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 Signed-off-by: Srivatsa S. Bhat srivatsa@csail.mit.edu Reviewed-by: Matt Helsley (VMware) matt.helsley@gmail.com Reviewed-by: Alexey Makhalov amakhalov@vmware.com Reviewed-by: Bo Gan ganb@vmware.com ---

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(-)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h index f4701f0..a29edb7 100644 --- a/arch/x86/include/asm/msr-index.h +++ b/arch/x86/include/asm/msr-index.h @@ -35,6 +35,7 @@ #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 */ @@ -56,6 +57,11 @@ #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 diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 826aa81..56b84a5 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -116,7 +116,7 @@ static enum spectre_v2_mitigation spectre_v2_enabled = SPECTRE_V2_NONE;

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 __ssb_select_mitigation(void) 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, diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index eb78ddf..2f1d403 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -859,7 +859,11 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c) { 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)) @@ -871,9 +875,6 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c) 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; @@ -1216,6 +1217,7 @@ void identify_secondary_cpu(struct cpuinfo_x86 *c) enable_sep_cpu(); #endif mtrr_ap_init(); + x86_spec_ctrl_setup_ap(); }

struct msr_range { diff --git a/arch/x86/kernel/cpu/cpu.h b/arch/x86/kernel/cpu/cpu.h index 2584265..3b19d82 100644 --- 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_cpu_dev_start[],

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 */ diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c index 77d9f68..ac25d1e5 100644 --- a/arch/x86/kernel/cpu/intel.c +++ b/arch/x86/kernel/cpu/intel.c @@ -119,6 +119,7 @@ static void early_init_intel(struct cpuinfo_x86 *c) 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); }

/*