powerpc/64s: support nospectre_v2 cmdline option

commit d8f0e0b073e1ec52a05f0c2a56318b47387d2f10 upstream.

Add support for disabling the kernel implemented spectre v2 mitigation
(count cache flush on context switch) via the nospectre_v2 and
mitigations=off cmdline options.

Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Christopher M. Riedl <cmr@informatik.wtf>
Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190524024647.381-1-cmr@informatik.wtf
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/powerpc/kernel/security.c b/arch/powerpc/kernel/security.c
index fe30ddfd51eead7b8669a80d38beff53d11527ff..32b3a44ee723149304964340e05ed4cbcb5ef8f8 100644 (file)
--- a/arch/powerpc/kernel/security.c
+++ b/arch/powerpc/kernel/security.c
@@ -29,7 +29,7 @@ static enum count_cache_flush_type count_cache_flush_type = COUNT_CACHE_FLUSH_NO
 bool barrier_nospec_enabled;
 static bool no_nospec;
 static bool btb_flush_enabled;
-#ifdef CONFIG_PPC_FSL_BOOK3E
+#if defined(CONFIG_PPC_FSL_BOOK3E) || defined(CONFIG_PPC_BOOK3S_64)
 static bool no_spectrev2;
 #endif
 
@@ -107,7 +107,7 @@ static __init int barrier_nospec_debugfs_init(void)
 device_initcall(barrier_nospec_debugfs_init);
 #endif /* CONFIG_DEBUG_FS */
 
-#ifdef CONFIG_PPC_FSL_BOOK3E
+#if defined(CONFIG_PPC_FSL_BOOK3E) || defined(CONFIG_PPC_BOOK3S_64)
 static int __init handle_nospectre_v2(char *p)
 {
        no_spectrev2 = true;
@@ -115,6 +115,9 @@ static int __init handle_nospectre_v2(char *p)
        return 0;
 }
 early_param("nospectre_v2", handle_nospectre_v2);
+#endif /* CONFIG_PPC_FSL_BOOK3E || CONFIG_PPC_BOOK3S_64 */
+
+#ifdef CONFIG_PPC_FSL_BOOK3E
 void setup_spectre_v2(void)
 {
        if (no_spectrev2)
@@ -390,7 +393,17 @@ static void toggle_count_cache_flush(bool enable)
 
 void setup_count_cache_flush(void)
 {
-       toggle_count_cache_flush(true);
+       bool enable = true;
+
+       if (no_spectrev2 || cpu_mitigations_off()) {
+               if (security_ftr_enabled(SEC_FTR_BCCTRL_SERIALISED) ||
+                   security_ftr_enabled(SEC_FTR_COUNT_CACHE_DISABLED))
+                       pr_warn("Spectre v2 mitigations not under software control, can't disable\n");
+
+               enable = false;
+       }
+
+       toggle_count_cache_flush(enable);
 }
 
 #ifdef CONFIG_DEBUG_FS