x86/cpu/amd: Enumerate BTC_NO

commit 26aae8ccbc1972233afd08fb3f368947c0314265 upstream.

BTC_NO indicates that hardware is not susceptible to Branch Type Confusion.

Zen3 CPUs don't suffer BTC.

Hypervisors are expected to synthesise BTC_NO when it is appropriate
given the migration pool, to prevent kernels using heuristics.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
[ bp: Adjust context ]
Signed-off-by: Suraj Jitindar Singh <surajjs@amazon.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 fc52b59c317871180e1241f1d4806e5041b0ca44..c01cc52a928547fa90842a2f4693a143190ff9d2 100644 (file)
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -303,6 +303,7 @@
 #define X86_FEATURE_AMD_SSBD           (13*32+24) /* "" Speculative Store Bypass Disable */
 #define X86_FEATURE_VIRT_SSBD          (13*32+25) /* Virtualized Speculative Store Bypass Disable */
 #define X86_FEATURE_AMD_SSB_NO         (13*32+26) /* "" Speculative Store Bypass is fixed in hardware. */
+#define X86_FEATURE_BTC_NO             (13*32+29) /* "" Not vulnerable to Branch Type Confusion */
 
 /* Thermal and Power Management Leaf, CPUID level 0x00000006 (EAX), word 14 */
 #define X86_FEATURE_DTHERM             (14*32+ 0) /* Digital Thermal Sensor */

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 3914f9218a6bcfc131ef34189fe1654a2a79338e..0ccd74d37aad732a30348b26b3d93d318c8d4679 100644 (file)
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -857,12 +857,21 @@ static void init_amd_zn(struct cpuinfo_x86 *c)
 {
        set_cpu_cap(c, X86_FEATURE_ZEN);
 
-       /*
-        * Fix erratum 1076: CPB feature bit not being set in CPUID.
-        * Always set it, except when running under a hypervisor.
-        */
-       if (!cpu_has(c, X86_FEATURE_HYPERVISOR) && !cpu_has(c, X86_FEATURE_CPB))
-               set_cpu_cap(c, X86_FEATURE_CPB);
+       /* Fix up CPUID bits, but only if not virtualised. */
+       if (!cpu_has(c, X86_FEATURE_HYPERVISOR)) {
+
+               /* Erratum 1076: CPB feature bit not being set in CPUID. */
+               if (!cpu_has(c, X86_FEATURE_CPB))
+                       set_cpu_cap(c, X86_FEATURE_CPB);
+
+               /*
+                * Zen3 (Fam19 model < 0x10) parts are not susceptible to
+                * Branch Type Confusion, but predate the allocation of the
+                * BTC_NO bit.
+                */
+               if (c->x86 == 0x19 && !cpu_has(c, X86_FEATURE_BTC_NO))
+                       set_cpu_cap(c, X86_FEATURE_BTC_NO);
+       }
 }
 
 static void init_amd(struct cpuinfo_x86 *c)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 67eefcb7f9250fb5ed4aab9790eff9071a3ebf6e..44562885fa1d6278e8202c2769626066c8f3cda7 100644 (file)
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1123,8 +1123,10 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
                        setup_force_cpu_bug(X86_BUG_MMIO_UNKNOWN);
        }
 
-       if ((cpu_matches(cpu_vuln_blacklist, RETBLEED) || (ia32_cap & ARCH_CAP_RSBA)))
-               setup_force_cpu_bug(X86_BUG_RETBLEED);
+       if (!cpu_has(c, X86_FEATURE_BTC_NO)) {
+               if (cpu_matches(cpu_vuln_blacklist, RETBLEED) || (ia32_cap & ARCH_CAP_RSBA))
+                       setup_force_cpu_bug(X86_BUG_RETBLEED);
+       }
 
        if (cpu_matches(cpu_vuln_whitelist, NO_MELTDOWN))
                return;