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

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Mon, Jul 04, 2022 at 03:53:25PM +0100, Andrew Kilroy escreveu:
> 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.

I'm not seeing this kernel patch applied to tip/master or
torvalds/master, what is the status of that part? Then I can look at the
tooling part.

- Arnaldo
 
> Signed-off-by: Andrew Kilroy <andrew.kilroy@arm.com>
> ---
>  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

-- 

- Arnaldo