Commit 88903c46 authored by Masami Hiramatsu's avatar Masami Hiramatsu Committed by Steven Rostedt (VMware)
Browse files

tracing/probe: Add ustring type for user-space string 

Add "ustring" type for fetching user-space string from kprobe event.
User can specify ustring type at uprobe event, and it is same as
"string" for uprobe.

Note that probe-event provides this option but it doesn't choose the
correct type automatically since we have not way to decide the address
is in user-space or not on some arch (and on some other arch, you can
fetch the string by "string" type). So user must carefully check the
target code (e.g. if you see __user on the target variable) and
use this new type.

Link: http://lkml.kernel.org/r/155789871009.26965.14167558859557329331.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 3d708182

Documentation/trace/kprobetrace.rst

+7 −2
Original line number Diff line number Diff line
@@ -55,7 +55,8 @@ Synopsis of kprobe_events 
  NAME=FETCHARG : Set NAME as the argument name of FETCHARG.

  FETCHARG:TYPE : Set TYPE as the type of FETCHARG. Currently, basic types

		  (u8/u16/u32/u64/s8/s16/s32/s64), hexadecimal types

		  (x8/x16/x32/x64), "string" and bitfield are supported.

		  (x8/x16/x32/x64), "string", "ustring" and bitfield

		  are supported.



  (\*1) only for the probe on function entry (offs == 0).

  (\*2) only for return probe.
@@ -77,7 +78,11 @@ apply it to registers/stack-entries etc. (for example, '$stack1:x8[8]' is 
wrong, but '+8($stack):x8[8]' is OK.)

String type is a special type, which fetches a "null-terminated" string from

kernel space. This means it will fail and store NULL if the string container

has been paged out.

has been paged out. "ustring" type is an alternative of string for user-space.

Note that kprobe-event provides string/ustring types, but doesn't change it

automatically. So user has to decide if the targe string in kernel or in user

space carefully. On some arch, if you choose wrong one, it always fails to

record string data.

The string array type is a bit different from other types. For other base

types, <base-type>[1] is equal to <base-type> (e.g. +0(%di):x32[1] is same

as +0(%di):x32.) But string[1] is not equal to string. The string type itself

kernel/trace/trace.c

+1 −1
Original line number Diff line number Diff line
@@ -4847,7 +4847,7 @@ static const char readme_msg[] = 
	"\t           $stack<index>, $stack, $retval, $comm\n"

#endif

	"\t     type: s8/16/32/64, u8/16/32/64, x8/16/32/64, string, symbol,\n"

	"\t           b<bit-width>@<bit-offset>/<container-size>,\n"

	"\t           b<bit-width>@<bit-offset>/<container-size>, ustring,\n"

	"\t           <type>\\[<array-size>\\]\n"

#ifdef CONFIG_HIST_TRIGGERS

	"\t    field: <stype> <name>;\n"

kernel/trace/trace_kprobe.c

+39 −3
Original line number Diff line number Diff line
@@ -886,6 +886,15 @@ fetch_store_strlen(unsigned long addr) 
	return (ret < 0) ? ret : len;

}



/* Return the length of string -- including null terminal byte */

static nokprobe_inline int

fetch_store_strlen_user(unsigned long addr)

{

	const void __user *uaddr =  (__force const void __user *)addr;



	return strnlen_unsafe_user(uaddr, MAX_STRING_SIZE);

}



/*

 * Fetch a null-terminated string. Caller MUST set *(u32 *)buf with max

 * length and relative data location.
@@ -894,19 +903,46 @@ static nokprobe_inline int 
fetch_store_string(unsigned long addr, void *dest, void *base)

{

	int maxlen = get_loc_len(*(u32 *)dest);

	u8 *dst = get_loc_data(dest, base);

	void *__dest;

	long ret;



	if (unlikely(!maxlen))

		return -ENOMEM;



	__dest = get_loc_data(dest, base);



	/*

	 * Try to get string again, since the string can be changed while

	 * probing.

