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KVM: rseq: Update rseq when processing NOTIFY_RESUME on xfer to KVM guest

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commit 8646e53633 upstream.

Invoke rseq's NOTIFY_RESUME handler when processing the flag prior to
transferring to a KVM guest, which is roughly equivalent to an exit to
userspace and processes many of the same pending actions.  While the task
cannot be in an rseq critical section as the KVM path is reachable only
by via ioctl(KVM_RUN), the side effects that apply to rseq outside of a
critical section still apply, e.g. the current CPU needs to be updated if
the task is migrated.

Clearing TIF_NOTIFY_RESUME without informing rseq can lead to segfaults
and other badness in userspace VMMs that use rseq in combination with KVM,
e.g. due to the CPU ID being stale after task migration.

Fixes: 72c3c0fe54 ("x86/kvm: Use generic xfer to guest work function")
Reported-by: Peter Foley <pefoley@google.com>
Bisected-by: Doug Evans <dje@google.com>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210901203030.1292304-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[sean: Resolve benign conflict due to unrelated access_ok() check in 5.10]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Sean Christopherson 2021-09-01 13:30:26 -07:00 committed by Greg Kroah-Hartman
parent 3778511dfc
commit 249e5e5a50
2 changed files with 13 additions and 4 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

4
kernel/entry/kvm.c
View file

@ -16,8 +16,10 @@ static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work)
if (ti_work & _TIF_NEED_RESCHED)
schedule();
if (ti_work & _TIF_NOTIFY_RESUME)
if (ti_work & _TIF_NOTIFY_RESUME) {
tracehook_notify_resume(NULL);
rseq_handle_notify_resume(NULL, NULL);
}
ret = arch_xfer_to_guest_mode_handle_work(vcpu, ti_work);
if (ret)

13
kernel/rseq.c
View file

@ -268,9 +268,16 @@ void __rseq_handle_notify_resume(struct ksignal *ksig, struct pt_regs *regs)
return;
if (unlikely(!access_ok(t->rseq, sizeof(*t->rseq))))
goto error;
ret = rseq_ip_fixup(regs);
if (unlikely(ret < 0))
goto error;
/*
* regs is NULL if and only if the caller is in a syscall path. Skip
* fixup and leave rseq_cs as is so that rseq_sycall() will detect and
* kill a misbehaving userspace on debug kernels.
*/
if (regs) {
ret = rseq_ip_fixup(regs);
if (unlikely(ret < 0))
goto error;
}
if (unlikely(rseq_update_cpu_id(t)))
goto error;
return;