x86/cpufeatures: Disentangle MSR_SPEC_CTRL enumeration from IBRS

commit 7eb8956a7fec3c1f0abc2a5517dada99ccc8a961 upstream

The availability of the SPEC_CTRL MSR is enumerated by a CPUID bit on
Intel and implied by IBRS or STIBP support on AMD. That's just confusing
and in case an AMD CPU has IBRS not supported because the underlying
problem has been fixed but has another bit valid in the SPEC_CTRL MSR,
the thing falls apart.

Add a synthetic feature bit X86_FEATURE_MSR_SPEC_CTRL to denote the
availability on both Intel and AMD.

While at it replace the boot_cpu_has() checks with static_cpu_has() where
possible. This prevents late microcode loading from exposing SPEC_CTRL, but
late loading is already very limited as it does not reevaluate the
mitigation options and other bits and pieces. Having static_cpu_has() is
the simplest and least fragile solution.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index ecfeb9249637f32ce9a9d4a6c67852f799e93110..62a8badac6afa46b96af4bc6907348cd5ee0ca01 100644 (file)
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -206,6 +206,8 @@
 #define X86_FEATURE_RETPOLINE_AMD      ( 7*32+13) /* "" AMD Retpoline mitigation for Spectre variant 2 */
 #define X86_FEATURE_INTEL_PPIN         ( 7*32+14) /* Intel Processor Inventory Number */
 
+#define X86_FEATURE_MSR_SPEC_CTRL      ( 7*32+16) /* "" MSR SPEC_CTRL is implemented */
+
 #define X86_FEATURE_MBA                        ( 7*32+18) /* Memory Bandwidth Allocation */
 #define X86_FEATURE_RSB_CTXSW          ( 7*32+19) /* "" Fill RSB on context switches */
 

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index bab05913f86411933e62207035f5d9fcd9ab9154..316cb24092a3030a7880bdae98cdb9449951427a 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -64,7 +64,7 @@ void __init check_bugs(void)
         * have unknown values. AMD64_LS_CFG MSR is cached in the early AMD
         * init code as it is not enumerated and depends on the family.
         */
-       if (boot_cpu_has(X86_FEATURE_IBRS))
+       if (boot_cpu_has(X86_FEATURE_MSR_SPEC_CTRL))
                rdmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
 
        /* Select the proper spectre mitigation before patching alternatives */
@@ -145,7 +145,7 @@ u64 x86_spec_ctrl_get_default(void)
 {
        u64 msrval = x86_spec_ctrl_base;
 
-       if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL)
+       if (static_cpu_has(X86_FEATURE_SPEC_CTRL))
                msrval |= ssbd_tif_to_spec_ctrl(current_thread_info()->flags);
        return msrval;
 }
@@ -155,10 +155,12 @@ void x86_spec_ctrl_set_guest(u64 guest_spec_ctrl)
 {
        u64 host = x86_spec_ctrl_base;
 
-       if (!boot_cpu_has(X86_FEATURE_IBRS))
+       /* Is MSR_SPEC_CTRL implemented ? */
+       if (!static_cpu_has(X86_FEATURE_MSR_SPEC_CTRL))
                return;
 
-       if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL)
+       /* Intel controls SSB in MSR_SPEC_CTRL */
+       if (static_cpu_has(X86_FEATURE_SPEC_CTRL))
                host |= ssbd_tif_to_spec_ctrl(current_thread_info()->flags);
 
        if (host != guest_spec_ctrl)
@@ -170,10 +172,12 @@ void x86_spec_ctrl_restore_host(u64 guest_spec_ctrl)
 {
        u64 host = x86_spec_ctrl_base;
 
-       if (!boot_cpu_has(X86_FEATURE_IBRS))
+       /* Is MSR_SPEC_CTRL implemented ? */
+       if (!static_cpu_has(X86_FEATURE_MSR_SPEC_CTRL))
                return;
 
-       if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL)
+       /* Intel controls SSB in MSR_SPEC_CTRL */
+       if (static_cpu_has(X86_FEATURE_SPEC_CTRL))
                host |= ssbd_tif_to_spec_ctrl(current_thread_info()->flags);
 
        if (host != guest_spec_ctrl)
@@ -631,7 +635,7 @@ int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which)
 
 void x86_spec_ctrl_setup_ap(void)
 {
-       if (boot_cpu_has(X86_FEATURE_IBRS))
+       if (boot_cpu_has(X86_FEATURE_MSR_SPEC_CTRL))
                x86_spec_ctrl_set(x86_spec_ctrl_base & ~x86_spec_ctrl_mask);
 
        if (ssb_mode == SPEC_STORE_BYPASS_DISABLE)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 8ff004d6e184eeb3c40f47bcd08836bec210c1ba..7a4fed3f7ae5af7e71fbfc2a513f0707f9ab3644 100644 (file)
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -737,19 +737,24 @@ static void init_speculation_control(struct cpuinfo_x86 *c)
        if (cpu_has(c, X86_FEATURE_SPEC_CTRL)) {
                set_cpu_cap(c, X86_FEATURE_IBRS);
                set_cpu_cap(c, X86_FEATURE_IBPB);
+               set_cpu_cap(c, X86_FEATURE_MSR_SPEC_CTRL);
        }
 
        if (cpu_has(c, X86_FEATURE_INTEL_STIBP))
                set_cpu_cap(c, X86_FEATURE_STIBP);
 
-       if (cpu_has(c, X86_FEATURE_AMD_IBRS))
+       if (cpu_has(c, X86_FEATURE_AMD_IBRS)) {
                set_cpu_cap(c, X86_FEATURE_IBRS);
+               set_cpu_cap(c, X86_FEATURE_MSR_SPEC_CTRL);
+       }
 
        if (cpu_has(c, X86_FEATURE_AMD_IBPB))
                set_cpu_cap(c, X86_FEATURE_IBPB);
 
-       if (cpu_has(c, X86_FEATURE_AMD_STIBP))
+       if (cpu_has(c, X86_FEATURE_AMD_STIBP)) {
                set_cpu_cap(c, X86_FEATURE_STIBP);
+               set_cpu_cap(c, X86_FEATURE_MSR_SPEC_CTRL);
+       }
 }
 
 void get_cpu_cap(struct cpuinfo_x86 *c)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index ae117667d559dd3c2549bcaf328bc1c93603b25a..f11c39bbb1f0e1f2d9168333d56add92ae0e203f 100644 (file)
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -188,6 +188,7 @@ static void early_init_intel(struct cpuinfo_x86 *c)
                setup_clear_cpu_cap(X86_FEATURE_IBPB);
                setup_clear_cpu_cap(X86_FEATURE_STIBP);
                setup_clear_cpu_cap(X86_FEATURE_SPEC_CTRL);
+               setup_clear_cpu_cap(X86_FEATURE_MSR_SPEC_CTRL);
                setup_clear_cpu_cap(X86_FEATURE_INTEL_STIBP);
                setup_clear_cpu_cap(X86_FEATURE_SSBD);
        }