Messages in this thread | | | Subject | Re: [PATCH] kvm_s390_vm_start_migration: check dirty_bitmap before using it as target for memset() | From | David Hildenbrand <> | Date | Mon, 9 Sep 2019 18:22:16 +0200 |
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On 09.09.19 18:17, Igor Mammedov wrote: > On Mon, 9 Sep 2019 17:47:37 +0200 > David Hildenbrand <david@redhat.com> wrote: > >> On 09.09.19 16:55, Igor Mammedov wrote: >>> If userspace doesn't set KVM_MEM_LOG_DIRTY_PAGES on memslot before calling >>> kvm_s390_vm_start_migration(), kernel will oops with: >>> >> >> We usually have the subject in a "KVM: s390: ..." format. Like >> >> "KVM: s390: check dirty_bitmap before using it as target for memset()" >> >>> 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:0000000002a2000b R2:00000001bff8c00b R3:00000001bff88007 S:00000001bff91000 P:000000000000003d >>> Oops: 0004 ilc:2 [#1] SMP >>> ... >>> Call Trace: >>> ([<001fffff804ec552>] kvm_s390_vm_set_attr+0x347a/0x3828 [kvm]) >>> [<001fffff804ecfc0>] kvm_arch_vm_ioctl+0x6c0/0x1998 [kvm] >>> [<001fffff804b67e4>] kvm_vm_ioctl+0x51c/0x11a8 [kvm] >>> [<00000000008ba572>] do_vfs_ioctl+0x1d2/0xe58 >>> [<00000000008bb284>] ksys_ioctl+0x8c/0xb8 >>> [<00000000008bb2e2>] sys_ioctl+0x32/0x40 >>> [<000000000175552c>] system_call+0x2b8/0x2d8 >>> INFO: lockdep is turned off. >>> Last Breaking-Event-Address: >>> [<0000000000dbaf60>] __memset+0xc/0xa0 >>> >>> due to ms->dirty_bitmap being NULL, which migh crash the host. >> >> s/migh/might/ >> >>> >>> Make sure that ms->dirty_bitmap is set before using it or >>> print a warning and return -ENIVAL otherwise. >>> >>> Signed-off-by: Igor Mammedov <imammedo@redhat.com> >>> --- >>> >>> PS: >>> keeping it private for now as issue might DoS host, >>> I'll leave it upto maintainers to decide if it should be handled as security >>> bug (I'm not sure what process for handling such bugs should be used). >>> >>> >>> arch/s390/kvm/kvm-s390.c | 4 ++++ >>> 1 file changed, 4 insertions(+) >>> >>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c >>> index f329dcb3f44c..dfba51c9d60c 100644 >>> --- a/arch/s390/kvm/kvm-s390.c >>> +++ b/arch/s390/kvm/kvm-s390.c >>> @@ -1018,6 +1018,10 @@ static int kvm_s390_vm_start_migration(struct kvm *kvm) >>> /* mark all the pages in active slots as dirty */ >>> for (slotnr = 0; slotnr < slots->used_slots; slotnr++) { >>> ms = slots->memslots + slotnr; >>> + if (!ms->dirty_bitmap) { >>> + WARN(1, "ms->dirty_bitmap == NULL\n"); >>> + return -EINVAL; >>> + } >> >> if (WARN_ON_ONCE(!ms->dirty_bitmap)) >> return -EINVAL; >> >> But I wonder if the WARN is really needed. (or simply a wrong usage of the interface) > I added WARN because of there is no any visible sign that something > went wrong in userspace, this way at least we would have a trace of > invalid API usage. > > But I can drop it if you prefer.
Yeah, I understand the rational, but WARN's should usually not be triggered from user space (and -EINVAL is some telling user space already that it is doing something wrong). If you care about a notification maybe use a pr_warn_ratelimited() instead. Otherwise, I suggest updating the documentation in which cases one could get -EINVAL.
Thanks!
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Thanks,
David / dhildenb
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