From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
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.
[ bp: Massage. ]
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx>
---
arch/x86/include/asm/cpufeatures.h | 1 +
arch/x86/kernel/cpu/amd.c | 21 +++++++++++++++------
arch/x86/kernel/cpu/common.c | 6 ++++--
3 files changed, 20 insertions(+), 8 deletions(-)
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 611efccdc742..d6fc05367439 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -304,6 +304,7 @@
#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 88cef978380b..5571b28d35b6 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -894,12 +894,21 @@ static void init_amd_zn(struct cpuinfo_x86 *c)
node_reclaim_distance = 32;
#endif
- /*
- * 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 4035581f61e0..0002dc62214d 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1259,8 +1259,10 @@ 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;
--
2.34.1
