDX: ffff888020c51d40 RSI: ffffffff8726d52f RDI: 0000000000000005
> > RBP: ffffc90003e7fdb0 R08: 0000000000000005 R09: 0000000000000000
> > R10: 0000000000000002 R11: 0000000000000001 R12: 0000000000000000
> > R13: 0000000000000002 R14: 00000000203f4ef0 R15: 0000000000000000
> > ____sys_recvmsg+0x3ba/0x610 net/socket.c:2714
> > ___sys_recvmsg+0xf2/0x180 net/socket.c:2743
> > do_recvmmsg+0x25e/0x6e0 net/socket.c:2837
> > __sys_recvmmsg net/socket.c:2916 [inline]
> > __do_sys_recvmmsg net/socket.c:2939 [inline]
> > __se_sys_recvmmsg net/socket.c:2932 [inline]
> > __x64_sys_recvmmsg+0x20b/0x260 net/socket.c:2932
> > do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> > entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > RIP: 0033:0x7f56422dabb9
> > Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 91 18 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
> > RSP: 002b:00007f5642262208 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
> > RAX: ffffffffffffffda RBX: 00007f564235c4b8 RCX: 00007f56422dabb9
> > RDX: 0000000000010106 RSI: 00000000200000c0 RDI: 0000000000000003
> > RBP: 00007f564235c4b0 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000002 R11: 0000000000000246 R12: 00007f564235c4bc
> > R13: 00007fffbde3618f R14: 00007f5642262300 R15: 0000000000022000
> > </TASK>
> > Modules linked in:
> > ---[ end trace 0000000000000000 ]---
>
> While it is true that the addressing exception is happening in the hugetlb
> routine PageHeadHuge(), the reason is because it is passed a NULL page
> pointer. This is via the call to folio_file_page() at the end of shmem_fault.
>
> err = shmem_get_folio_gfp(inode, vmf->pgoff, &folio, SGP_CACHE,
> gfp, vma, vmf, &ret);
> if (err)
> return vmf_error(err);
>
> vmf->page = folio_file_page(folio, vmf->pgoff);
> return ret;
>
> The code assumes that if a non-zero value is returned from shmem_get_folio_gfp,
> then folio pointer will be set to a folio. However, it looks like there are
> a few places in shmem_get_folio_gfp where it will return zero and not set
> folio.
>
> In this specific case, it is the code block:
>
> if (vma && userfaultfd_missing(vma)) {
> *fault_type = handle_userfault(vmf, VM_UFFD_MISSING);
> return 0;
> }
>
> I could try to sort this out, but I believe Matthew has the most context as
> he has been changing this code recently.
Thanks Mike. Yes, it looks like userfaultfd's successful returns from
shmem_get_folio_gfp() have (correctly?) filled in vmf->page directly,
and are not setting *foliop at all. So this would affect any
userfaultfd usage of shmem, not just an odd syzbot corner case.
I do think shmem_fault() ought at least to initialize its folio pointer
(as shmem_file_read_iter() correctly does); and if it does that, then we
don't need to weed out the userfaultfd cases as such, but just avoid
folio_file_page() when folio is still NULL.
I've neither tried the syzbot test case (but see its .c does involve
userfaultld), nor tried userfaultfd shmem: Peter, could you give this a
try - we'd expect userfaultfd shmem to crash on linux-next without the
patch below.
And it implies that nobody has been trying userfaultfd shmem on recent
linux-next, so whether vmf->page is then set correctly we're not sure.
But me, I cannot even get the latest linux-next to boot: next job.
Hugh
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2060,7 +2060,7 @@ static vm_fault_t shmem_fault(struct vm_fault *vmf)
struct vm_area_struct *vma = vmf->vma;
struct inode *inode = file_inode(vma->vm_file);
gfp_t gfp = mapping_gfp_mask(inode->i_mapping);
- struct folio *folio;
+ struct folio *folio = NULL;
int err;
vm_fault_t ret = VM_FAULT_LOCKED;
@@ -2127,7 +2127,8 @@ static vm_fault_t shmem_fault(struct vm_fault *vmf)
gfp, vma, vmf, &ret);
if (err)
return vmf_error(err);
- vmf->page = folio_file_page(folio, vmf->pgoff);
+ if (folio)
+ vmf->page = folio_file_page(folio, vmf->pgoff);
return ret;
}
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