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Commit bc64f38b authored by Pawan Gupta's avatar Pawan Gupta Committed by Greg Kroah-Hartman
Browse files

x86/speculation/srbds: Update SRBDS mitigation selection 



commit 22cac9c677c95f3ac5c9244f8ca0afdc7c8afb19 upstream

Currently, Linux disables SRBDS mitigation on CPUs not affected by
MDS and have the TSX feature disabled. On such CPUs, secrets cannot
be extracted from CPU fill buffers using MDS or TAA. Without SRBDS
mitigation, Processor MMIO Stale Data vulnerabilities can be used to
extract RDRAND, RDSEED, and EGETKEY data.

Do not disable SRBDS mitigation by default when CPU is also affected by
Processor MMIO Stale Data vulnerabilities.

Signed-off-by: default avatarPawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 020ce749

arch/x86/kernel/cpu/bugs.c

+5 −3
Original line number Diff line number Diff line
@@ -578,11 +578,13 @@ static void __init srbds_select_mitigation(void) 
		return;



	/*

	 * Check to see if this is one of the MDS_NO systems supporting

	 * TSX that are only exposed to SRBDS when TSX is enabled.

	 * Check to see if this is one of the MDS_NO systems supporting TSX that

	 * are only exposed to SRBDS when TSX is enabled or when CPU is affected

	 * by Processor MMIO Stale Data vulnerability.

	 */

	ia32_cap = x86_read_arch_cap_msr();

	if ((ia32_cap & ARCH_CAP_MDS_NO) && !boot_cpu_has(X86_FEATURE_RTM))

	if ((ia32_cap & ARCH_CAP_MDS_NO) && !boot_cpu_has(X86_FEATURE_RTM) &&

	    !boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA))

		srbds_mitigation = SRBDS_MITIGATION_TSX_OFF;

	else if (boot_cpu_has(X86_FEATURE_HYPERVISOR))

		srbds_mitigation = SRBDS_MITIGATION_HYPERVISOR;