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

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

diff --git a/arch/Kconfig b/arch/Kconfig
index 65afb1de48b36e843bd665a91df6b33badfd23d1..30f7930275d8388d6fca8ddcd97fbd56ec007873 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 ARCH_HAS_SUBPAGE_FAULTS

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 4474bf32d0a4970daec7fad3f12f8aa4a9e43871..619a04d5c1310ddd22b512f19ecec0b387242813 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -62,6 +62,7 @@ config X86
        select ACPI_HOTPLUG_CPU                 if ACPI_PROCESSOR && HOTPLUG_CPU
        select ARCH_32BIT_OFF_T                 if X86_32
        select ARCH_CLOCKSOURCE_INIT
+       select ARCH_CONFIGURES_CPU_MITIGATIONS
        select ARCH_CORRECT_STACKTRACE_ON_KRETPROBE
        select ARCH_ENABLE_HUGEPAGE_MIGRATION if X86_64 && HUGETLB_PAGE && MIGRATION
        select ARCH_ENABLE_MEMORY_HOTPLUG if X86_64
@@ -2488,17 +2489,17 @@ config PREFIX_SYMBOLS
        def_bool y
        depends on CALL_PADDING && !CFI_CLANG
 
-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 MITIGATION_PAGE_TABLE_ISOLATION
        bool "Remove the kernel mapping in user mode"

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 07ad53b7f11952080e890ed91f99f3e762bf984d..bb0ff275fb467d736cf798c24ab5b850001fefa1 100644 (file)
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -3207,8 +3207,8 @@ 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)
 {