Subject: [PATCH 2/2] powerpc/perf: Fix the kernel address leak to userspace via SDAR

From: Madhavan Srinivasan <[email-masked]>
Date: Sun, 4 Mar 2018 17:25:18 +0530

Sampled Data Address Register (SDAR) is a 64-bit
register that contains the effective address of
the storage operand of an instruction that was
being executed, possibly out-of-order, at or around
the time that the Performance Monitor alert occurred.

In certain scenario SDAR happen to contain the kernel
address even for userspace only sampling. Add checks
to prevent it.

Signed-off-by: Madhavan Srinivasan <[email-masked]>
---
 arch/powerpc/perf/core-book3s.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 337db5831749..c4525323d691 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -95,7 +95,7 @@ static inline unsigned long perf_ip_adjust(struct pt_regs *regs)
 {
 	return 0;
 }
-static inline void perf_get_data_addr(struct pt_regs *regs, u64 *addrp) { }
+static inline void perf_get_data_addr(struct pt_regs *regs, u64 *addrp, struct perf_event *event) { }
 static inline u32 perf_get_misc_flags(struct pt_regs *regs)
 {
 	return 0;
@@ -174,7 +174,7 @@ static inline unsigned long perf_ip_adjust(struct pt_regs *regs)
  * pointed to by SIAR; this is indicated by the [POWER6_]MMCRA_SDSYNC, the
  * [POWER7P_]MMCRA_SDAR_VALID bit in MMCRA, or the SDAR_VALID bit in SIER.
  */
-static inline void perf_get_data_addr(struct pt_regs *regs, u64 *addrp)
+static inline void perf_get_data_addr(struct pt_regs *regs, u64 *addrp, struct perf_event *event)
 {
 	unsigned long mmcra = regs->dsisr;
 	bool sdar_valid;
@@ -198,6 +198,11 @@ static inline void perf_get_data_addr(struct pt_regs *regs, u64 *addrp)
 
 	if (!(mmcra & MMCRA_SAMPLE_ENABLE) || sdar_valid)
 		*addrp = mfspr(SPRN_SDAR);
+
+	if (perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN) &&
+		(event->attr.exclude_kernel || event->attr.exclude_hv) &&
+		is_kernel_addr(mfspr(SPRN_SDAR)))
+		*addrp = 0;
 }
 
 static bool regs_sihv(struct pt_regs *regs)
@@ -2054,7 +2059,7 @@ static void record_and_restart(struct perf_event *event, unsigned long val,
 
 		if (event->attr.sample_type &
 		    (PERF_SAMPLE_ADDR | PERF_SAMPLE_PHYS_ADDR))
-			perf_get_data_addr(regs, &data.addr);
+			perf_get_data_addr(regs, &data.addr, event);
 
 		if (event->attr.sample_type & PERF_SAMPLE_BRANCH_STACK) {
 			struct cpu_hw_events *cpuhw;
-- 
2.7.4