[PATCH 1/8] perf arm64: Send pointer auth masks to ring buffer

[Andrew Kilroy]

Perf report cannot produce callgraphs using dwarf on arm64 where pointer
authentication is enabled.  This is because libunwind and libdw cannot
unmangle instruction pointers that have a pointer authentication code
(PAC) embedded in them.

libunwind and libdw need to be given an instruction mask which they can
use to arrive at the correct return address that does not contain the
PAC.

The bits in the return address that contain the PAC can differ by
process, so this patch adds a new sample field PERF_SAMPLE_ARCH_1
to allow the kernel to send the masks up to userspace perf.

This field can be used in a architecture specific fashion, but on
aarch64, it contains the ptrauth mask information.

Signed-off-by: Andrew Kilroy <andrew.kilroy@xxxxxxx>
---
 arch/arm64/include/asm/arch_sample_data.h | 38 +++++++++++++++++++++++
 arch/arm64/kernel/Makefile                |  2 +-
 arch/arm64/kernel/arch_sample_data.c      | 37 ++++++++++++++++++++++
 include/linux/perf_event.h                | 24 ++++++++++++++
 include/uapi/linux/perf_event.h           |  5 ++-
 kernel/events/core.c                      | 35 +++++++++++++++++++++
 6 files changed, 139 insertions(+), 2 deletions(-)
 create mode 100644 arch/arm64/include/asm/arch_sample_data.h
 create mode 100644 arch/arm64/kernel/arch_sample_data.c

diff --git a/arch/arm64/include/asm/arch_sample_data.h b/arch/arm64/include/asm/arch_sample_data.h
new file mode 100644
index 000000000000..83fda293b1fc
--- /dev/null
+++ b/arch/arm64/include/asm/arch_sample_data.h
@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _ASM_ARCH_SAMPLE_DATA_H
+#define _ASM_ARCH_SAMPLE_DATA_H
+
+#include <linux/types.h>
+
+/*
+ * Structure holding masks to help userspace stack unwinding
+ * in the presence of arm64 pointer authentication.
+ */
+struct ptrauth_info {
+	/*
+	 * Bits 0, 1, 2, 3, 4 may be set to on, to indicate which keys are being used
+	 * The APIAKEY, APIBKEY, APDAKEY, APDBKEY, or the APGAKEY respectively.
+	 * Where all bits are off, pointer authentication is not in use for the
+	 * process.
+	 */
+	u64 enabled_keys;
+
+	/*
+	 * The on bits represent which bits in an instruction pointer
+	 * constitute the pointer authentication code.
+	 */
+	u64 insn_mask;
+
+	/*
+	 * The on bits represent which bits in a data pointer constitute the
+	 * pointer authentication code.
+	 */
+	u64 data_mask;
+};
+
+struct arch_sample_data {
+	struct ptrauth_info ptrauth;
+};
+
+#endif
diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index fa7981d0d917..843c6e0e2393 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -44,7 +44,7 @@ obj-$(CONFIG_KUSER_HELPERS)		+= kuser32.o
 obj-$(CONFIG_FUNCTION_TRACER)		+= ftrace.o entry-ftrace.o
 obj-$(CONFIG_MODULES)			+= module.o
 obj-$(CONFIG_ARM64_MODULE_PLTS)		+= module-plts.o
-obj-$(CONFIG_PERF_EVENTS)		+= perf_regs.o perf_callchain.o
+obj-$(CONFIG_PERF_EVENTS)		+= perf_regs.o perf_callchain.o arch_sample_data.o
 obj-$(CONFIG_HW_PERF_EVENTS)		+= perf_event.o
 obj-$(CONFIG_HAVE_HW_BREAKPOINT)	+= hw_breakpoint.o
 obj-$(CONFIG_CPU_PM)			+= sleep.o suspend.o
diff --git a/arch/arm64/kernel/arch_sample_data.c b/arch/arm64/kernel/arch_sample_data.c
new file mode 100644
index 000000000000..2d47e8db0dbe
--- /dev/null
+++ b/arch/arm64/kernel/arch_sample_data.c
@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <asm/arch_sample_data.h>
+#include <linux/perf_event.h>
+
+inline void perf_output_sample_arch_1(struct perf_output_handle *handle,
+				      struct perf_event_header *header,
+				      struct perf_sample_data *data,
+				      struct perf_event *event)
+{
+	perf_output_put(handle, data->arch.ptrauth.enabled_keys);
+	perf_output_put(handle, data->arch.ptrauth.insn_mask);
+	perf_output_put(handle, data->arch.ptrauth.data_mask);
+}
+
+inline void perf_prepare_sample_arch_1(struct perf_event_header *header,
+				       struct perf_sample_data *data,
+				       struct perf_event *event,
+				       struct pt_regs *regs)
+{
+	struct task_struct *task = current;
+	int keys_result = ptrauth_get_enabled_keys(task);
+	u64 user_pac_mask = keys_result > 0 ? ptrauth_user_pac_mask() : 0;
+
+	data->arch.ptrauth.enabled_keys = keys_result > 0 ? keys_result : 0;
+	data->arch.ptrauth.insn_mask = user_pac_mask;
+	data->arch.ptrauth.data_mask = user_pac_mask;
+
+	header->size += (3 * sizeof(u64));
+}
+
+inline int perf_event_open_request_arch_1(void)
+{
+	return 0;
+}
+
+
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index da759560eec5..8a99942989ce 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -999,6 +999,29 @@ int perf_event_read_local(struct perf_event *event, u64 *value,
 extern u64 perf_event_read_value(struct perf_event *event,
 				 u64 *enabled, u64 *running);
 
