lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20230815203653.519297-16-seanjc@google.com>
Date:   Tue, 15 Aug 2023 13:36:53 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Zeng Guang <guang.zeng@...el.com>,
        Yuan Yao <yuan.yao@...el.com>
Subject: [PATCH v3 15/15] KVM: x86: Disallow guest CPUID lookups when IRQs are disabled

Now that KVM has a framework for caching guest CPUID feature flags, add
a "rule" that IRQs must be enabled when doing guest CPUID lookups, and
enforce the rule via a lockdep assertion.  CPUID lookups are slow, and
within KVM, IRQs are only ever disabled in hot paths, e.g. the core run
loop, fast page fault handling, etc.  I.e. querying guest CPUID with IRQs
disabled, especially in the run loop, should be avoided.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/cpuid.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 67e9f79fe059..e961e9a05847 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -11,6 +11,7 @@
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/kvm_host.h>
+#include "linux/lockdep.h"
 #include <linux/export.h>
 #include <linux/vmalloc.h>
 #include <linux/uaccess.h>
@@ -84,6 +85,18 @@ static inline struct kvm_cpuid_entry2 *cpuid_entry2_find(
 	struct kvm_cpuid_entry2 *e;
 	int i;
 
+	/*
+	 * KVM has a semi-arbitrary rule that querying the guest's CPUID model
+	 * with IRQs disabled is disallowed.  The CPUID model can legitimately
+	 * have over one hundred entries, i.e. the lookup is slow, and IRQs are
+	 * typically disabled in KVM only when KVM is in a performance critical
+	 * path, e.g. the core VM-Enter/VM-Exit run loop.  Nothing will break
+	 * if this rule is violated, this assertion is purely to flag potential
+	 * performance issues.  If this fires, consider moving the lookup out
+	 * of the hotpath, e.g. by caching information during CPUID updates.
+	 */
+	lockdep_assert_irqs_enabled();
+
 	for (i = 0; i < nent; i++) {
 		e = &entries[i];
 
-- 
2.41.0.694.ge786442a9b-goog

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