Messages in this thread | | | Date | Thu, 16 Nov 2023 12:04:35 +0200 | From | José Pekkarinen <> | Subject | Re: [PATCH] mm/pgtable: return null if no ptl in __pte_offset_map_lock |
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On 2023-11-16 07:23, Hugh Dickins wrote: > On Wed, 15 Nov 2023, Matthew Wilcox wrote: >> On Wed, Nov 15, 2023 at 06:05:30PM +0200, José Pekkarinen wrote: >> >> > > I don't think we should be changing ptlock_ptr(). >> > >> > This is where the null ptr dereference originates, so the only >> > alternative I can think of is to protect the life cycle of the ptdesc >> > to prevent it to die between the pte check and the spin_unlock of >> > __pte_offset_map_lock. Would that work for you? > > Thanks for pursuing this, José, but I agree with Matthew: I don't > think your patch is right at all. The change in ptlock_ptr() did not > make sense to me, and the change in __pte_offset_map_lock() leaves us > still wondering what has gone wrong (and misses an rcu_read_unlock()). > > You mentioned "I tested the syzbot reproducer in x86 and it doesn't > produce this kasan report anymore": are you saying that you were able > to reproduce the issue on x86 (without your patch)? That would be very > interesting (and I think would disprove my hypothesis below). I ought > to try on x86 if you managed to reproduce on it, but it's not worth > the effort if you did not. If you have an x86 stack and registers, > please show (though I'm uncertain how much KASAN spoils the output).
Hi,
Yes, I have a local setup based in [1], where I can spin a small vm, build the reproducer and run it in. The only thing I took from the webpage is the kernel config file, and the image I made it locally by debootstrapping and running the modifications in create-image.sh manually, the kasan report follows:
[ 111.408746][ T8885] general protection fault, probably for non-canonical address 0xdffffc0000000005: 0000 [#1] PREEMPT SMP KASAN NOPTI [ 111.413181][ T8885] KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f] [ 111.413181][ T8885] CPU: 1 PID: 8885 Comm: handle_kernel_p Not tainted 6.7.0-rc1-00007-ge612cb00e200 #6 [ 111.413181][ T8885] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 [ 111.413181][ T8885] RIP: 0010:__pte_offset_map_lock+0xfa/0x310 [ 111.423642][ T8885] Code: 48 c1 e8 03 80 3c 10 00 0f 85 12 02 00 00 4c 03 3d db 92 cf 0b 48 b8 00 00 00 00 00 fc ff df 49 8d 7f 28 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 e2 01 00 00 4d 8b 7f 28 4c 89 ff e8 f0 a1 3a 09 [ 111.423642][ T8885] RSP: 0018:ffffc90005baf738 EFLAGS: 00010216 [ 111.423642][ T8885] RAX: dffffc0000000000 RBX: 0005800000000067 RCX: ffffffff81ada02e [ 111.423642][ T8885] RDX: 0000000000000005 RSI: ffffffff81ad9f0f RDI: 0000000000000028 [ 111.423642][ T8885] RBP: ffff8880224c4800 R08: 0000000000000007 R09: 0000000000000000 [ 111.423642][ T8885] R10: 0000000000000000 R11: 0000000000000000 R12: 0005088000000a80 [ 111.423642][ T8885] R13: 1ffff92000b75ee9 R14: ffffc90005bafa88 R15: 0000000000000000 [ 111.423642][ T8885] FS: 00007f8d3972c6c0(0000) GS:ffff888069700000(0000) knlGS:0000000000000000 [ 111.423642][ T8885] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 111.423642][ T8885] CR2: 00007f8d3970af78 CR3: 00000000224d6000 CR4: 00000000000006f0 [ 111.423642][ T8885] Call Trace: [ 111.423642][ T8885] <TASK> [ 111.423642][ T8885] ? show_regs+0x8f/0xa0 [ 111.423642][ T8885] ? die_addr+0x4f/0xd0 [ 111.423642][ T8885] ? exc_general_protection+0x150/0x220 [ 111.423642][ T8885] ? asm_exc_general_protection+0x26/0x30 [ 111.423642][ T8885] ? __pte_offset_map_lock+0x1de/0x310 [ 111.423642][ T8885] ? __pte_offset_map_lock+0xbf/0x310 [ 