Subject: [PATCH 1/2] powerpc/perf: Fix kernel address leak to userspace via BHRB buffer

From: Madhavan Srinivasan <[email-masked]>
Date: Sun, 4 Mar 2018 17:25:17 +0530

The current Branch History Rolling Buffer (BHRB) code does
not check for any privilege levels before updating the data
from BHRB. This leaks kernel addresses to userspace even when
profiling only with userspace privileges. Add proper checks
to prevent it.

Signed-off-by: Madhavan Srinivasan <[email-masked]>
---
 arch/powerpc/perf/core-book3s.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index f89bbd54ecec..337db5831749 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -457,6 +457,10 @@ static void power_pmu_bhrb_read(struct cpu_hw_events *cpuhw)
 				/* invalid entry */
 				continue;
 
+			if (perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN) &&
+				is_kernel_addr(addr))
+				continue;
+
 			/* Branches are read most recent first (ie. mfbhrb 0 is
 			 * the most recent branch).
 			 * There are two types of valid entries:
-- 
2.7.4