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x86/bugs: Add attack vector controls for MDS

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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: David Kaplan <david.kaplan@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/20250707183316.1349127-6-david.kaplan@amd.com
This commit is contained in:
David Kaplan
2025-07-07 13:33:00 -05:00
committed by Borislav Petkov (AMD)
parent 2d31d28746
commit e3a88d4c06
1 changed files with 9 additions and 5 deletions
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14
arch/x86/kernel/cpu/bugs.c
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@@ -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)
mds_mitigation = MDS_MITIGATION_FULL;
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);
}
}