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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/12/25 10:16 PM, Lorenzo Stoakes wrote: > On Wed, Mar 12, 2025 at 08:04:23PM -0700, Yang Shi wrote: >> >> On 3/12/25 4:55 PM, Vasily Gorbik wrote: >>> On Wed, Mar 12, 2025 at 03:15:21PM -0700, Yang Shi wrote: >>>> LKP reported 800% performance improvement for small-allocs benchmark >>>> from vm-scalability [1] with patch ("/dev/zero: make private mapping >>>> full anonymous mapping") [2], but the patch was nack'ed since it changes >>>> the output of smaps somewhat. >>> ... >>>> --- >>>> v2: >>>> * Added the comments in code suggested by Lorenzo >>>> * Collected R-b from Lorenze >>>> >>>> mm/vma.c | 18 ++++++++++++++++-- >>>> 1 file changed, 16 insertions(+), 2 deletions(-) >>> Hi Yang, >>> >>> Replying to v2, as the code is the same as v1 in linux-next: >>> >>> The LTP test "mmap10" consistently triggers a kernel NULL pointer >>> dereference with this change, at least on x86 and s390. Reverting just >>> this single patch from linux-next fixes the issue. >> Hi Vasily, >> >> Thanks for the report. It is because dup_mmap() inserts the VMA into file >> rmap by checking whether vma->vm_file is NULL or not. This splat can be >> killed by skipping anonymous vma, but this actually will expose a more >> severe problem. The struct file refcount may be imbalance. The refcount is >> inc'ed in mmap, then inc'ed again by fork(), it is dec'ed when unmap or >> process exit. If we skip refcount inc in fork, we need skip refcount dec in >> unmap too, but there is still one refcount from mmap. >> >> Can we dec refcount in mmap if we see it is anonymous vma finally? >> Unfortunately, no. If the refcount reaches 0, the struct file will be freed. >> We will run into UAF when looking up smaps IIUC. It may point to anything. >> >> Lorenzo, >> >> This problem seems more complicated than what I thought in the first place. >> Making it is a real anonymous vma (vm_file is NULL) may be still the best >> option. But we need figure out how we can keep compatible smaps. > Ugh lord. I am not in favour of this for reasons aforementioned, and I _really_ > don't want to special case this any more than we already do... Yeah, understood. I meant we should find a way to make smaps unchanged or compatible. > > Let me think a bit about this also. > > Maybe if you're at LSF we can chat about it there? Unfortunately I can't make it this year. Have a fun! Thanks, Yang > > Thanks! > >> Andrew, >> >> Can you please drop this patch from your tree? >> >> Thanks, >> Yang >> >>> LTP: starting mmap10 >>> BUG: kernel NULL pointer dereference, address: 0000000000000008 >>> #PF: supervisor read access in kernel mode >>> #PF: error_code(0x0000) - not-present page >>> PGD 800000010d22a067 P4D 800000010d22a067 PUD 11ff09067 PMD 0 >>> Oops: Oops: 0000 [#1] PREEMPT SMP PTI >>> CPU: 5 UID: 0 PID: 1719 Comm: mmap10 Not tainted 6.14.0-rc6-next-20250312 #3 >>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-3.fc41 04/01/2014 >>> RIP: 0010:__rb_insert_augmented+0x2b/0x1d0 >>> Code: 0f 1e fa 48 89 f8 48 8b 3f 48 85 ff 0f 84 a4 01 00 00 41 55 49 89 f5 41 54 49 89 d4 55 53 48 8b 1f f6 c3 01 0f 85 e1 00 00 00 <48> 8b 53 08 48 39 fa 74 67 48 85 d2 74 09 f6 02 01 0f 84 a0 00 00 >>> RSP: 0018:ffffc90002b47cc8 EFLAGS: 00010246 >>> RAX: ffff8881143ab788 RBX: 0000000000000000 RCX: 00000000000009ff >>> RDX: ffffffff814ad5d0 RSI: ffff888100bb5060 RDI: ffff8881143ab088 >>> RBP: ffff8881053af8c0 R08: ffff8881143ab700 R09: 00007ff6433f2000 >>> R10: 00007ff6433f2000 R11: ffff8881143ab000 R12: ffffffff814ad5d0 >>> R13: ffff888100bb5060 R14: ffff8881143ab700 R15: ffff8881143ab000 >>> FS: 00007ff643df1740(0000) GS:ffff8882b45bf000(0000) knlGS:0000000000000000 >>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>> CR2: 0000000000000008 CR3: 000000011b042000 CR4: 00000000000006f0 >>> Call Trace: >>> >>> ? __die_body.cold+0x19/0x2b >>> ? page_fault_oops+0xc4/0x1f0 >>> ? search_extable+0x26/0x30 >>> ? search_module_extables+0x3f/0x60 >>> ? exc_page_fault+0x6b/0x150 >>> ? asm_exc_page_fault+0x26/0x30 >>> ? __pfx_vma_interval_tree_augment_rotate+0x10/0x10 >>> ? __pfx_vma_interval_tree_augment_rotate+0x10/0x10 >>> ? __rb_insert_augmented+0x2b/0x1d0 >>> copy_mm+0x48a/0x8c0 >>> copy_process+0xf98/0x1930 >>> kernel_clone+0xb7/0x3b0 >>> __do_sys_clone+0x65/0x90 >>> do_syscall_64+0x9e/0x1a0 >>> entry_SYSCALL_64_after_hwframe+0x77/0x7f >>> RIP: 0033:0x7ff643eb2b00 >>> Code: 31 c0 31 d2 31 f6 bf 11 00 20 01 48 89 e5 53 48 83 ec 08 64 48 8b 04 25 10 00 00 00 4c 8d 90 d0 02 00 00 b8 38 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 48 89 c3 85 c0 75 31 64 48 8b 04 25 10 00 00 >>> RSP: 002b:00007ffdac219010 EFLAGS: 00000202 ORIG_RAX: 0000000000000038 >>> RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007ff643eb2b00 >>> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000001200011 >>> RBP: 00007ffdac219020 R08: 0000000000000000 R09: 0000000000000000 >>> R10: 00007ff643df1a10 R11: 0000000000000202 R12: 0000000000000001 >>> R13: 0000000000000000 R14: 00007ff644036000 R15: 0000000000000000 >>> >>> Modules linked in: >>> CR2: 0000000000000008 >>> ---[ end trace 0000000000000000 ]--- >>> RIP: 0010:__rb_insert_augmented+0x2b/0x1d0 >>> Code: 0f 1e fa 48 89 f8 48 8b 3f 48 85 ff 0f 84 a4 01 00 00 41 55 49 89 f5 41 54 49 89 d4 55 53 48 8b 1f f6 c3 01 0f 85 e1 00 00 00 <48> 8b 53 08 48 39 fa 74 67 48 85 d2 74 09 f6 02 01 0f 84 a0 00 00 >>> RSP: 0018:ffffc90002b47cc8 EFLAGS: 00010246 >>> RAX: ffff8881143ab788 RBX: 0000000000000000 RCX: 00000000000009ff >>> RDX: ffffffff814ad5d0 RSI: ffff888100bb5060 RDI: ffff8881143ab088 >>> RBP: ffff8881053af8c0 R08: ffff8881143ab700 R09: 00007ff6433f2000 >>> R10: 00007ff6433f2000 R11: ffff8881143ab000 R12: ffffffff814ad5d0 >>> R13: ffff888100bb5060 R14: ffff8881143ab700 R15: ffff8881143ab000 >>> FS: 00007ff643df1740(0000) GS:ffff8882b45bf000(0000) knlGS:0000000000000000 >>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>> CR2: 0000000000000008 CR3: 000000011b042000 CR4: 00000000000006f0 >>> >>> >>> >>> LTP: starting mmap10 >>> Unable to handle kernel pointer dereference in virtual kernel address space >>> Failing address: 0000000000000000 TEID: 0000000000000483 >>> Fault in home space mode while using kernel ASCE. >>> AS:000000000247c007 R3:00000001ffffc007 S:00000001ffffb801 P:000000000000013d >>> Oops: 0004 ilc:3 [#1] SMP >>> Modules linked in: >>> CPU: 0 UID: 0 PID: 665 Comm: mmap10 Not tainted 6.14.0-rc6-next-20250312 #16 >>> Hardware name: IBM 3931 A01 704 (KVM/Linux) >>> Krnl PSW : 0704c00180000000 000003ffe0ee0440 (__rb_insert_augmented+0x60/0x210) >>> R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:0 PM:0 RI:0 EA:3 >>> Krnl GPRS: 00000000009ff000 0000000000000000 000000008e5f7508 0000000084a7ed08 >>> 00000000000009fe 0000000000000000 0000000000000000 0000037fe06c7b68 >>> 00000000801d0e90 000003ffe04158d0 0000000084a7ed08 0000000000000000 >>> 000003ffbb700000 00000000801d0e48 000003ffe0ee057c 0000037fe06c7a40 >>> Krnl Code: 000003ffe0ee0430: e31030080004 lg %r1,8(%r3) >>> 000003ffe0ee0436: ec1200888064 cgrj %r1,%r2,8,000003ffe0ee0546 >>> #000003ffe0ee043c: b90400a3 lgr %r10,%r3 >>> >000003ffe0ee0440: e310b0100024 stg %r1,16(%r11) >>> 000003ffe0ee0446: e3b030080024 stg %r11,8(%r3) >>> 000003ffe0ee044c: ec180009007c cgij %r1,0,8,000003ffe0ee045e >>> 000003ffe0ee0452: ec2b000100d9 aghik %r2,%r11,1 >>> 000003ffe0ee0458: e32010000024 stg %r2,0(%r1) >>> Call Trace: >>> [<000003ffe0ee0440>] __rb_insert_augmented+0x60/0x210 >>> [<000003ffe016d6c4>] dup_mmap+0x424/0x8c0 >>> [<000003ffe016dc62>] copy_mm+0x102/0x1c0 >>> [<000003ffe016e8ae>] copy_process+0x7ce/0x12b0 >>> [<000003ffe016f458>] kernel_clone+0x68/0x380 >>> [<000003ffe016f84a>] __do_sys_clone+0x5a/0x70 >>> [<000003ffe016faa0>] __s390x_sys_clone+0x40/0x50 >>> [<000003ffe011c9b6>] do_syscall.constprop.0+0x116/0x140 >>> [<000003ffe0ef1d64>] __do_syscall+0xd4/0x1c0 >>> [<000003ffe0efd044>] system_call+0x74/0x98 >>> Last Breaking-Event-Address: >>> [<000003ffe0ee058a>] __rb_insert_augmented+0x1aa/0x210 >>> Kernel panic - not syncing: Fatal exception: panic_on_oops