On Wed, Sep 29, 2021 at 03:21:09PM +0000, Sean Christopherson wrote: > On Tue, Sep 28, 2021, Stephen wrote: > > Hello, > > > > I got this crash again on 5.14.7 in the early morning of the 27th. > > Things hung up shortly after I'd gone to bed. Uptime was 1 day 9 hours 9 > > minutes. > > ... > > > BUG: kernel NULL pointer dereference, address: 0000000000000068 > > #PF: supervisor read access in kernel mode > > #PF: error_code(0x0000) - not-present page > > PGD 0 P4D 0 > > Oops: 0000 [#1] SMP NOPTI > > CPU: 21 PID: 8494 Comm: CPU 7/KVM Tainted: G E 5.14.7 #32 > > Hardware name: Gigabyte Technology Co., Ltd. X570 AORUS ELITE WIFI/X570 > > AORUS ELITE WIFI, BIOS F35 07/08/2021 > > RIP: 0010:internal_get_user_pages_fast+0x738/0xda0 > > Code: 84 24 a0 00 00 00 65 48 2b 04 25 28 00 00 00 0f 85 54 06 00 00 48 > > 81 c4 a8 00 00 00 44 89 e0 5b 5d 41 5c 41 5d 41 5e 41 5f c3 <48> 81 78 > > 68 a0 a3 > > > I haven't reproduced the crash, but the code signature (CMP against an absolute > address) is quite distinct, and is consistent across all three crashes. I'm pretty > sure the issue is that page_is_secretmem() doesn't check for a null page->mapping, > e.g. if the page is truncated, which IIUC can happen in parallel since gup() doesn't > hold the lock. > > I think this should fix the problems? > > diff --git a/include/linux/secretmem.h b/include/linux/secretmem.h > index 21c3771e6a56..988528b5da43 100644 > --- a/include/linux/secretmem.h > +++ b/include/linux/secretmem.h > @@ -23,7 +23,7 @@ static inline bool page_is_secretmem(struct page *page) > mapping = (struct address_space *) > ((unsigned long)page->mapping & ~PAGE_MAPPING_FLAGS); > > - if (mapping != page->mapping) > + if (!mapping || mapping != page->mapping) I'll roll this out on my vm host and try to re-run the mass fuzztest overnight, though IT claims they're going to kill power to the whole datacenter until Monday(!)... --D > return false; > > return mapping->a_ops == &secretmem_aops;
