linux-kernel - [PATCH v3 53/57] KVM: x86: Pull CPUID capabilities from boot_cpu

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: <20241128013424.4096668-54-seanjc@google.com>
Date: Wed, 27 Nov 2024 17:34:20 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <seanjc@...gle.com>, 
	Vitaly Kuznetsov <vkuznets@...hat.com>, Jarkko Sakkinen <jarkko@...nel.org>
Cc: kvm@...r.kernel.org, linux-sgx@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Maxim Levitsky <mlevitsk@...hat.com>, 
	Hou Wenlong <houwenlong.hwl@...group.com>, Xiaoyao Li <xiaoyao.li@...el.com>, 
	Kechen Lu <kechenl@...dia.com>, Oliver Upton <oliver.upton@...ux.dev>, 
	Binbin Wu <binbin.wu@...ux.intel.com>, Yang Weijiang <weijiang.yang@...el.com>, 
	Robert Hoo <robert.hoo.linux@...il.com>
Subject: [PATCH v3 53/57] KVM: x86: Pull CPUID capabilities from boot_cpu_data
 only as needed

Don't memcpy() all of boot_cpu_data.x86_capability, and instead explicitly
fill each kvm_cpu_cap_init leaf during kvm_cpu_cap_init().  While clever,
copying all kernel capabilities risks over-reporting KVM capabilities,
e.g. if KVM added support in __do_cpuid_func(), but neglected to init the
supported set of capabilities.

Note, explicitly grabbing leafs deliberately keeps Linux-defined leafs as
0!  KVM should never advertise Linux-defined leafs; any relevant features
that are "real", but scattered, must be gathered in their correct hardware-
defined leaf.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/cpuid.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 2b05a7e61994..3b8ec5e7e39a 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -657,21 +657,23 @@ static __always_inline u32 raw_cpuid_get(struct cpuid_reg cpuid)
 }
 
 /*
- * For kernel-defined leafs, mask the boot CPU's pre-populated value.  For KVM-
- * defined leafs, explicitly set the leaf, as KVM is the one and only authority.
+ * For kernel-defined leafs, mask KVM's supported feature set with the kernel's
+ * capabilities as well as raw CPUID.  For KVM-defined leafs, consult only raw
+ * CPUID, as KVM is the one and only authority (in the kernel).
  */
 #define kvm_cpu_cap_init(leaf, mask)					\
 do {									\
 	const struct cpuid_reg cpuid = x86_feature_cpuid(leaf * 32);	\
 	const u32 __maybe_unused kvm_cpu_cap_init_in_progress = leaf;	\
+	const u32 *kernel_cpu_caps = boot_cpu_data.x86_capability;	\
 	u32 kvm_cpu_cap_passthrough = 0;				\
 	u32 kvm_cpu_cap_synthesized = 0;				\
 	u32 kvm_cpu_cap_emulated = 0;					\
 									\
+	kvm_cpu_caps[leaf] = (mask);					\
+									\
 	if (leaf < NCAPINTS)						\
-		kvm_cpu_caps[leaf] &= (mask);				\
-	else								\
-		kvm_cpu_caps[leaf] = (mask);				\
+		kvm_cpu_caps[leaf] &= kernel_cpu_caps[leaf];		\
 									\
 	kvm_cpu_caps[leaf] |= kvm_cpu_cap_passthrough;			\
 	kvm_cpu_caps[leaf] &= (raw_cpuid_get(cpuid) |			\
@@ -769,9 +771,6 @@ void kvm_set_cpu_caps(void)
 	BUILD_BUG_ON(sizeof(kvm_cpu_caps) - (NKVMCAPINTS * sizeof(*kvm_cpu_caps)) >
 		     sizeof(boot_cpu_data.x86_capability));
 
-	memcpy(&kvm_cpu_caps, &boot_cpu_data.x86_capability,
-	       sizeof(kvm_cpu_caps) - (NKVMCAPINTS * sizeof(*kvm_cpu_caps)));
-
 	kvm_cpu_cap_init(CPUID_1_ECX,
 		F(XMM3) |
 		F(PCLMULQDQ) |
-- 
2.47.0.338.g60cca15819-goog