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Subject[PATCH -tip v9 6/6] perf-probe: Add user memory access attribute support
Date
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.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
Changes in v8
- Fix a typo and rename user field to user_access field. (Thanks Ingo!)
---
tools/perf/Documentation/perf-probe.txt | 3 ++-
tools/perf/util/probe-event.c | 11 +++++++++++
tools/perf/util/probe-event.h | 2 ++
tools/perf/util/probe-file.c | 7 +++++++
tools/perf/util/probe-file.h | 1 +
tools/perf/util/probe-finder.c | 19 ++++++++++++-------
6 files changed, 35 insertions(+), 8 deletions(-)

diff --git a/tools/perf/Documentation/perf-probe.txt b/tools/perf/Documentation/perf-probe.txt
index b6866a05edd2..ed3ecfa422e1 100644
--- a/tools/perf/Documentation/perf-probe.txt
+++ b/tools/perf/Documentation/perf-probe.txt
@@ -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
-----
diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 198e09ff611e..a7ca17be5fc5 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -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';
diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
index 05c8d571a901..96a319cd2378 100644
--- a/tools/perf/util/probe-event.h
+++ b/tools/perf/util/probe-event.h
@@ -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) */
diff --git a/tools/perf/util/probe-file.c b/tools/perf/util/probe-file.c
index 4062bc4412a9..89ce1a9c3798 100644
--- a/tools/perf/util/probe-file.c
+++ b/tools/perf/util/probe-file.c
@@ -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);
+}
diff --git a/tools/perf/util/probe-file.h b/tools/perf/util/probe-file.h
index 2a249182f2a6..986c1c94f64f 100644
--- a/tools/perf/util/probe-file.h
+++ b/tools/perf/util/probe-file.h
@@ -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)
{
diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index c37fbef1711d..c202027716d0 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -294,7 +294,7 @@ static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr,

static int convert_variable_type(Dwarf_Die *vr_die,
struct probe_trace_arg *tvar,
- const char *cast)
+ const char *cast, bool user_access)
{
struct probe_trace_arg_ref **ref_ptr = &tvar->ref;
Dwarf_Die type;
@@ -334,7 +334,8 @@ static int convert_variable_type(Dwarf_Die *vr_die,
pr_debug("%s type is %s.\n",
dwarf_diename(vr_die), dwarf_diename(&type));

- if (cast && strcmp(cast, "string") == 0) { /* String type */
+ if (cast && (!strcmp(cast, "string") || !strcmp(cast, "ustring"))) {
+ /* String type */
ret = dwarf_tag(&type);
if (ret != DW_TAG_pointer_type &&
ret != DW_TAG_array_type) {
@@ -357,6 +358,7 @@ static int convert_variable_type(Dwarf_Die *vr_die,
pr_warning("Out of memory error\n");
return -ENOMEM;
}
+ (*ref_ptr)->user_access = user_access;
}
if (!die_compare_name(&type, "char") &&
!die_compare_name(&type, "unsigned char")) {
@@ -411,7 +413,7 @@ static int convert_variable_type(Dwarf_Die *vr_die,
static int convert_variable_fields(Dwarf_Die *vr_die, const char *varname,
struct perf_probe_arg_field *field,
struct probe_trace_arg_ref **ref_ptr,
- Dwarf_Die *die_mem)
+ Dwarf_Die *die_mem, bool user_access)
{
struct probe_trace_arg_ref *ref = *ref_ptr;
Dwarf_Die type;
@@ -448,6 +450,7 @@ static int convert_variable_fields(Dwarf_Die *vr_die, const char *varname,
*ref_ptr = ref;
}
ref->offset += dwarf_bytesize(&type) * field->index;
+ ref->user_access = user_access;
goto next;
} else if (tag == DW_TAG_pointer_type) {
/* Check the pointer and dereference */
@@ -519,17 +522,18 @@ static int convert_variable_fields(Dwarf_Die *vr_die, const char *varname,
}
}
ref->offset += (long)offs;
+ ref->user_access = user_access;

/* If this member is unnamed, we need to reuse this field */
if (!dwarf_diename(die_mem))
return convert_variable_fields(die_mem, varname, field,
- &ref, die_mem);
+ &ref, die_mem, user_access);

next:
/* Converting next field */
if (field->next)
return convert_variable_fields(die_mem, field->name,
- field->next, &ref, die_mem);
+ field->next, &ref, die_mem, user_access);
else
return 0;
}
@@ -555,11 +559,12 @@ static int convert_variable(Dwarf_Die *vr_die, struct probe_finder *pf)
else if (ret == 0 && pf->pvar->field) {
ret = convert_variable_fields(vr_die, pf->pvar->var,
pf->pvar->field, &pf->tvar->ref,
- &die_mem);
+ &die_mem, pf->pvar->user_access);
vr_die = &die_mem;
}
if (ret == 0)
- ret = convert_variable_type(vr_die, pf->tvar, pf->pvar->type);
+ ret = convert_variable_type(vr_die, pf->tvar, pf->pvar->type,
+ pf->pvar->user_access);
/* *expr will be cached in libdw. Don't free it. */
return ret;
}
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