From 9eb04f65fa5bc29a04d6bd9930b04d1e088604bb Mon Sep 17 00:00:00 2001
From: Sean Christopherson <seanjc@google.com>
Date: Mon, 25 Oct 2021 13:13:10 -0700
Subject: [PATCH 1/2] KVM: x86: Don't WARN if userspace mucks with RCX during
string I/O exit
Git-commit: d07898eaf39909806128caccb6ebd922ee3edd69
Patch-mainline: v5.16-rc5
References: bsc#1194298
Replace a WARN with a comment to call out that userspace can modify RCX
during an exit to userspace to handle string I/O. KVM doesn't actually
support changing the rep count during an exit, i.e. the scenario can be
ignored, but the WARN needs to go as it's trivial to trigger from
userspace.
Cc: stable@vger.kernel.org
Fixes: 3b27de271839 ("KVM: x86: split the two parts of emulator_pio_in")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211025201311.1881846-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Li Zhang <lizhang@suse.de>
---
arch/x86/kvm/x86.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d0a01cb62ae2..27ff04ea9eba 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6883,7 +6883,13 @@ static int emulator_pio_in(struct kvm_vcpu *vcpu, int size,
unsigned short port, void *val, unsigned int count)
{
if (vcpu->arch.pio.count) {
- /* Complete previous iteration. */
+ /*
+ * Complete a previous iteration that required userspace I/O.
+ * Note, @count isn't guaranteed to match pio.count as userspace
+ * can modify ECX before rerunning the vCPU. Ignore any such
+ * shenanigans as KVM doesn't support modifying the rep count,
+ * and the emulator ensures @count doesn't overflow the buffer.
+ */
} else {
int r = __emulator_pio_in(vcpu, size, port, count);
if (!r)
@@ -6892,7 +6898,6 @@ static int emulator_pio_in(struct kvm_vcpu *vcpu, int size,
/* Results already available, fall through. */
}
- WARN_ON(count != vcpu->arch.pio.count);
complete_emulator_pio_in(vcpu, val);
return 1;
}
--
2.31.1