KASAN: null-ptr-deref Read in kvm_arch_check_processor_compat

KASAN: null-ptr-deref Read in kvm_arch_check_processor_compat

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    7ae77150 Merge tag 'powerpc-5.8-1' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=135e7235100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d195fe572fb15312
dashboard link: https://syzkaller.appspot.com/bug?extid=a99874f5323ce6088e53
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14d001be100000

Bisection is inconclusive: the bug happens on the oldest tested release.

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=13a8e549100000
final crash:    https://syzkaller.appspot.com/x/report.txt?x=1068e549100000
console output: https://syzkaller.appspot.com/x/log.txt?x=17a8e549100000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+a99874f5323ce6088e53@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: null-ptr-deref in test_bit include/asm-generic/bitops/instrumented-non-atomic.h:110 [inline]
BUG: KASAN: null-ptr-deref in kvm_arch_check_processor_compat+0x1f8/0x750 arch/x86/kvm/x86.c:9818
Read of size 8 at addr 0000000000000060 by task syz-executor.2/8085

CPU: 1 PID: 8085 Comm: syz-executor.2 Not tainted 5.7.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x188/0x20d lib/dump_stack.c:118
 __kasan_report mm/kasan/report.c:517 [inline]
 kasan_report.cold+0x5/0x37 mm/kasan/report.c:530
 check_memory_region_inline mm/kasan/generic.c:186 [inline]
 check_memory_region+0x141/0x190 mm/kasan/generic.c:192
 test_bit include/asm-generic/bitops/instrumented-non-atomic.h:110 [inline]
 kvm_arch_check_processor_compat+0x1f8/0x750 arch/x86/kvm/x86.c:9818
 </IRQ>
==================================================================
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 8085 Comm: syz-executor.2 Tainted: G    B             5.7.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x188/0x20d lib/dump_stack.c:118
 panic+0x2e3/0x75c kernel/panic.c:221
 end_report+0x4d/0x53 mm/kasan/report.c:104
 __kasan_report mm/kasan/report.c:520 [inline]
 kasan_report.cold+0xd/0x37 mm/kasan/report.c:530
 check_memory_region_inline mm/kasan/generic.c:186 [inline]
 check_memory_region+0x141/0x190 mm/kasan/generic.c:192
 test_bit include/asm-generic/bitops/instrumented-non-atomic.h:110 [inline]
 kvm_arch_check_processor_compat+0x1f8/0x750 arch/x86/kvm/x86.c:9818
 </IRQ>
Shutting down cpus with NMI
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

Re: KASAN: null-ptr-deref Read in kvm_arch_check_processor_compat

[Sean Christopherson]

On Tue, Jun 23, 2020 at 05:17:15AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    7ae77150 Merge tag 'powerpc-5.8-1' of git://git.kernel.org..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=135e7235100000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=d195fe572fb15312
> dashboard link: https://syzkaller.appspot.com/bug?extid=a99874f5323ce6088e53
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14d001be100000

#syz dup: general protection fault in syscall_return_slowpath