[SRU OEM-5.14 08/11] x86/speculation/srbds: Update SRBDS mitigation selection

[Thadeu Lima de Souza Cascardo]

From: Pawan Gupta <pawan.kumar.gupta at linux.intel.com>

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: Pawan Gupta <pawan.kumar.gupta at linux.intel.com>
Signed-off-by: Borislav Petkov <bp at suse.de>
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
CVE-2022-21166
CVE-2022-21123
CVE-2022-21125
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
---
 arch/x86/kernel/cpu/bugs.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 6108e5a294ea..3c3e4a466136 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -586,11 +586,13 @@ 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;
-- 
2.34.1