111.423642][ T8885] ? __pte_offset_map_lock+0xfa/0x310 [ 111.423642][ T8885] ? __pte_offset_map_lock+0xbf/0x310 [ 111.423642][ T8885] ? __pfx___pte_offset_map_lock+0x10/0x10 [ 111.423642][ T8885] filemap_map_pages+0x336/0x13b0 [ 111.423642][ T8885] ? __pfx_filemap_map_pages+0x10/0x10 [ 111.423642][ T8885] ? rcu_read_unlock+0x33/0xb0 [ 111.423642][ T8885] do_fault+0x86a/0x1350 [ 111.423642][ T8885] __handle_mm_fault+0xe53/0x23a0 [ 111.423642][ T8885] ? __pfx___handle_mm_fault+0x10/0x10 [ 111.483413][ T8885] handle_mm_fault+0x369/0x890 [ 111.483413][ T8885] __get_user_pages+0x46d/0x15d0 [ 111.483413][ T8885] ? __pfx___get_user_pages+0x10/0x10 [ 111.483413][ T8885] populate_vma_page_range+0x2de/0x420 [ 111.483413][ T8885] ? __pfx_populate_vma_page_range+0x10/0x10 [ 111.483413][ T8885] ? __pfx_find_vma_intersection+0x10/0x10 [ 111.483413][ T8885] ? vm_mmap_pgoff+0x299/0x3c0 [ 111.483413][ T8885] __mm_populate+0x1da/0x380 [ 111.483413][ T8885] ? __pfx___mm_populate+0x10/0x10 [ 111.483413][ T8885] ? up_write+0x1b3/0x520 [ 111.483413][ T8885] vm_mmap_pgoff+0x2d1/0x3c0 [ 111.483413][ T8885] ? __pfx_vm_mmap_pgoff+0x10/0x10 [ 111.483413][ T8885] ksys_mmap_pgoff+0x7d/0x5b0 [ 111.483413][ T8885] __x64_sys_mmap+0x125/0x190 [ 111.483413][ T8885] do_syscall_64+0x45/0xf0 [ 111.483413][ T8885] entry_SYSCALL_64_after_hwframe+0x6e/0x76 [ 111.483413][ T8885] RIP: 0033:0x7f8d39831559 [ 111.483413][ T8885] Code: 08 89 e8 5b 5d c3 66 2e 0f 1f 84 00 00 00 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 8b 0d 77 08 0d 00 f7 d8 64 89 01 48 [ 111.483413][ T8885] RSP: 002b:00007f8d3972be78 EFLAGS: 00000216 ORIG_RAX: 0000000000000009 [ 111.483413][ T8885] RAX: ffffffffffffffda RBX: 00007f8d3972c6c0 RCX: 00007f8d39831559 [ 111.483413][ T8885] RDX: b635773f07ebbeea RSI: 0000000000b36000 RDI: 0000000020000000 [ 111.483413][ T8885] RBP: 00007f8d3972bea0 R08: 00000000ffffffff R09: 0000000000000000 [ 111.483413][ T8885] R10: 0000000000008031 R11: 0000000000000216 R12: ffffffffffffff80 [ 111.483413][ T8885] R13: 0000000000000000 R14: 00007fffcef921d0 R15: 00007f8d3970c000 [ 111.483413][ T8885] </TASK> [ 111.483413][ T8885] Modules linked in: [ 111.763549][ T8885] ---[ end trace 0000000000000000 ]--- [ 111.773557][ T8885] RIP: 0010:__pte_offset_map_lock+0xfa/0x310 [ 111.776045][ T8885] Code: 48 c1 e8 03 80 3c 10 00 0f 85 12 02 00 00 4c 03 3d db 92 cf 0b 48 b8 00 00 00 00 00 fc ff df 49 8d 7f 28 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 e2 01 00 00 4d 8b 7f 28 4c 89 ff e8 f0 a1 3a 09 [ 111.805040][ T8885] RSP: 0018:ffffc90005baf738 EFLAGS: 00010216 [ 111.820041][ T8885] RAX: dffffc0000000000 RBX: 0005800000000067 RCX: ffffffff81ada02e [ 111.837884][ T8885] RDX: 0000000000000005 RSI: ffffffff81ad9f0f RDI: 0000000000000028 [ 111.855313][ T8885] RBP: ffff8880224c4800 R08: 0000000000000007 R09: 0000000000000000 [ 111.878314][ T8885] R10: 0000000000000000 R11: 0000000000000000 R12: 0005088000000a80 [ 111.910624][ T8885] R13: 1ffff92000b75ee9 R14: ffffc90005bafa88 R15: 0000000000000000 [ 111.923627][ T8885] FS: 00007f8d3972c6c0(0000) GS:ffff888069700000(0000) knlGS:0000000000000000 [ 111.932017][ T8885] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 111.941166][ T8885] CR2: 00007fa26ac38178 CR3: 00000000224d6000 CR4: 00000000000006f0 [ 111.950619][ T8885] Kernel panic - not syncing: Fatal exception [ 111.953981][ T8885] Kernel Offset: disabled [ 111.953981][ T8885] Rebooting in 86400 seconds..
I can test some patches for you if it helps finding out the issue.
[1] https://github.com/google/syzkaller/blob/master/docs/linux/setup_ubuntu-host_qemu-vm_x86-64-kernel.md
José.
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