cpu: Re-enable CPU mitigations by default for !X86 architectures

commit fe42754b94a42d08cf9501790afc25c4f6a5f631 upstream.

Rename x86's to CPU_MITIGATIONS, define it in generic code, and force it
on for all architectures exception x86.  A recent commit to turn
mitigations off by default if SPECULATION_MITIGATIONS=n kinda sorta
missed that "cpu_mitigations" is completely generic, whereas
SPECULATION_MITIGATIONS is x86-specific.

Rename x86's SPECULATIVE_MITIGATIONS instead of keeping both and have it
select CPU_MITIGATIONS, as having two configs for the same thing is
unnecessary and confusing.  This will also allow x86 to use the knob to
manage mitigations that aren't strictly related to speculative
execution.

Use another Kconfig to communicate to common code that CPU_MITIGATIONS
is already defined instead of having x86's menu depend on the common
CPU_MITIGATIONS.  This allows keeping a single point of contact for all
of x86's mitigations, and it's not clear that other architectures *want*
to allow disabling mitigations at compile-time.

Fixes: f337a6a21e2f ("x86/cpu: Actually turn off mitigations by default for SPECULATION_MITIGATIONS=n")
Closes: https://lkml.kernel.org/r/20240413115324.53303a68%40canb.auug.org.au
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20240420000556.2645001-2-seanjc@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/Kconfig b/arch/Kconfig
index 240277d5626c81463f4f1fe6a4b3f2a70ef2abfe..72e4cef062aca4f47cddf28e408b2665114c187f 100644 (file)
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -9,6 +9,14 @@
 #
 source "arch/$(SRCARCH)/Kconfig"
 
+config ARCH_CONFIGURES_CPU_MITIGATIONS
+       bool
+
+if !ARCH_CONFIGURES_CPU_MITIGATIONS
+config CPU_MITIGATIONS
+       def_bool y
+endif
+
 menu "General architecture-dependent options"
 
 config CRASH_CORE

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 9b3fa05e4622633be16a90f90f3814096e8f9f04..0c802ade8040670e7c2449f7f9340fda41dd8049 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -57,6 +57,7 @@ config X86
        select ACPI_LEGACY_TABLES_LOOKUP        if ACPI
        select ACPI_SYSTEM_POWER_STATES_SUPPORT if ACPI
        select ARCH_32BIT_OFF_T                 if X86_32
+       select ARCH_CONFIGURES_CPU_MITIGATIONS
        select ARCH_CLOCKSOURCE_INIT
        select ARCH_HAS_ACPI_TABLE_UPGRADE      if ACPI
        select ARCH_HAS_CPU_FINALIZE_INIT
@@ -2408,17 +2409,17 @@ config CC_HAS_SLS
 config CC_HAS_RETURN_THUNK
        def_bool $(cc-option,-mfunction-return=thunk-extern)
 
-menuconfig SPECULATION_MITIGATIONS
-       bool "Mitigations for speculative execution vulnerabilities"
+menuconfig CPU_MITIGATIONS
+       bool "Mitigations for CPU vulnerabilities"
        default y
        help
-         Say Y here to enable options which enable mitigations for
-         speculative execution hardware vulnerabilities.
+         Say Y here to enable options which enable mitigations for hardware
+         vulnerabilities (usually related to speculative execution).
 
          If you say N, all mitigations will be disabled. You really
          should know what you are doing to say so.
 
-if SPECULATION_MITIGATIONS
+if CPU_MITIGATIONS
 
 config PAGE_TABLE_ISOLATION
        bool "Remove the kernel mapping in user mode"

diff --git a/kernel/cpu.c b/kernel/cpu.c
index d025eb4f793209601e376ef018a064c1c3175cb3..d84ba5a13d1711ec5f4c97dd5ecb6d84aecf7668 100644 (file)
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -2600,8 +2600,8 @@ enum cpu_mitigations {
 };
 
 static enum cpu_mitigations cpu_mitigations __ro_after_init =
-       IS_ENABLED(CONFIG_SPECULATION_MITIGATIONS) ? CPU_MITIGATIONS_AUTO :
-                                                    CPU_MITIGATIONS_OFF;
+       IS_ENABLED(CONFIG_CPU_MITIGATIONS) ? CPU_MITIGATIONS_AUTO :
+                                            CPU_MITIGATIONS_OFF;
 
 static int __init mitigations_parse_cmdline(char *arg)
 {