tracing/probe: Support user-space dereference

Support user-space dereference syntax for probe event arguments
to dereference the data-structure or array in user-space.

The syntax is just adding 'u' before an offset value.

 +|-u<OFFSET>(<FETCHARG>)

e.g. +u8(%ax), +u0(+0(%si))

For example, if you probe do_sched_setscheduler(pid, policy,
param) and record param->sched_priority, you can add new
probe as below;

 p do_sched_setscheduler priority=+u0($arg3)

Note that kprobe event provides this and it doesn't change the
dereference method automatically because we do not know whether
the given address is in userspace or kernel on some archs.

So as same as "ustring", this is an option for user, who has to
carefully choose the dereference method.

Link: http://lkml.kernel.org/r/155789872187.26965.4468456816590888687.stgit@devnote2
Acked-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/Documentation/trace/kprobetrace.rst b/Documentation/trace/kprobetrace.rst
index a3ac7c9ac24241e5bf1bbdea096a8d2940a6d1f6..09ff474493e12a365ce10fbceb09e56cce2dcb07 100644 (file)
--- a/Documentation/trace/kprobetrace.rst
+++ b/Documentation/trace/kprobetrace.rst
@@ -51,7 +51,7 @@ Synopsis of kprobe_events
   $argN                : Fetch the Nth function argument. (N >= 1) (\*1)
   $retval      : Fetch return value.(\*2)
   $comm                : Fetch current task comm.
-  +|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(\*3)
+  +|-[u]OFFS(FETCHARG) : Fetch memory at FETCHARG +|- OFFS address.(\*3)(\*4)
   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
@@ -61,6 +61,7 @@ Synopsis of kprobe_events
   (\*1) only for the probe on function entry (offs == 0).
   (\*2) only for return probe.
   (\*3) this is useful for fetching a field of data structures.
+  (\*4) "u" means user-space dereference. See :ref:`user_mem_access`.
 
 Types
 -----
@@ -79,10 +80,7 @@ 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. "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.
+See :ref:`user_mem_access` for more info..
 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
@@ -97,6 +95,25 @@ Symbol type('symbol') is an alias of u32 or u64 type (depends on BITS_PER_LONG)
 which shows given pointer in "symbol+offset" style.
 For $comm, the default type is "string"; any other type is invalid.
 
+.. _user_mem_access:
+User Memory Access
+------------------
+Kprobe events supports user-space memory access. For that purpose, you can use
+either user-space dereference syntax or 'ustring' type.
+
+The user-space dereference syntax allows you to access a field of a data
+structure in user-space. This is done by adding the "u" prefix to the
+dereference syntax. For example, +u4(%si) means it will read memory from the
+address in the register %si offset by 4, and the memory is expected to be in
+user-space. You can use this for strings too, e.g. +u0(%si):string will read
+a string from the address in the register %si that is expected to be in user-
+space. 'ustring' is a shortcut way of performing the same task. That is,
++0(%si):ustring is equivalent to +u0(%si):string.
+
+Note that kprobe-event provides the user-memory access syntax but it doesn't
+use it transparently. This means if you use normal dereference or string type
+for user memory, it might fail, and may always fail on some archs. The user
+has to carefully check if the target data is in kernel or user space.
 
 Per-Probe Event Filtering
 -------------------------

diff --git a/Documentation/trace/uprobetracer.rst b/Documentation/trace/uprobetracer.rst
index 4346e23e3ae75effc150d9fb33bd3a21de9df1e5..ab13319c66ac10d9d59139f49f7123d5a10e8030 100644 (file)
--- a/Documentation/trace/uprobetracer.rst
+++ b/Documentation/trace/uprobetracer.rst
@@ -42,16 +42,18 @@ Synopsis of uprobe_tracer
    @+OFFSET    : Fetch memory at OFFSET (OFFSET from same file as PATH)
    $stackN     : Fetch Nth entry of stack (N >= 0)
    $stack      : Fetch stack address.
-   $retval     : Fetch return value.(*)
+   $retval     : Fetch return value.(\*1)
    $comm       : Fetch current task comm.
-   +|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(**)
+   +|-[u]OFFS(FETCHARG) : Fetch memory at FETCHARG +|- OFFS address.(\*2)(\*3)
    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.
 
