x86: introduce and use setup_force_cpu_cap()

For XEN_SMEP and XEN_SMAP to not be cleared while bringing up APs we'd
need to clone the respective hack used for CPUID_FAULTING. Introduce an
inverse of setup_clear_cpu_cap() instead, but let clearing of features
overrule forced setting of them.

XEN_SMAP being wrong post-boot is a problem specifically for live
patching, as a live patch may need alternative instruction patching
keyed off of that feature flag.

Reported-by: Sarah Newman <security@prgmr.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

diff --git a/xen/arch/x86/apic.c b/xen/arch/x86/apic.c
index 2638414e08d0e94566bbbd358e07fe197d78928a..ed59440c4560487a1cebc67738953b396497f6f6 100644 (file)
--- a/xen/arch/x86/apic.c
+++ b/xen/arch/x86/apic.c
@@ -853,7 +853,7 @@ static int __init detect_init_APIC (void)
         return -1;
     }
 
-    __set_bit(X86_FEATURE_APIC, boot_cpu_data.x86_capability);
+    setup_force_cpu_cap(X86_FEATURE_APIC);
     mp_lapic_addr = APIC_DEFAULT_PHYS_BASE;
 
     /* The BIOS may have set up the APIC at some other address */

diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index 2fdc2f98aabe696e206bf1bfe342cac936be8257..78f56671e7e6879fa3aaef9a756c644644dc775d 100644 (file)
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -54,6 +54,7 @@ unsigned int vaddr_bits __read_mostly = VADDR_BITS;
 u64 host_pat = 0x050100070406;
 
 static unsigned int cleared_caps[NCAPINTS];
+static unsigned int forced_caps[NCAPINTS];
 
 void __init setup_clear_cpu_cap(unsigned int cap)
 {
@@ -63,6 +64,10 @@ void __init setup_clear_cpu_cap(unsigned int cap)
        if (__test_and_set_bit(cap, cleared_caps))
                return;
 
+       if (test_bit(cap, forced_caps))
+               printk("%pS clearing previously forced feature %#x\n",
+                      __builtin_return_address(0), cap);
+
        __clear_bit(cap, boot_cpu_data.x86_capability);
        dfs = lookup_deep_deps(cap);
 
@@ -72,9 +77,28 @@ void __init setup_clear_cpu_cap(unsigned int cap)
        for (i = 0; i < FSCAPINTS; ++i) {
                cleared_caps[i] |= dfs[i];
                boot_cpu_data.x86_capability[i] &= ~dfs[i];
+               if (!(forced_caps[i] & dfs[i]))
+                       continue;
+               printk("%pS implicitly clearing previously forced feature(s) %u:%#x\n",
+                      __builtin_return_address(0),
+                      i, forced_caps[i] & dfs[i]);
        }
 }
 
+void __init setup_force_cpu_cap(unsigned int cap)
+{
+       if (__test_and_set_bit(cap, forced_caps))
+               return;
+
+       if (test_bit(cap, cleared_caps)) {
+               printk("%pS tries to force previously cleared feature %#x\n",
+                      __builtin_return_address(0), cap);
+               return;
+       }
+
+       __set_bit(cap, boot_cpu_data.x86_capability);
+}
+
 static void default_init(struct cpuinfo_x86 * c)
 {
        /* Not much we can do here... */
@@ -375,8 +399,10 @@ void identify_cpu(struct cpuinfo_x86 *c)
        for (i = 0; i < FSCAPINTS; ++i)
                c->x86_capability[i] &= known_features[i];
 
-       for (i = 0 ; i < NCAPINTS ; ++i)
+       for (i = 0 ; i < NCAPINTS ; ++i) {
+               c->x86_capability[i] |= forced_caps[i];
                c->x86_capability[i] &= ~cleared_caps[i];
+       }
 
        /* If the model name is still unset, do table lookup. */
        if ( !c->x86_model_id[0] ) {

diff --git a/xen/arch/x86/cpu/intel.c b/xen/arch/x86/cpu/intel.c
index 2e2032756930c8c43676917380ab53dc7740d6bd..6a4133416808cc1de16270df33eecb0277d0d168 100644 (file)
--- a/xen/arch/x86/cpu/intel.c
+++ b/xen/arch/x86/cpu/intel.c
@@ -27,7 +27,7 @@ static bool __init probe_intel_cpuid_faulting(void)
 
        expected_levelling_cap |= LCAP_faulting;
        levelling_caps |=  LCAP_faulting;
-       __set_bit(X86_FEATURE_CPUID_FAULTING, boot_cpu_data.x86_capability);
+       setup_force_cpu_cap(X86_FEATURE_CPUID_FAULTING);
        return 1;
 }
 
@@ -320,9 +320,6 @@ static void early_init_intel(struct cpuinfo_x86 *c)
        if (c == &boot_cpu_data)
                intel_init_levelling();
 
-       if (test_bit(X86_FEATURE_CPUID_FAULTING, boot_cpu_data.x86_capability))
-               __set_bit(X86_FEATURE_CPUID_FAULTING, c->x86_capability);
-
        intel_ctxt_switch_levelling(NULL);
 }
 

diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index bc466e8a8ec14d0979e083ce91615e07f11d43bb..3cbe305202e5682c5b356533fbe7c82597f45624 100644 (file)
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -1485,14 +1485,14 @@ void __init noreturn __start_xen(unsigned long mbi_p)
     if ( !opt_smep )
         setup_clear_cpu_cap(X86_FEATURE_SMEP);
     if ( cpu_has_smep && opt_smep != SMEP_HVM_ONLY )
-        __set_bit(X86_FEATURE_XEN_SMEP, boot_cpu_data.x86_capability);
+        setup_force_cpu_cap(X86_FEATURE_XEN_SMEP);
     if ( boot_cpu_has(X86_FEATURE_XEN_SMEP) )
         set_in_cr4(X86_CR4_SMEP);
 
     if ( !opt_smap )
         setup_clear_cpu_cap(X86_FEATURE_SMAP);
     if ( cpu_has_smap && opt_smap != SMAP_HVM_ONLY )
-        __set_bit(X86_FEATURE_XEN_SMAP, boot_cpu_data.x86_capability);
+        setup_force_cpu_cap(X86_FEATURE_XEN_SMAP);
     if ( boot_cpu_has(X86_FEATURE_XEN_SMAP) )
         set_in_cr4(X86_CR4_SMAP);
 

diff --git a/xen/include/asm-x86/processor.h b/xen/include/asm-x86/processor.h
index 4bef69863384fbc45f21e91fdcd3a9eddc53357a..8b39fb4be9868ff3ecda12b2e0d85f4d3e1e1730 100644 (file)
--- a/xen/include/asm-x86/processor.h
+++ b/xen/include/asm-x86/processor.h
@@ -169,6 +169,7 @@ extern const struct x86_cpu_id *x86_match_cpu(const struct x86_cpu_id table[]);
 
 extern void identify_cpu(struct cpuinfo_x86 *);
 extern void setup_clear_cpu_cap(unsigned int);
+extern void setup_force_cpu_cap(unsigned int);
 extern void print_cpu_info(unsigned int cpu);
 extern unsigned int init_intel_cacheinfo(struct cpuinfo_x86 *c);