linux-kernel - [PATCH 5/7] KVM: x86: Allow to update cached values in kvm_user_return

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: <20241121201448.36170-6-adrian.hunter@intel.com>
Date: Thu, 21 Nov 2024 22:14:44 +0200
From: Adrian Hunter <adrian.hunter@...el.com>
To: pbonzini@...hat.com,
	seanjc@...gle.com,
	kvm@...r.kernel.org,
	dave.hansen@...ux.intel.com
Cc: rick.p.edgecombe@...el.com,
	kai.huang@...el.com,
	adrian.hunter@...el.com,
	reinette.chatre@...el.com,
	xiaoyao.li@...el.com,
	tony.lindgren@...ux.intel.com,
	binbin.wu@...ux.intel.com,
	dmatlack@...gle.com,
	isaku.yamahata@...el.com,
	nik.borisov@...e.com,
	linux-kernel@...r.kernel.org,
	x86@...nel.org,
	yan.y.zhao@...el.com,
	chao.gao@...el.com,
	weijiang.yang@...el.com
Subject: [PATCH 5/7] KVM: x86: Allow to update cached values in kvm_user_return_msrs w/o wrmsr

From: Chao Gao <chao.gao@...el.com>

Several MSRs are constant and only used in userspace(ring 3).  But VMs may
have different values.  KVM uses kvm_set_user_return_msr() to switch to
guest's values and leverages user return notifier to restore them when the
kernel is to return to userspace.  To eliminate unnecessary wrmsr, KVM also
caches the value it wrote to an MSR last time.

TDX module unconditionally resets some of these MSRs to architectural INIT
state on TD exit.  It makes the cached values in kvm_user_return_msrs are
inconsistent with values in hardware.  This inconsistency needs to be
fixed.  Otherwise, it may mislead kvm_on_user_return() to skip restoring
some MSRs to the host's values.  kvm_set_user_return_msr() can help correct
this case, but it is not optimal as it always does a wrmsr.  So, introduce
a variation of kvm_set_user_return_msr() to update cached values and skip
that wrmsr.

Signed-off-by: Chao Gao <chao.gao@...el.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
---
TD vcpu enter/exit v1:
 - Rename functions and remove useless comment (Binbin)
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/x86.c              | 24 +++++++++++++++++++-----
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index dfa89a5d15ef..e51a95aba824 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -2303,6 +2303,7 @@ int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low,
 int kvm_add_user_return_msr(u32 msr);
 int kvm_find_user_return_msr(u32 msr);
 int kvm_set_user_return_msr(unsigned index, u64 val, u64 mask);
+void kvm_user_return_msr_update_cache(unsigned int index, u64 val);
 
 static inline bool kvm_is_supported_user_return_msr(u32 msr)
 {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 92de7ebf2cee..2b5b0ae3dd7e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -637,6 +637,15 @@ static void kvm_user_return_msr_cpu_online(void)
 	}
 }
 
+static void kvm_user_return_register_notifier(struct kvm_user_return_msrs *msrs)
+{
+	if (!msrs->registered) {
+		msrs->urn.on_user_return = kvm_on_user_return;
+		user_return_notifier_register(&msrs->urn);
+		msrs->registered = true;
+	}
+}
+
 int kvm_set_user_return_msr(unsigned slot, u64 value, u64 mask)
 {
 	struct kvm_user_return_msrs *msrs = this_cpu_ptr(user_return_msrs);
@@ -650,15 +659,20 @@ int kvm_set_user_return_msr(unsigned slot, u64 value, u64 mask)
 		return 1;
 
 	msrs->values[slot].curr = value;
-	if (!msrs->registered) {
-		msrs->urn.on_user_return = kvm_on_user_return;
-		user_return_notifier_register(&msrs->urn);
-		msrs->registered = true;
-	}
+	kvm_user_return_register_notifier(msrs);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(kvm_set_user_return_msr);
 
+void kvm_user_return_msr_update_cache(unsigned int slot, u64 value)
+{
+	struct kvm_user_return_msrs *msrs = this_cpu_ptr(user_return_msrs);
+
+	msrs->values[slot].curr = value;
+	kvm_user_return_register_notifier(msrs);
+}
+EXPORT_SYMBOL_GPL(kvm_user_return_msr_update_cache);
+
 static void drop_user_return_notifiers(void)
 {
 	struct kvm_user_return_msrs *msrs = this_cpu_ptr(user_return_msrs);
-- 
2.43.0