The following commit has been merged into the x86/bugs branch of tip:
Commit-ID: 2d31d2874663cde2cab8c18bfb52ed8be6dfa958
Gitweb: https://git.kernel.org/tip/2d31d2874663cde2cab8c18bfb52ed8be6dfa958
Author: David Kaplan <david.kaplan@amd.com>
AuthorDate: Mon, 07 Jul 2025 13:32:59 -05:00
Committer: Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Fri, 11 Jul 2025 17:56:40 +02:00
x86/bugs: Define attack vectors relevant for each bug
Add a function which defines which vulnerabilities should be mitigated
based on the selected attack vector controls. The selections here are
based on the individual characteristics of each vulnerability.
Signed-off-by: David Kaplan <david.kaplan@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/20250707183316.1349127-5-david.kaplan@amd.com
---
arch/x86/kernel/cpu/bugs.c | 56 +++++++++++++++++++++++++++++++++++++-
1 file changed, 56 insertions(+)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 88769c4..b083e7e 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -332,6 +332,62 @@ static void x86_amd_ssb_disable(void)
#undef pr_fmt
#define pr_fmt(fmt) "MDS: " fmt
+/*
+ * Returns true if vulnerability should be mitigated based on the
+ * selected attack vector controls.
+ *
+ * See Documentation/admin-guide/hw-vuln/attack_vector_controls.rst
+ */
+static bool __init should_mitigate_vuln(unsigned int bug)
+{
+ switch (bug) {
+ /*
+ * The only runtime-selected spectre_v1 mitigations in the kernel are
+ * related to SWAPGS protection on kernel entry. Therefore, protection
+ * is only required for the user->kernel attack vector.
+ */
+ case X86_BUG_SPECTRE_V1:
+ return cpu_attack_vector_mitigated(CPU_MITIGATE_USER_KERNEL);
+
+ case X86_BUG_SPECTRE_V2:
+ case X86_BUG_RETBLEED:
+ case X86_BUG_SRSO:
+ case X86_BUG_L1TF:
+ case X86_BUG_ITS:
+ return cpu_attack_vector_mitigated(CPU_MITIGATE_USER_KERNEL) ||
+ cpu_attack_vector_mitigated(CPU_MITIGATE_GUEST_HOST);
+
+ case X86_BUG_SPECTRE_V2_USER:
+ return cpu_attack_vector_mitigated(CPU_MITIGATE_USER_USER) ||
+ cpu_attack_vector_mitigated(CPU_MITIGATE_GUEST_GUEST);
+
+ /*
+ * All the vulnerabilities below allow potentially leaking data
+ * across address spaces. Therefore, mitigation is required for
+ * any of these 4 attack vectors.
+ */
+ case X86_BUG_MDS:
+ case X86_BUG_TAA:
+ case X86_BUG_MMIO_STALE_DATA:
+ case X86_BUG_RFDS:
+ case X86_BUG_SRBDS:
+ return cpu_attack_vector_mitigated(CPU_MITIGATE_USER_KERNEL) ||
+ cpu_attack_vector_mitigated(CPU_MITIGATE_GUEST_HOST) ||
+ cpu_attack_vector_mitigated(CPU_MITIGATE_USER_USER) ||
+ cpu_attack_vector_mitigated(CPU_MITIGATE_GUEST_GUEST);
+
+ case X86_BUG_GDS:
+ return cpu_attack_vector_mitigated(CPU_MITIGATE_USER_KERNEL) ||
+ cpu_attack_vector_mitigated(CPU_MITIGATE_GUEST_HOST) ||
+ cpu_attack_vector_mitigated(CPU_MITIGATE_USER_USER) ||
+ cpu_attack_vector_mitigated(CPU_MITIGATE_GUEST_GUEST) ||
+ (smt_mitigations != SMT_MITIGATIONS_OFF);
+ default:
+ WARN(1, "Unknown bug %x\n", bug);
+ return false;
+ }
+}
+
/* Default mitigation for MDS-affected CPUs */
static enum mds_mitigations mds_mitigation __ro_after_init =
IS_ENABLED(CONFIG_MITIGATION_MDS) ? MDS_MITIGATION_AUTO : MDS_MITIGATION_OFF;