x86/speculation, KVM: Implement support for VIRT_SPEC_CTRL/LS_CFG

Add the necessary logic for supporting the emulated VIRT_SPEC_CTRL MSR to
x86_virt_spec_ctrl().  If either X86_FEATURE_LS_CFG_SSBD or
X86_FEATURE_VIRT_SPEC_CTRL is set then use the new guest_virt_spec_ctrl
argument to check whether the state must be modified on the host. The
update reuses speculative_store_bypass_update() so the ZEN-specific sibling
coordination can be reused.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
CVE-2018-3639 (x86)

(cherry-picked from commit 47c61b3955cf712cadfc25635bf9bc174af030ea)
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/arch/x86/include/asm/spec-ctrl.h b/arch/x86/include/asm/spec-ctrl.h
index c5e66980289f2ec371ccd2eeaf5a2196a65d64f1..589a940df7c6034a60b4af5815ccacf3d20619b3 100644 (file)
--- a/arch/x86/include/asm/spec-ctrl.h
+++ b/arch/x86/include/asm/spec-ctrl.h
@@ -69,6 +69,12 @@ static inline u64 ssbd_tif_to_spec_ctrl(u64 tifn)
        return (tifn & _TIF_SSBD) >> (TIF_SSBD - SPEC_CTRL_SSBD_SHIFT);
 }
 
+static inline unsigned long ssbd_spec_ctrl_to_tif(u64 spec_ctrl)
+{
+       BUILD_BUG_ON(TIF_SSBD < SPEC_CTRL_SSBD_SHIFT);
+       return (spec_ctrl & SPEC_CTRL_SSBD) << (TIF_SSBD - SPEC_CTRL_SSBD_SHIFT);
+}
+
 static inline u64 ssbd_tif_to_amd_ls_cfg(u64 tifn)
 {
        return (tifn & _TIF_SSBD) ? x86_amd_ls_cfg_ssbd_mask : 0ULL;

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 050af4672ca008aa84c61f23b162b98b18d4b52e..7e5db5aa37f30e8817298af3ef0b0399075c8cdc 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -157,6 +157,36 @@ x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bool setguest)
                        wrmsrl(MSR_IA32_SPEC_CTRL, msrval);
                }
        }
+
+       /*
+        * If SSBD is not handled in MSR_SPEC_CTRL on AMD, update
+        * MSR_AMD64_L2_CFG or MSR_VIRT_SPEC_CTRL if supported.
+        */
+       if (!static_cpu_has(X86_FEATURE_LS_CFG_SSBD) &&
+           !static_cpu_has(X86_FEATURE_VIRT_SSBD))
+               return;
+
+       /*
+        * If the host has SSBD mitigation enabled, force it in the host's
+        * virtual MSR value. If its not permanently enabled, evaluate
+        * current's TIF_SSBD thread flag.
+        */
+       if (static_cpu_has(X86_FEATURE_SPEC_STORE_BYPASS_DISABLE))
+               hostval = SPEC_CTRL_SSBD;
+       else
+               hostval = ssbd_tif_to_spec_ctrl(ti->flags);
+
+       /* Sanitize the guest value */
+       guestval = guest_virt_spec_ctrl & SPEC_CTRL_SSBD;
+
+       if (hostval != guestval) {
+               unsigned long tif;
+
+               tif = setguest ? ssbd_spec_ctrl_to_tif(guestval) :
+                                ssbd_spec_ctrl_to_tif(hostval);
+
+               speculative_store_bypass_update(tif);
+       }
 }
 EXPORT_SYMBOL_GPL(x86_virt_spec_ctrl);