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Commit 6ac2f49e authored by Konrad Rzeszutek Wilk's avatar Konrad Rzeszutek Wilk Committed by Thomas Gleixner
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x86/bugs: Add AMD's SPEC_CTRL MSR usage 

The AMD document outlining the SSBD handling
124441_AMD64_SpeculativeStoreBypassDisable_Whitepaper_final.pdf
mentions that if CPUID 8000_0008.EBX[24] is set we should be using
the SPEC_CTRL MSR (0x48) over the VIRT SPEC_CTRL MSR (0xC001_011f)
for speculative store bypass disable.

This in effect means we should clear the X86_FEATURE_VIRT_SSBD
flag so that we would prefer the SPEC_CTRL MSR.

See the document titled:
   124441_AMD64_SpeculativeStoreBypassDisable_Whitepaper_final.pdf

A copy of this document is available at
   https://bugzilla.kernel.org/show_bug.cgi?id=199889



Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>
Cc: kvm@vger.kernel.org
Cc: KarimAllah Ahmed <karahmed@amazon.de>
Cc: andrew.cooper3@citrix.com
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20180601145921.9500-3-konrad.wilk@oracle.com
parent 24809860

arch/x86/include/asm/cpufeatures.h

+1 −0
Original line number Diff line number Diff line
@@ -282,6 +282,7 @@ 
#define X86_FEATURE_AMD_IBPB		(13*32+12) /* "" Indirect Branch Prediction Barrier */

#define X86_FEATURE_AMD_IBRS		(13*32+14) /* "" Indirect Branch Restricted Speculation */

#define X86_FEATURE_AMD_STIBP		(13*32+15) /* "" Single Thread Indirect Branch Predictors */

#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. */

arch/x86/kernel/cpu/bugs.c

+7 −5
Original line number Diff line number Diff line
@@ -529,18 +529,20 @@ static enum ssb_mitigation __init __ssb_select_mitigation(void) 
	if (mode == SPEC_STORE_BYPASS_DISABLE) {

		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.

		 * Intel uses the SPEC CTRL MSR Bit(2) for this, while AMD may

		 * use a completely different MSR and bit dependent on family.

		 */

		switch (boot_cpu_data.x86_vendor) {

		case X86_VENDOR_INTEL:

		case X86_VENDOR_AMD:

			if (!static_cpu_has(X86_FEATURE_MSR_SPEC_CTRL)) {

				x86_amd_ssb_disable();

				break;

			}

			x86_spec_ctrl_base |= SPEC_CTRL_SSBD;

			x86_spec_ctrl_mask |= SPEC_CTRL_SSBD;

			wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);

			break;

		case X86_VENDOR_AMD:

			x86_amd_ssb_disable();

			break;

		}

	}

arch/x86/kernel/cpu/common.c

+6 −0
Original line number Diff line number Diff line
@@ -803,6 +803,12 @@ static void init_speculation_control(struct cpuinfo_x86 *c) 
		set_cpu_cap(c, X86_FEATURE_STIBP);

		set_cpu_cap(c, X86_FEATURE_MSR_SPEC_CTRL);

	}



	if (cpu_has(c, X86_FEATURE_AMD_SSBD)) {

		set_cpu_cap(c, X86_FEATURE_SSBD);

		set_cpu_cap(c, X86_FEATURE_MSR_SPEC_CTRL);

		clear_cpu_cap(c, X86_FEATURE_VIRT_SSBD);

	}

}



void get_cpu_cap(struct cpuinfo_x86 *c)

arch/x86/kvm/cpuid.c

+8 −2
Original line number Diff line number Diff line
@@ -379,7 +379,8 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function, 


	/* cpuid 0x80000008.ebx */

	const u32 kvm_cpuid_8000_0008_ebx_x86_features =

		F(AMD_IBPB) | F(AMD_IBRS) | F(VIRT_SSBD) | F(AMD_SSB_NO);

		F(AMD_IBPB) | F(AMD_IBRS) | F(AMD_SSBD) | F(VIRT_SSBD) |

		F(AMD_SSB_NO);



	/* cpuid 0xC0000001.edx */

	const u32 kvm_cpuid_C000_0001_edx_x86_features =
@@ -664,7 +665,12 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function, 
			entry->ebx |= F(VIRT_SSBD);

		entry->ebx &= kvm_cpuid_8000_0008_ebx_x86_features;

		cpuid_mask(&entry->ebx, CPUID_8000_0008_EBX);

		if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD))

		/*

		 * The preference is to use SPEC CTRL MSR instead of the

		 * VIRT_SPEC MSR.

		 */

		if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD) &&

		    !boot_cpu_has(X86_FEATURE_AMD_SSBD))

			entry->ebx |= F(VIRT_SSBD);

		break;

	}

arch/x86/kvm/svm.c

+5 −3
Original line number Diff line number Diff line
@@ -4115,7 +4115,8 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) 
		break;

	case MSR_IA32_SPEC_CTRL:

		if (!msr_info->host_initiated &&

		    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS))

		    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS) &&

		    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD))

			return 1;



		msr_info->data = svm->spec_ctrl;
@@ -4217,11 +4218,12 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) 
		break;

	case MSR_IA32_SPEC_CTRL:

		if (!msr->host_initiated &&

		    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS))

		    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS) &&

		    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD))

			return 1;



		/* The STIBP bit doesn't fault even if it's not advertised */

		if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP))

		if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP | SPEC_CTRL_SSBD))

			return 1;



		svm->spec_ctrl = data;