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authorSean Christopherson <seanjc@google.com>2021-09-01 13:30:26 -0700
committerPaolo Bonzini <pbonzini@redhat.com>2021-09-22 10:24:01 -0400
commit8646e53633f314e4d746a988240d3b951a92f94a (patch)
tree5815881b9c3784a7e4bfebec986b20f0840d59ea /kernel/rseq.c
parente4e737bb5c170df6135a127739a9e6148ee3da82 (diff)
KVM: rseq: Update rseq when processing NOTIFY_RESUME on xfer to KVM guest
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: 72c3c0fe54a3 ("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>
Diffstat (limited to 'kernel/rseq.c')
-rw-r--r--kernel/rseq.c14
1 files changed, 11 insertions, 3 deletions
diff --git a/kernel/rseq.c b/kernel/rseq.c
index 35f7bd0fced0..6d45ac3dae7f 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -282,9 +282,17 @@ void __rseq_handle_notify_resume(struct ksignal *ksig, struct pt_regs *regs)
if (unlikely(t->flags & PF_EXITING))
return;
- 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;