+void perf_output_sample_arch_1(struct perf_output_handle *handle,
+			       struct perf_event_header *header,
+			       struct perf_sample_data *data,
+			       struct perf_event *event);
+
+void perf_prepare_sample_arch_1(struct perf_event_header *header,
+				struct perf_sample_data *data,
+				struct perf_event *event,
+				struct pt_regs *regs);
+
+int perf_event_open_request_arch_1(void);
+
+#if IS_ENABLED(CONFIG_ARM64)
+
+#define HAS_ARCH_SAMPLE_DATA
+#include <asm/arch_sample_data.h>
+
+#endif
+
+#ifndef HAS_ARCH_SAMPLE_DATA
+struct arch_sample_data {
+};
+#endif
 
 struct perf_sample_data {
 	/*
@@ -1041,6 +1064,7 @@ struct perf_sample_data {
 	u64				cgroup;
 	u64				data_page_size;
 	u64				code_page_size;
+	struct arch_sample_data		arch;
 } ____cacheline_aligned;
 
 /* default value for data source */
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index d37629dbad72..821bf5ff6a19 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -162,12 +162,15 @@ enum perf_event_sample_format {
 	PERF_SAMPLE_DATA_PAGE_SIZE		= 1U << 22,
 	PERF_SAMPLE_CODE_PAGE_SIZE		= 1U << 23,
 	PERF_SAMPLE_WEIGHT_STRUCT		= 1U << 24,
+	PERF_SAMPLE_ARCH_1			= 1U << 25,
 
-	PERF_SAMPLE_MAX = 1U << 25,		/* non-ABI */
+	PERF_SAMPLE_MAX = 1U << 26,		/* non-ABI */
 
 	__PERF_SAMPLE_CALLCHAIN_EARLY		= 1ULL << 63, /* non-ABI; internal use */
 };
 
+#define PERF_SAMPLE_ARM64_PTRAUTH PERF_SAMPLE_ARCH_1
+
 #define PERF_SAMPLE_WEIGHT_TYPE	(PERF_SAMPLE_WEIGHT | PERF_SAMPLE_WEIGHT_STRUCT)
 /*
  * values to program into branch_sample_type when PERF_SAMPLE_BRANCH is set
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 80782cddb1da..89ab8120f4f0 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6957,6 +6957,29 @@ static inline bool perf_sample_save_hw_index(struct perf_event *event)
 	return event->attr.branch_sample_type & PERF_SAMPLE_BRANCH_HW_INDEX;
 }
 
+#ifndef HAS_ARCH_SAMPLE_DATA
+
+inline void perf_output_sample_arch_1(struct perf_output_handle *handle __maybe_unused,
+				      struct perf_event_header *header __maybe_unused,
+				      struct perf_sample_data *data __maybe_unused,
+				      struct perf_event *event __maybe_unused)
+{
+}
+
+inline void perf_prepare_sample_arch_1(struct perf_event_header *header __maybe_unused,
+				       struct perf_sample_data *data __maybe_unused,
+				       struct perf_event *event __maybe_unused,
+				       struct pt_regs *regs __maybe_unused)
+{
+}
+
+inline int perf_event_open_request_arch_1(void)
+{
+	return -EINVAL;
+}
+
+#endif
+
 void perf_output_sample(struct perf_output_handle *handle,
 			struct perf_event_header *header,
 			struct perf_sample_data *data,
@@ -7125,6 +7148,9 @@ void perf_output_sample(struct perf_output_handle *handle,
 			perf_aux_sample_output(event, handle, data);
 	}
 
+	if (sample_type & PERF_SAMPLE_ARCH_1)
+		perf_output_sample_arch_1(handle, header, data, event);
+
 	if (!event->attr.watermark) {
 		int wakeup_events = event->attr.wakeup_events;
 
@@ -7427,6 +7453,9 @@ void perf_prepare_sample(struct perf_event_header *header,
 	if (sample_type & PERF_SAMPLE_CODE_PAGE_SIZE)
 		data->code_page_size = perf_get_page_size(data->ip);
 
+	if (sample_type & PERF_SAMPLE_ARCH_1)
+		perf_prepare_sample_arch_1(header, data, event, regs);
+
 	if (sample_type & PERF_SAMPLE_AUX) {
 		u64 size;
 
@@ -12074,6 +12103,12 @@ SYSCALL_DEFINE5(perf_event_open,
 			return err;
 	}
 
+	if (attr.sample_type & PERF_SAMPLE_ARCH_1) {
+		err = perf_event_open_request_arch_1();
+		if (err)
+			return err;
+	}
+
 	/*
 	 * In cgroup mode, the pid argument is used to pass the fd
 	 * opened to the cgroup directory in cgroupfs. The cpu argument
-- 
2.17.1