[lttng-dev] [PATCH lttng-modules v6 3/5] Extract the FDs and flags from poll and ppoll

Mathieu Desnoyers mathieu.desnoyers at efficios.com
Sat Apr 30 14:14:27 UTC 2016


----- On Apr 29, 2016, at 6:53 PM, Julien Desfossez jdesfossez at efficios.com wrote:

> Instead of printing the pointer address of the poll set, extract all the
> FDs and flags from the poll set. For now, we only output the
> standardized set of events to limit the verbosity of the output, we also
> extract the raw value. When we switch to CTF2 we will be able to hide
> unset fields and then we will extract all the fields.
> 
> Here is an example of output with one FD:
> syscall_entry_poll: {
>  timeout_msecs = -1, nfds = 1, fds_length = 1,
>  fds = [
>    [0] = { fd = 4, raw_events = 0x5, events = { POLLIN = 1, POLLPRI = 0,
>            POLLOUT = 1, POLLERR = 0, POLLHUP = 0, padding = 0 } } ]
> }
> 
> syscall_exit_poll: {
>  ret = 1, nfds = 1, fds_length = 1,
>  fds = [ [0] = { fd = 4, raw_events = 0x4, events = { POLLIN = 0,
>  POLLPRI = 0, POLLOUT = 1, POLLERR = 0, POLLHUP = 0, padding = 0 } } ] }
> 
> Signed-off-by: Julien Desfossez <jdesfossez at efficios.com>
> ---
> .../syscalls/headers/syscalls_pointers_override.h  | 254 +++++++++++++++++++++
> 1 file changed, 254 insertions(+)
> 
> diff --git a/instrumentation/syscalls/headers/syscalls_pointers_override.h
> b/instrumentation/syscalls/headers/syscalls_pointers_override.h
> index b9dd54a..11d5f3d 100644
> --- a/instrumentation/syscalls/headers/syscalls_pointers_override.h
> +++ b/instrumentation/syscalls/headers/syscalls_pointers_override.h
> @@ -301,4 +301,258 @@ SC_LTTNG_TRACEPOINT_EVENT_CODE(pselect6,
> )
> #endif /* defined(CONFIG_X86_32) || defined(CONFIG_X86_64) ||
> defined(CONFIG_ARM64) || defined(CONFIG_ARM) */
> 
> +#ifndef ONCE_LTTNG_TRACE_POLL_H
> +#define ONCE_LTTNG_TRACE_POLL_H
> +
> +#define LTTNG_POLL_NRFLAGS (POLLNVAL + 1)
> +#define POLL_FLAGS_PADDING_SIZE (sizeof(uint8_t) * BITS_PER_BYTE) - \
> +	ilog2(LTTNG_POLL_NRFLAGS - 1)
> +
> +/*
> + * Only extract the values specified by iBCS2 for now.
> + */
> +static struct lttng_event_field lttng_pollfd_flag_fields[] = {
> +	[ilog2(POLLIN)] = {
> +		.name = "POLLIN",
> +		.type = __type_integer(int, 1, 1, 0, __LITTLE_ENDIAN, 10, none),
> +	},
> +	[ilog2(POLLPRI)] = {
> +		.name = "POLLPRI",
> +		.type = __type_integer(int, 1, 1, 0, __LITTLE_ENDIAN, 10, none),
> +	},
> +	[ilog2(POLLOUT)] = {
> +		.name = "POLLOUT",
> +		.type = __type_integer(int, 1, 1, 0, __LITTLE_ENDIAN, 10, none),
> +	},
> +	[ilog2(POLLERR)] = {
> +		.name = "POLLERR",
> +		.type = __type_integer(int, 1, 1, 0, __LITTLE_ENDIAN, 10, none),
> +	},
> +	[ilog2(POLLHUP)] = {
> +		.name = "POLLHUP",
> +		.type = __type_integer(int, 1, 1, 0, __LITTLE_ENDIAN, 10, none),
> +	},
> +	[ilog2(POLLNVAL)] = {
> +		.name = "POLLNVAL",
> +		.type = __type_integer(int, 1, 1, 0, __LITTLE_ENDIAN, 10, none),
> +	},
> +	[ilog2(LTTNG_POLL_NRFLAGS)] = {
> +		.name = "padding",
> +		.type = __type_integer(int, POLL_FLAGS_PADDING_SIZE, 1, 0,
> +				__LITTLE_ENDIAN, 10, none),
> +	},
> +};
> +
> +static struct lttng_event_field lttng_pollfd_fields[] = {
> +	[0] = {
> +		.name = "fd",
> +		.type = __type_integer(int, 0, 0, 0, __BYTE_ORDER, 10, none),
> +	},
> +	[1] = {
> +		.name = "raw_events",
> +		.type = __type_integer(short, 0, 0, 0, __BYTE_ORDER, 16, none),
> +	},
> +	[2] = {
> +		.name = "events",
> +		.type = {
> +			.atype = atype_struct,
> +			.u._struct.nr_fields = ARRAY_SIZE(lttng_pollfd_flag_fields),
> +			.u._struct.fields = lttng_pollfd_flag_fields,
> +		}
> +	},
> +};
> +
> +static struct lttng_type lttng_pollfd_elem = {
> +	.atype = atype_struct,
> +	.u._struct.nr_fields = ARRAY_SIZE(lttng_pollfd_fields),
> +	.u._struct.fields = lttng_pollfd_fields,
> +};
> +#endif /* ONCE_LTTNG_TRACE_POLL_H */
> +
> +#define LTTNG_SYSCALL_POLL_locvar				\
> +	unsigned int fds_length, fds_max_len, alloc_fds;	\
> +	struct pollfd *fds;					\
> +	uint8_t overflow;
> +
> +#define LTTNG_SYSCALL_POLL_code_pre				\
> +	BUILD_BUG_ON(((ARRAY_SIZE(lttng_pollfd_flag_fields) - 1) +			\
> +			POLL_FLAGS_PADDING_SIZE) !=					\
> +				sizeof(uint8_t) * BITS_PER_BYTE);			\
> +	tp_locvar->fds = NULL;								\
> +	tp_locvar->overflow = 0;							\
> +											\
> +	sc_in(										\
> +		if (nfds * sizeof(struct pollfd) > PAGE_SIZE) {				\

