x86/bugs: Remove GDS Force Kconfig option

Remove the MITIGATION_GDS_FORCE Kconfig option, which aggressively disables
AVX as a mitigation for Gather Data Sampling (GDS) vulnerabilities. This
option is not widely used by distros.

While removing the Kconfig option, retain the runtime configuration ability
through the `gather_data_sampling=force` kernel parameter. This allows users
to still enable this aggressive mitigation if needed, without baking it into
the kernel configuration.

Simplify the kernel configuration while maintaining flexibility for runtime
mitigation choices.

Suggested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Daniel Sneddon <daniel.sneddon@linux.intel.com>
Link: https://lore.kernel.org/r/20240729164105.554296-11-leitao@debian.org

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 2e72a07981b2509f471779c2d1103cdbe34444a9..ab5b210c8315b75cde615a3e328919b291e1f5ef 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2610,25 +2610,6 @@ config MITIGATION_SLS
          against straight line speculation. The kernel image might be slightly
          larger.
 
-config MITIGATION_GDS_FORCE
-       bool "Force GDS Mitigation"
-       depends on CPU_SUP_INTEL
-       default n
-       help
-         Gather Data Sampling (GDS) is a hardware vulnerability which allows
-         unprivileged speculative access to data which was previously stored in
-         vector registers.
-
-         This option is equivalent to setting gather_data_sampling=force on the
-         command line. The microcode mitigation is used if present, otherwise
-         AVX is disabled as a mitigation. On affected systems that are missing
-         the microcode any userspace code that unconditionally uses AVX will
-         break with this option set.
-
-         Setting this option on systems not vulnerable to GDS has no effect.
-
-         If in doubt, say N.
-
 config MITIGATION_RFDS
        bool "RFDS Mitigation"
        depends on CPU_SUP_INTEL

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index a7f20ae2fcf4f47801b2c73c1dbc4b6d8c00fdbe..b2e752eeb098e5f78a9bfffff49ac35f64eb50d4 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -735,11 +735,7 @@ enum gds_mitigations {
        GDS_MITIGATION_HYPERVISOR,
 };
 
-#if IS_ENABLED(CONFIG_MITIGATION_GDS_FORCE)
-static enum gds_mitigations gds_mitigation __ro_after_init = GDS_MITIGATION_FORCE;
-#else
 static enum gds_mitigations gds_mitigation __ro_after_init = GDS_MITIGATION_FULL;
-#endif
 
 static const char * const gds_strings[] = {
        [GDS_MITIGATION_OFF]            = "Vulnerable",