	 */

	ret = strncpy_from_unsafe(dst, (void *)addr, maxlen);

	ret = strncpy_from_unsafe(__dest, (void *)addr, maxlen);

	if (ret >= 0)

		*(u32 *)dest = make_data_loc(ret, __dest - base);



	return ret;

}



/*

 * Fetch a null-terminated string from user. Caller MUST set *(u32 *)buf

 * with max length and relative data location.

 */

static nokprobe_inline int

fetch_store_string_user(unsigned long addr, void *dest, void *base)

{

	const void __user *uaddr =  (__force const void __user *)addr;

	int maxlen = get_loc_len(*(u32 *)dest);

	void *__dest;

	long ret;



	if (unlikely(!maxlen))

		return -ENOMEM;



	__dest = get_loc_data(dest, base);



	ret = strncpy_from_unsafe_user(__dest, uaddr, maxlen);

	if (ret >= 0)

		*(u32 *)dest = make_data_loc(ret, (void *)dst - base);

		*(u32 *)dest = make_data_loc(ret, __dest - base);



	return ret;

}

kernel/trace/trace_probe.c

+11 −3
Original line number Diff line number Diff line
@@ -78,6 +78,8 @@ static const struct fetch_type probe_fetch_types[] = { 
	/* Special types */

	__ASSIGN_FETCH_TYPE("string", string, string, sizeof(u32), 1,

			    "__data_loc char[]"),

	__ASSIGN_FETCH_TYPE("ustring", string, string, sizeof(u32), 1,

			    "__data_loc char[]"),

	/* Basic types */

	ASSIGN_FETCH_TYPE(u8,  u8,  0),

	ASSIGN_FETCH_TYPE(u16, u16, 0),
@@ -569,7 +571,8 @@ static int traceprobe_parse_probe_arg_body(char *arg, ssize_t *size, 
		goto fail;



	/* Store operation */

	if (!strcmp(parg->type->name, "string")) {

	if (!strcmp(parg->type->name, "string") ||

	    !strcmp(parg->type->name, "ustring")) {

		if (code->op != FETCH_OP_DEREF && code->op != FETCH_OP_IMM &&

		    code->op != FETCH_OP_COMM) {

			trace_probe_log_err(offset + (t ? (t - arg) : 0),
@@ -590,7 +593,11 @@ static int traceprobe_parse_probe_arg_body(char *arg, ssize_t *size, 
				goto fail;

			}

		}

		code->op = FETCH_OP_ST_STRING;	/* In DEREF case, replace it */

		/* If op == DEREF, replace it with STRING */

		if (!strcmp(parg->type->name, "ustring"))

			code->op = FETCH_OP_ST_USTRING;

		else

			code->op = FETCH_OP_ST_STRING;

		code->size = parg->type->size;

		parg->dynamic = true;

	} else if (code->op == FETCH_OP_DEREF) {
@@ -618,7 +625,8 @@ static int traceprobe_parse_probe_arg_body(char *arg, ssize_t *size, 
	/* Loop(Array) operation */

	if (parg->count) {

		if (scode->op != FETCH_OP_ST_MEM &&

		    scode->op != FETCH_OP_ST_STRING) {

		    scode->op != FETCH_OP_ST_STRING &&

		    scode->op != FETCH_OP_ST_USTRING) {

			trace_probe_log_err(offset + (t ? (t - arg) : 0),

					    BAD_STRING);

			ret = -EINVAL;

kernel/trace/trace_probe.h

+1 −0
Original line number Diff line number Diff line
@@ -96,6 +96,7 @@ enum fetch_op { 
	FETCH_OP_ST_RAW,	/* Raw: .size */

	FETCH_OP_ST_MEM,	/* Mem: .offset, .size */

	FETCH_OP_ST_STRING,	/* String: .offset, .size */

	FETCH_OP_ST_USTRING,	/* User String: .offset, .size */

	// Stage 4 (modify) op

	FETCH_OP_MOD_BF,	/* Bitfield: .basesize, .lshift, .rshift */

	// Stage 5 (loop) op

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