This check is incorrect if nfds * sizeof(struct pollfd) overflows an
unsigned int. Should instead be:

if (nfds > PAGE_SIZE / sizeof(struct pollfd))

Please audit all other checks on input size for this kind of mistake.

> +			tp_locvar->fds_length = PAGE_SIZE / sizeof(struct pollfd);	\
> +			tp_locvar->fds_max_len = PAGE_SIZE / sizeof(struct pollfd);	\
> +			tp_locvar->overflow = 1;					\
> +		} else {								\
> +			tp_locvar->fds_length = nfds;					\
> +			tp_locvar->fds_max_len = nfds;					\
> +		}									\
> +		tp_locvar->alloc_fds = tp_locvar->fds_length * sizeof(struct pollfd);	\
> +	)										\
> +	/*										\
> +	 * On exit, the number of active FDs is determined by ret,			\
> +	 * nfds stays the same as the entry, but we only want to			\
> +	 * output the FDs that are relevant.						\
> +	 */										\
> +	sc_out(										\
> +		if (ret <= 0 || ret > nfds)						\
> +			goto error;							\
> +											\
> +		if (nfds * sizeof(struct pollfd) > PAGE_SIZE) {				\

same here.

Thanks,

Mathieu

> +			tp_locvar->fds_length = PAGE_SIZE / sizeof(struct pollfd);	\
> +			tp_locvar->fds_max_len = PAGE_SIZE / sizeof(struct pollfd);	\
> +			tp_locvar->overflow = 1;					\
> +		} else {								\
> +			tp_locvar->fds_length = ret;					\
> +			tp_locvar->fds_max_len = nfds;					\
> +		}									\
> +		tp_locvar->alloc_fds = tp_locvar->fds_max_len * sizeof(struct pollfd);	\
> +	)										\
> +	{										\
> +		int err;								\
> +											\
> +		tp_locvar->fds = kmalloc(tp_locvar->alloc_fds,				\
> +				GFP_ATOMIC | GFP_NOWAIT);				\
> +		if (!tp_locvar->fds)							\
> +			goto error;							\
> +		err = lib_ring_buffer_copy_from_user_check_nofault(			\
> +			tp_locvar->fds, ufds,						\
> +			nfds * sizeof(struct pollfd));					\
> +		if (err != 0)								\
> +			goto error;							\
> +	}										\
> +	goto end;									\
> +											\
> +error:											\
> +	tp_locvar->fds_length = 0;							\
> +	tp_locvar->fds_max_len = 0;							\
> +end:											\
> +	;
> +
> +#define LTTNG_SYSCALL_POLL_fds_field								\
> +	sc_in(											\
> +		ctf_custom_field(								\
> +			ctf_custom_type(							\
> +				.atype = atype_sequence_compound,				\
> +				.u.sequence_compound.length_name = "fds_length",		\
> +				.u.sequence_compound.elem_type = &lttng_pollfd_elem,		\
> +			),									\
> +			fds,									\
> +			ctf_custom_code(							\
> +				uint32_t i;							\
> +												\
> +				ctf_align(int) /* Align on largest field in struct. */		\
> +				for (i = 0; i < tp_locvar->fds_length; i++) {			\
> +					ctf_integer_type(int, tp_locvar->fds[i].fd)		\
> +					ctf_integer_type(short, tp_locvar->fds[i].events)	\
> +					ctf_integer_bitfield_type(uint8_t,			\
> +						(uint8_t) tp_locvar->fds[i].events)		\
> +				}								\
> +			)									\
> +		)										\
> +	)											\
> +	sc_out(											\
> +		ctf_custom_field(								\
> +			ctf_custom_type(							\
> +				.atype = atype_sequence_compound,				\
> +				.u.sequence_compound.length_name = "fds_length",		\
> +				.u.sequence_compound.elem_type = &lttng_pollfd_elem,		\
> +			),									\
> +			fds,									\
> +			ctf_custom_code(							\
> +				uint32_t i;							\
> +				unsigned int nr = 0;						\
> +												\
> +				ctf_align(int) /* Align on largest field in struct. */		\
> +				/*								\
> +				 * Iterate over the complete array, but only output		\
