Commit e3a88d4c authored by David Kaplan's avatar David Kaplan Committed by Borislav Petkov (AMD)
Browse files

x86/bugs: Add attack vector controls for MDS 



Use attack vector controls to determine if MDS mitigation is required.
The global mitigations=off command now simply disables all attack vectors
so explicit checking of mitigations=off is no longer needed.

If cross-thread attack mitigations are required, disable SMT.

Signed-off-by: default avatarDavid Kaplan <david.kaplan@amd.com>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/20250707183316.1349127-6-david.kaplan@amd.com
parent 2d31d287

arch/x86/kernel/cpu/bugs.c

+9 −5
Original line number Diff line number Diff line
@@ -441,13 +441,17 @@ static bool verw_clear_cpu_buf_mitigation_selected __ro_after_init; 


static void __init mds_select_mitigation(void)

{

	if (!boot_cpu_has_bug(X86_BUG_MDS) || cpu_mitigations_off()) {

	if (!boot_cpu_has_bug(X86_BUG_MDS)) {

		mds_mitigation = MDS_MITIGATION_OFF;

		return;

	}



	if (mds_mitigation == MDS_MITIGATION_AUTO)

	if (mds_mitigation == MDS_MITIGATION_AUTO) {

		if (should_mitigate_vuln(X86_BUG_MDS))

			mds_mitigation = MDS_MITIGATION_FULL;

		else

			mds_mitigation = MDS_MITIGATION_OFF;

	}



	if (mds_mitigation == MDS_MITIGATION_OFF)

		return;
@@ -457,7 +461,7 @@ static void __init mds_select_mitigation(void) 


static void __init mds_update_mitigation(void)

{

	if (!boot_cpu_has_bug(X86_BUG_MDS) || cpu_mitigations_off())

	if (!boot_cpu_has_bug(X86_BUG_MDS))

		return;



	/* If TAA, MMIO, or RFDS are being mitigated, MDS gets mitigated too. */
@@ -478,7 +482,7 @@ static void __init mds_apply_mitigation(void) 
	    mds_mitigation == MDS_MITIGATION_VMWERV) {

		setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);

		if (!boot_cpu_has(X86_BUG_MSBDS_ONLY) &&

		    (mds_nosmt || cpu_mitigations_auto_nosmt()))

		    (mds_nosmt || smt_mitigations == SMT_MITIGATIONS_ON))

			cpu_smt_disable(false);

	}

}