linux-kernel - [PATCH v3 19/27] KVM: x86: Allow FRED/LKGS to be advertised to guests

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: <20241001050110.3643764-20-xin@zytor.com>
Date: Mon, 30 Sep 2024 22:01:02 -0700
From: "Xin Li (Intel)" <xin@...or.com>
To: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org
Cc: seanjc@...gle.com, pbonzini@...hat.com, corbet@....net, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, luto@...nel.org, peterz@...radead.org,
        andrew.cooper3@...rix.com, xin@...or.com
Subject: [PATCH v3 19/27] KVM: x86: Allow FRED/LKGS to be advertised to guests

From: Xin Li <xin3.li@...el.com>

Allow FRED/LKGS to be advertised to guests after changes required to
enable FRED in a KVM guest are in place.

LKGS is introduced with FRED to completely eliminate the need to swapgs
explicilty, because

1) FRED transitions ensure that an operating system can always operate
   with its own GS base address.

2) LKGS behaves like the MOV to GS instruction except that it loads
   the base address into the IA32_KERNEL_GS_BASE MSR instead of the
   GS segment’s descriptor cache, which is exactly what Linux kernel
   does to load a user level GS base.  Thus there is no need to SWAPGS
   away from the kernel GS base and an execution of SWAPGS causes #UD
   if FRED transitions are enabled.

A FRED CPU must enumerate LKGS.  When LKGS is not available, FRED must
not be enabled.

Signed-off-by: Xin Li <xin3.li@...el.com>
Signed-off-by: Xin Li (Intel) <xin@...or.com>
Tested-by: Shan Kang <shan.kang@...el.com>
---
 arch/x86/kvm/cpuid.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 41786b834b16..c55d150ece8d 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -699,7 +699,7 @@ void kvm_set_cpu_caps(void)

 	kvm_cpu_cap_mask(CPUID_7_1_EAX,
 		F(AVX_VNNI) | F(AVX512_BF16) | F(CMPCCXADD) |
-		F(FZRM) | F(FSRS) | F(FSRC) |
+		F(FZRM) | F(FSRS) | F(FSRC) | F(FRED) | F(LKGS) |
 		F(AMX_FP16) | F(AVX_IFMA) | F(LAM)
 	);

-- 
2.46.2