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Subject[PATCH 4.9 44/87] x86/bugs/intel: Set proper CPU features and setup RDS
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

commit 772439717dbf703b39990be58d8d4e3e4ad0598a upstream

Intel CPUs expose methods to:

- Detect whether RDS capability is available via CPUID.7.0.EDX[31],

- The SPEC_CTRL MSR(0x48), bit 2 set to enable RDS.

- MSR_IA32_ARCH_CAPABILITIES, Bit(4) no need to enable RRS.

With that in mind if spec_store_bypass_disable=[auto,on] is selected set at
boot-time the SPEC_CTRL MSR to enable RDS if the platform requires it.

Note that this does not fix the KVM case where the SPEC_CTRL is exposed to
guests which can muck with it, see patch titled :
KVM/SVM/VMX/x86/spectre_v2: Support the combination of guest and host IBRS.

And for the firmware (IBRS to be set), see patch titled:
x86/spectre_v2: Read SPEC_CTRL MSR during boot and re-use reserved bits

[ tglx: Distangled it from the intel implementation and kept the call order ]

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/include/asm/msr-index.h | 6 ++++++
arch/x86/kernel/cpu/bugs.c | 30 ++++++++++++++++++++++++++++--
arch/x86/kernel/cpu/common.c | 10 ++++++----
arch/x86/kernel/cpu/cpu.h | 3 +++
arch/x86/kernel/cpu/intel.c | 1 +
5 files changed, 44 insertions(+), 6 deletions(-)

--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -40,6 +40,7 @@
#define MSR_IA32_SPEC_CTRL 0x00000048 /* Speculation Control */
#define SPEC_CTRL_IBRS (1 << 0) /* Indirect Branch Restricted Speculation */
#define SPEC_CTRL_STIBP (1 << 1) /* Single Thread Indirect Branch Predictors */
+#define SPEC_CTRL_RDS (1 << 2) /* Reduced Data Speculation */

#define MSR_IA32_PRED_CMD 0x00000049 /* Prediction Command */
#define PRED_CMD_IBPB (1 << 0) /* Indirect Branch Prediction Barrier */
@@ -61,6 +62,11 @@
#define MSR_IA32_ARCH_CAPABILITIES 0x0000010a
#define ARCH_CAP_RDCL_NO (1 << 0) /* Not susceptible to Meltdown */
#define ARCH_CAP_IBRS_ALL (1 << 1) /* Enhanced IBRS support */
+#define ARCH_CAP_RDS_NO (1 << 4) /*
+ * Not susceptible to Speculative Store Bypass
+ * attack, so no Reduced Data Speculation control
+ * required.
+ */

#define MSR_IA32_BBL_CR_CTL 0x00000119
#define MSR_IA32_BBL_CR_CTL3 0x0000011e
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -116,7 +116,7 @@ static enum spectre_v2_mitigation spectr

void x86_spec_ctrl_set(u64 val)
{
- if (val & ~SPEC_CTRL_IBRS)
+ if (val & ~(SPEC_CTRL_IBRS | SPEC_CTRL_RDS))
WARN_ONCE(1, "SPEC_CTRL MSR value 0x%16llx is unknown.\n", val);
else
wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base | val);
@@ -443,8 +443,28 @@ static enum ssb_mitigation_cmd __init __
break;
}

- if (mode != SPEC_STORE_BYPASS_NONE)
+ /*
+ * We have three CPU feature flags that are in play here:
+ * - X86_BUG_SPEC_STORE_BYPASS - CPU is susceptible.
+ * - X86_FEATURE_RDS - CPU is able to turn off speculative store bypass
+ * - X86_FEATURE_SPEC_STORE_BYPASS_DISABLE - engage the mitigation
+ */
+ if (mode != SPEC_STORE_BYPASS_NONE) {
setup_force_cpu_cap(X86_FEATURE_SPEC_STORE_BYPASS_DISABLE);
+ /*
+ * Intel uses the SPEC CTRL MSR Bit(2) for this, while AMD uses
+ * a completely different MSR and bit dependent on family.
+ */
+ switch (boot_cpu_data.x86_vendor) {
+ case X86_VENDOR_INTEL:
+ x86_spec_ctrl_base |= SPEC_CTRL_RDS;
+ x86_spec_ctrl_set(SPEC_CTRL_RDS);
+ break;
+ case X86_VENDOR_AMD:
+ break;
+ }
+ }
+
return mode;
}

@@ -458,6 +478,12 @@ static void ssb_select_mitigation()

#undef pr_fmt

+void x86_spec_ctrl_setup_ap(void)
+{
+ if (boot_cpu_has(X86_FEATURE_IBRS))
+ x86_spec_ctrl_set(x86_spec_ctrl_base & (SPEC_CTRL_IBRS | SPEC_CTRL_RDS));
+}
+
#ifdef CONFIG_SYSFS

ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr,
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -903,7 +903,11 @@ static void __init cpu_set_bug_bits(stru
{
u64 ia32_cap = 0;

- if (!x86_match_cpu(cpu_no_spec_store_bypass))
+ if (cpu_has(c, X86_FEATURE_ARCH_CAPABILITIES))
+ rdmsrl(MSR_IA32_ARCH_CAPABILITIES, ia32_cap);
+
+ if (!x86_match_cpu(cpu_no_spec_store_bypass) &&
+ !(ia32_cap & ARCH_CAP_RDS_NO))
setup_force_cpu_bug(X86_BUG_SPEC_STORE_BYPASS);

if (x86_match_cpu(cpu_no_speculation))
@@ -915,9 +919,6 @@ static void __init cpu_set_bug_bits(stru
if (x86_match_cpu(cpu_no_meltdown))
return;

- if (cpu_has(c, X86_FEATURE_ARCH_CAPABILITIES))
- rdmsrl(MSR_IA32_ARCH_CAPABILITIES, ia32_cap);
-
/* Rogue Data Cache Load? No! */
if (ia32_cap & ARCH_CAP_RDCL_NO)
return;
@@ -1339,6 +1340,7 @@ void identify_secondary_cpu(struct cpuin
#endif
mtrr_ap_init();
validate_apic_and_package_id(c);
+ x86_spec_ctrl_setup_ap();
}

struct msr_range {
--- a/arch/x86/kernel/cpu/cpu.h
+++ b/arch/x86/kernel/cpu/cpu.h
@@ -46,4 +46,7 @@ extern const struct cpu_dev *const __x86

extern void get_cpu_cap(struct cpuinfo_x86 *c);
extern void cpu_detect_cache_sizes(struct cpuinfo_x86 *c);
+
+extern void x86_spec_ctrl_setup_ap(void);
+
#endif /* ARCH_X86_CPU_H */
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -154,6 +154,7 @@ static void early_init_intel(struct cpui
setup_clear_cpu_cap(X86_FEATURE_STIBP);
setup_clear_cpu_cap(X86_FEATURE_SPEC_CTRL);
setup_clear_cpu_cap(X86_FEATURE_INTEL_STIBP);
+ setup_clear_cpu_cap(X86_FEATURE_RDS);
}

/*

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