This is a note to let you know that I've just added the patch titled
KVM: X86: Disable hardware breakpoints unconditionally before kvm_x86->run()
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
kvm-x86-disable-hardware-breakpoints-unconditionally-before-kvm_x86-run.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From f85d40160691881a17a397c448d799dfc90987ba Mon Sep 17 00:00:00 2001
From: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
Date: Tue, 29 Jun 2021 01:26:32 +0800
Subject: KVM: X86: Disable hardware breakpoints unconditionally before kvm_x86->run()
From: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
commit f85d40160691881a17a397c448d799dfc90987ba upstream.
When the host is using debug registers but the guest is not using them
nor is the guest in guest-debug state, the kvm code does not reset
the host debug registers before kvm_x86->run(). Rather, it relies on
the hardware vmentry instruction to automatically reset the dr7 registers
which ensures that the host breakpoints do not affect the guest.
This however violates the non-instrumentable nature around VM entry
and exit; for example, when a host breakpoint is set on vcpu->arch.cr2,
Another issue is consistency. When the guest debug registers are active,
the host breakpoints are reset before kvm_x86->run(). But when the
guest debug registers are inactive, the host breakpoints are delayed to
be disabled. The host tracing tools may see different results depending
on what the guest is doing.
To fix the problems, we clear %db7 unconditionally before kvm_x86->run()
if the host has set any breakpoints, no matter if the guest is using
them or not.
Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
Message-Id: <20210628172632.81029-1-jiangshanlai@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
[Only clear %db7 instead of reloading all debug registers. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kvm/x86.c | 2 ++
1 file changed, 2 insertions(+)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7044,6 +7044,8 @@ static int vcpu_enter_guest(struct kvm_v
set_debugreg(vcpu->arch.eff_db[3], 3);
set_debugreg(vcpu->arch.dr6, 6);
vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_RELOAD;
+ } else if (unlikely(hw_breakpoint_active())) {
+ set_debugreg(0, 7);
}
kvm_x86_ops->run(vcpu);
Patches currently in stable-queue which might be from laijs@xxxxxxxxxxxxxxxxx are
queue-4.9/kvm-x86-disable-hardware-breakpoints-unconditionally-before-kvm_x86-run.patch
