Commit 1e032f7c authored by Masami Hiramatsu's avatar Masami Hiramatsu Committed by Steven Rostedt (VMware)
Browse files

perf-probe: Add user memory access attribute support 

Add user memory access attribute for kprobe event arguments.
If a given 'local variable' is in user-space, User can
specify memory access method by '@user' suffix. This is
not only for string but also for data structure.

If we access a field of data structure in user memory from
kernel on some arch, it will fail. e.g.

 perf probe -a "sched_setscheduler param->sched_priority"

This will fail to access the "param->sched_priority" because
the param is __user pointer. Instead, we can now specify
@user suffix for such argument.

 perf probe -a "sched_setscheduler param->sched_priority@user"

Note that kernel memory access with "@user" must always fail
on any arch.

Link: http://lkml.kernel.org/r/155789874562.26965.10836126971405890891.stgit@devnote2



Acked-by: default avatarIngo Molnar <mingo@kernel.org>
Signed-off-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent bdf2b8cb

tools/perf/Documentation/perf-probe.txt

+2 −1
Original line number Diff line number Diff line
@@ -194,12 +194,13 @@ PROBE ARGUMENT 
--------------

Each probe argument follows below syntax.



 [NAME=]LOCALVAR|$retval|%REG|@SYMBOL[:TYPE]

 [NAME=]LOCALVAR|$retval|%REG|@SYMBOL[:TYPE][@user]



'NAME' specifies the name of this argument (optional). You can use the name of local variable, local data structure member (e.g. var->field, var.field2), local array with fixed index (e.g. array[1], var->array[0], var->pointer[2]), or kprobe-tracer argument format (e.g. $retval, %ax, etc). Note that the name of this argument will be set as the last member name if you specify a local data structure member (e.g. field2 for 'var->field1.field2'.)

'$vars' and '$params' special arguments are also available for NAME, '$vars' is expanded to the local variables (including function parameters) which can access at given probe point. '$params' is expanded to only the function parameters.

'TYPE' casts the type of this argument (optional). If omitted, perf probe automatically set the type based on debuginfo (*). Currently, basic types (u8/u16/u32/u64/s8/s16/s32/s64), hexadecimal integers (x/x8/x16/x32/x64), signedness casting (u/s), "string" and bitfield are supported. (see TYPES for detail)

On x86 systems %REG is always the short form of the register: for example %AX. %RAX or %EAX is not valid.

"@user" is a special attribute which means the LOCALVAR will be treated as a user-space memory. This is only valid for kprobe event.



TYPES

-----

tools/perf/util/probe-event.c

+11 −0
Original line number Diff line number Diff line
@@ -1577,6 +1577,17 @@ static int parse_perf_probe_arg(char *str, struct perf_probe_arg *arg) 
		str = tmp + 1;

	}



	tmp = strchr(str, '@');

	if (tmp && tmp != str && strcmp(tmp + 1, "user")) { /* user attr */

		if (!user_access_is_supported()) {

			semantic_error("ftrace does not support user access\n");

			return -EINVAL;

		}

		*tmp = '\0';

		arg->user_access = true;

		pr_debug("user_access ");

	}



	tmp = strchr(str, ':');

	if (tmp) {	/* Type setting */

		*tmp = '\0';

tools/perf/util/probe-event.h

+2 −0
Original line number Diff line number Diff line
@@ -37,6 +37,7 @@ struct probe_trace_point { 
struct probe_trace_arg_ref {

	struct probe_trace_arg_ref	*next;	/* Next reference */

	long				offset;	/* Offset value */

	bool				user_access;	/* User-memory access */

};



/* kprobe-tracer and uprobe-tracer tracing argument */
@@ -82,6 +83,7 @@ struct perf_probe_arg { 
	char				*var;	/* Variable name */

	char				*type;	/* Type name */

	struct perf_probe_arg_field	*field;	/* Structure fields */

	bool				user_access;	/* User-memory access */

};



/* Perf probe probing event (point + arg) */

tools/perf/util/probe-file.c

+7 −0
Original line number Diff line number Diff line
@@ -1015,6 +1015,7 @@ enum ftrace_readme { 
	FTRACE_README_PROBE_TYPE_X = 0,

	FTRACE_README_KRETPROBE_OFFSET,

	FTRACE_README_UPROBE_REF_CTR,

	FTRACE_README_USER_ACCESS,

	FTRACE_README_END,

};
@@ -1027,6 +1028,7 @@ static struct { 
	DEFINE_TYPE(FTRACE_README_PROBE_TYPE_X, "*type: * x8/16/32/64,*"),

	DEFINE_TYPE(FTRACE_README_KRETPROBE_OFFSET, "*place (kretprobe): *"),

	DEFINE_TYPE(FTRACE_README_UPROBE_REF_CTR, "*ref_ctr_offset*"),

	DEFINE_TYPE(FTRACE_README_USER_ACCESS, "*[u]<offset>*"),

};



static bool scan_ftrace_readme(enum ftrace_readme type)
@@ -1087,3 +1089,8 @@ bool uprobe_ref_ctr_is_supported(void) 
{

	return scan_ftrace_readme(FTRACE_README_UPROBE_REF_CTR);

}



bool user_access_is_supported(void)

{

	return scan_ftrace_readme(FTRACE_README_USER_ACCESS);

}

tools/perf/util/probe-file.h

+1 −0
Original line number Diff line number Diff line
@@ -70,6 +70,7 @@ int probe_cache__show_all_caches(struct strfilter *filter); 
bool probe_type_is_available(enum probe_type type);

bool kretprobe_offset_is_supported(void);

bool uprobe_ref_ctr_is_supported(void);

bool user_access_is_supported(void);

#else	/* ! HAVE_LIBELF_SUPPORT */

static inline struct probe_cache *probe_cache__new(const char *tgt __maybe_unused, struct nsinfo *nsi __maybe_unused)

{

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