Re: [PATCH v2] powerpc/64s: support nospectre_v2 cmdline option

[Andrew Donnellan]

On 7/5/19 12:43 pm, Christopher M. Riedl wrote:

Add support for disabling the kernel implemented spectre v2 mitigation
(count cache flush on context switch) via the nospectre_v2 cmdline
option.

Suggested-by: Michael Ellerman <m...@ellerman.id.au>
Signed-off-by: Christopher M. Riedl <c...@informatik.wtf>

Reviewed-by: Andrew Donnellan <a...@linux.ibm.com>

---
v1->v2:
        add call to toggle_count_cache_flush(false)

  arch/powerpc/kernel/security.c | 16 ++++++++++++++--
  1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/security.c b/arch/powerpc/kernel/security.c
index b33bafb8fcea..d775da9b9227 100644
--- a/arch/powerpc/kernel/security.c
+++ b/arch/powerpc/kernel/security.c
@@ -28,7 +28,7 @@ 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

@@ -106,7 +106,7 @@ 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;
@@ -114,6 +114,9 @@ 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)
@@ -391,6 +394,15 @@ static void toggle_count_cache_flush(bool enable)

void setup_count_cache_flush(void)

  {
+       if (no_spectrev2) {
+               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");
+
+               toggle_count_cache_flush(false);
+               return;
+       }
+
        toggle_count_cache_flush(true);
  }

--
Andrew Donnellan              OzLabs, ADL Canberra
a...@linux.ibm.com             IBM Australia Limited