> +				 * "ret" active FDs.						\
> +				 */								\
> +				for (i = 0; i < tp_locvar->fds_max_len; i++) {			\
> +					if (!tp_locvar->fds[i].revents)				\
> +						continue;					\
> +					if (nr++ >= tp_locvar->fds_length)			\
> +						break;						\
> +					ctf_integer_type(int, tp_locvar->fds[i].fd)		\
> +					ctf_integer_type(short, tp_locvar->fds[i].revents)	\
> +					ctf_integer_bitfield_type(uint8_t,			\
> +						(uint8_t) tp_locvar->fds[i].revents)		\
> +				}								\
> +				/*								\
> +				 * If there is a discrepancy between ret and the		\
> +				 * content of revents (e.g. caused by userspace corrupting	\
> +				 * the array from a concurrent thread), we have to output	\
> +				 * zeros to keep the trace readable.				\
> +				 */								\
> +				for (i = nr; i < tp_locvar->fds_length; i++) {			\
> +					ctf_integer_type(int, 0)				\
> +					ctf_integer_type(short, 0)				\
> +					ctf_integer_bitfield_type(uint8_t, 0)			\
> +				}								\
> +			)									\
> +		)										\
> +	)
> +
> +#define LTTNG_SYSCALL_POLL_code_post	\
> +	kfree(tp_locvar->fds);
> +
> +#if defined(CONFIG_X86_32) || defined(CONFIG_X86_64)
> +#define OVERRIDE_32_poll
> +#define OVERRIDE_64_poll
> +SC_LTTNG_TRACEPOINT_EVENT_CODE(poll,
> +	TP_PROTO(sc_exit(long ret,) struct pollfd __user * ufds,
> +		unsigned int nfds, int timeout_msecs),
> +	TP_ARGS(sc_exit(ret,) ufds, nfds, timeout_msecs),
> +	TP_locvar(
> +		LTTNG_SYSCALL_POLL_locvar
> +	),
> +	TP_code_pre(
> +		LTTNG_SYSCALL_POLL_code_pre
> +	),
> +	TP_FIELDS(
> +		sc_exit(ctf_integer(long, ret, ret))
> +		sc_in(ctf_integer(int, timeout_msecs, timeout_msecs))
> +		sc_inout(ctf_integer(unsigned int, nfds, nfds))
> +		sc_inout(ctf_integer(unsigned int, fds_length, tp_locvar->fds_length))
> +		sc_in(ctf_integer(uint8_t, overflow, tp_locvar->overflow))
> +		LTTNG_SYSCALL_POLL_fds_field
> +	),
> +	TP_code_post(
> +		LTTNG_SYSCALL_POLL_code_post
> +	)
> +)
> +#endif /* defined(CONFIG_X86_32) || defined(CONFIG_X86_64) */
> +
> +#if defined(CONFIG_X86_32) || defined(CONFIG_X86_64) || defined(CONFIG_ARM64)
> || defined(CONFIG_ARM)
> +#define OVERRIDE_32_ppoll
> +#define OVERRIDE_64_ppoll
> +SC_LTTNG_TRACEPOINT_EVENT_CODE(ppoll,
> +	TP_PROTO(sc_exit(long ret,) struct pollfd __user * ufds,
> +		unsigned int nfds, struct timespec * tsp, const sigset_t * sigmask, size_t
> sigsetsize),
> +	TP_ARGS(sc_exit(ret,) ufds, nfds, tsp, sigmask, sigsetsize),
> +	TP_locvar(
> +		LTTNG_SYSCALL_POLL_locvar
> +	),
> +	TP_code_pre(
> +		LTTNG_SYSCALL_POLL_code_pre
> +	),
> +	TP_FIELDS(
> +		sc_exit(ctf_integer(long, ret, ret))
> +		sc_in(ctf_integer(struct timespec *, tsp, tsp))
> +		sc_in(ctf_integer(const sigset_t *, sigmask, sigmask))
> +		sc_in(ctf_integer(size_t, sigsetsize, sigsetsize))
> +		sc_inout(ctf_integer(unsigned int, nfds, nfds))
> +		sc_inout(ctf_integer(unsigned int, fds_length, tp_locvar->fds_length))
> +		sc_inout(ctf_integer(uint8_t, overflow, tp_locvar->overflow))
> +		LTTNG_SYSCALL_POLL_fds_field
> +	),
> +	TP_code_post(
> +		LTTNG_SYSCALL_POLL_code_post
> +	)
> +)
> +#endif /* defined(CONFIG_X86_32) || defined(CONFIG_X86_64) ||
> defined(CONFIG_ARM64) || defined(CONFIG_ARM) */
> +
> #endif /* CREATE_SYSCALL_TABLE */
> --
> 1.9.1

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com


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