[PATCH] powerpc/security: Fix spectre_v2 reporting

Michael Ellerman mpe at ellerman.id.au
Thu Mar 21 15:24:33 AEDT 2019

When I updated the spectre_v2 reporting to handle software count cache
flush I got the logic wrong when there's no software count cache
enabled at all.

The result is that on systems with the software count cache flush
disabled we print:

  Mitigation: Indirect branch cache disabled, Software count cache flush

Which correctly indicates that the count cache is disabled, but
incorrectly says the software count cache flush is enabled.

The root of the problem is that we are trying to handle all
combinations of options. But we know now that we only expect to see
the software count cache flush enabled if the other options are false.

So split the two cases, which simplifies the logic and fixes the bug.
We were also missing a space before "(hardware accelerated)".

The result is we see one of:

  Mitigation: Indirect branch serialisation (kernel only)
  Mitigation: Indirect branch cache disabled
  Mitigation: Software count cache flush
  Mitigation: Software count cache flush (hardware accelerated)

Fixes: ee13cb249fab ("powerpc/64s: Add support for software count cache flush")
Cc: stable at vger.kernel.org # v4.19+
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
 arch/powerpc/kernel/security.c | 23 ++++++++---------------
 1 file changed, 8 insertions(+), 15 deletions(-)

diff --git a/arch/powerpc/kernel/security.c b/arch/powerpc/kernel/security.c
index 9b8631533e02..b33bafb8fcea 100644
--- a/arch/powerpc/kernel/security.c
+++ b/arch/powerpc/kernel/security.c
@@ -190,29 +190,22 @@ ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr, c
 	bcs = security_ftr_enabled(SEC_FTR_BCCTRL_SERIALISED);
 	ccd = security_ftr_enabled(SEC_FTR_COUNT_CACHE_DISABLED);
-	if (bcs || ccd || count_cache_flush_type != COUNT_CACHE_FLUSH_NONE) {
-		bool comma = false;
+	if (bcs || ccd) {
 		seq_buf_printf(&s, "Mitigation: ");
-		if (bcs) {
+		if (bcs)
 			seq_buf_printf(&s, "Indirect branch serialisation (kernel only)");
-			comma = true;
-		}
-		if (ccd) {
-			if (comma)
-				seq_buf_printf(&s, ", ");
-			seq_buf_printf(&s, "Indirect branch cache disabled");
-			comma = true;
-		}
-		if (comma)
+		if (bcs && ccd)
 			seq_buf_printf(&s, ", ");
-		seq_buf_printf(&s, "Software count cache flush");
+		if (ccd)
+			seq_buf_printf(&s, "Indirect branch cache disabled");
+	} else if (count_cache_flush_type != COUNT_CACHE_FLUSH_NONE) {
+		seq_buf_printf(&s, "Mitigation: Software count cache flush");
 		if (count_cache_flush_type == COUNT_CACHE_FLUSH_HW)
-			seq_buf_printf(&s, "(hardware accelerated)");
+			seq_buf_printf(&s, " (hardware accelerated)");
 	} else if (btb_flush_enabled) {
 		seq_buf_printf(&s, "Mitigation: Branch predictor state flush");
 	} else {

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