diff options
Diffstat (limited to 'common/recipes-kernel/linux/linux-yocto-4.9.21/0026-KVM-x86-fix-escape-of-guest-dr6-to-the-host.patch')
-rw-r--r-- | common/recipes-kernel/linux/linux-yocto-4.9.21/0026-KVM-x86-fix-escape-of-guest-dr6-to-the-host.patch | 70 |
1 files changed, 70 insertions, 0 deletions
diff --git a/common/recipes-kernel/linux/linux-yocto-4.9.21/0026-KVM-x86-fix-escape-of-guest-dr6-to-the-host.patch b/common/recipes-kernel/linux/linux-yocto-4.9.21/0026-KVM-x86-fix-escape-of-guest-dr6-to-the-host.patch new file mode 100644 index 00000000..38255613 --- /dev/null +++ b/common/recipes-kernel/linux/linux-yocto-4.9.21/0026-KVM-x86-fix-escape-of-guest-dr6-to-the-host.patch @@ -0,0 +1,70 @@ +From 75a724909e81cd4612490d633ab269495377d332 Mon Sep 17 00:00:00 2001 +From: Wanpeng Li <wanpeng.li@hotmail.com> +Date: Wed, 13 Dec 2017 10:46:40 +0100 +Subject: [PATCH 26/33] KVM: x86: fix escape of guest dr6 to the host +MIME-Version: 1.0 +Content-Type: text/plain; charset=UTF-8 +Content-Transfer-Encoding: 8bit + +commit efdab992813fb2ed825745625b83c05032e9cda2 upstream. + +syzkaller reported: + + WARNING: CPU: 0 PID: 12927 at arch/x86/kernel/traps.c:780 do_debug+0x222/0x250 + CPU: 0 PID: 12927 Comm: syz-executor Tainted: G OE 4.15.0-rc2+ #16 + RIP: 0010:do_debug+0x222/0x250 + Call Trace: + <#DB> + debug+0x3e/0x70 + RIP: 0010:copy_user_enhanced_fast_string+0x10/0x20 + </#DB> + _copy_from_user+0x5b/0x90 + SyS_timer_create+0x33/0x80 + entry_SYSCALL_64_fastpath+0x23/0x9a + +The testcase sets a watchpoint (with perf_event_open) on a buffer that is +passed to timer_create() as the struct sigevent argument. In timer_create(), +copy_from_user()'s rep movsb triggers the BP. The testcase also sets +the debug registers for the guest. + +However, KVM only restores host debug registers when the host has active +watchpoints, which triggers a race condition when running the testcase with +multiple threads. The guest's DR6.BS bit can escape to the host before +another thread invokes timer_create(), and do_debug() complains. + +The fix is to respect do_debug()'s dr6 invariant when leaving KVM. + +Reported-by: Dmitry Vyukov <dvyukov@google.com> +Cc: Paolo Bonzini <pbonzini@redhat.com> +Cc: Radim Krčmář <rkrcmar@redhat.com> +Cc: David Hildenbrand <david@redhat.com> +Cc: Dmitry Vyukov <dvyukov@google.com> +Reviewed-by: David Hildenbrand <david@redhat.com> +Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com> +Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> +Signed-off-by: Radim Krčmář <rkrcmar@redhat.com> +Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> +--- + arch/x86/kvm/x86.c | 6 ++++++ + 1 file changed, 6 insertions(+) + +diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c +index d2ea523..af333e1 100644 +--- a/arch/x86/kvm/x86.c ++++ b/arch/x86/kvm/x86.c +@@ -2833,6 +2833,12 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) + kvm_x86_ops->vcpu_put(vcpu); + kvm_put_guest_fpu(vcpu); + vcpu->arch.last_host_tsc = rdtsc(); ++ /* ++ * If userspace has set any breakpoints or watchpoints, dr6 is restored ++ * on every vmexit, but if not, we might have a stale dr6 from the ++ * guest. do_debug expects dr6 to be cleared after it runs, do the same. ++ */ ++ set_debugreg(0, 6); + } + + static int kvm_vcpu_ioctl_get_lapic(struct kvm_vcpu *vcpu, +-- +2.7.4 + |