-  (*) only for return probe.
-  (**) this is useful for fetching a field of data structures.
+  (\*1) only for return probe.
+  (\*2) this is useful for fetching a field of data structures.
+  (\*3) Unlike kprobe event, "u" prefix will just be ignored, becuse uprobe
+        events can access only user-space memory.
 
 Types
 -----

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index d3a477a16e7082591e188912a87e93aeb70301b0..6b3b5b0495a89eb8896e563f34d965bdda8062ee 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4842,10 +4842,11 @@ static const char readme_msg[] =
        "\t     args: <name>=fetcharg[:type]\n"
        "\t fetcharg: %<register>, @<address>, @<symbol>[+|-<offset>],\n"
 #ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API
-       "\t           $stack<index>, $stack, $retval, $comm, $arg<N>\n"
+       "\t           $stack<index>, $stack, $retval, $comm, $arg<N>,\n"
 #else
-       "\t           $stack<index>, $stack, $retval, $comm\n"
+       "\t           $stack<index>, $stack, $retval, $comm,\n"
 #endif
+       "\t           +|-[u]<offset>(<fetcharg>)\n"
        "\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>, ustring,\n"
        "\t           <type>\\[<array-size>\\]\n"

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 439bf04d14ce66134e9e0b17ddb438dfc5bc816c..ff14eb011c1c982a904479a543994dca3df83014 100644 (file)
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -952,6 +952,12 @@ probe_mem_read(void *dest, void *src, size_t size)
        return probe_kernel_read(dest, src, size);
 }
 
+static nokprobe_inline int
+probe_mem_read_user(void *dest, void *src, size_t size)
+{
+       return probe_user_read(dest, src, size);
+}
+
 /* Note that we don't verify it, since the code does not come from user space */
 static int
 process_fetch_insn(struct fetch_insn *code, struct pt_regs *regs, void *dest,

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 5a0470f7b9de00caac4912e673ba8b497ca73468..b6b0593844cde765deab726d33c90a811c562b25 100644 (file)
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -324,6 +324,7 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
 {
        struct fetch_insn *code = *pcode;
        unsigned long param;
+       int deref = FETCH_OP_DEREF;
        long offset = 0;
        char *tmp;
        int ret = 0;
@@ -396,9 +397,14 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
                break;
 
        case '+':       /* deref memory */
-               arg++;  /* Skip '+', because kstrtol() rejects it. */
-               /* fall through */
        case '-':
+               if (arg[1] == 'u') {
+                       deref = FETCH_OP_UDEREF;
+                       arg[1] = arg[0];
+                       arg++;
+               }
+               if (arg[0] == '+')
+                       arg++;  /* Skip '+', because kstrtol() rejects it. */
                tmp = strchr(arg, '(');
                if (!tmp) {
                        trace_probe_log_err(offs, DEREF_NEED_BRACE);
@@ -434,7 +440,7 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
                        }
                        *pcode = code;
 
-                       code->op = FETCH_OP_DEREF;
+                       code->op = deref;
                        code->offset = offset;
                }
                break;
@@ -573,14 +579,15 @@ static int traceprobe_parse_probe_arg_body(char *arg, ssize_t *size,
        /* Store operation */
        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) {
+               if (code->op != FETCH_OP_DEREF && code->op != FETCH_OP_UDEREF &&
+                   code->op != FETCH_OP_IMM && code->op != FETCH_OP_COMM) {
                        trace_probe_log_err(offset + (t ? (t - arg) : 0),
                                            BAD_STRING);
                        ret = -EINVAL;
                        goto fail;
                }
-               if (code->op != FETCH_OP_DEREF || parg->count) {
+               if ((code->op == FETCH_OP_IMM || code->op == FETCH_OP_COMM) ||
+                    parg->count) {
                        /*
                         * IMM and COMM is pointing actual address, those must
                         * be kept, and if parg->count != 0, this is an array
@@ -594,7 +601,8 @@ static int traceprobe_parse_probe_arg_body(char *arg, ssize_t *size,
                        }
                }
                /* If op == DEREF, replace it with STRING */
-               if (!strcmp(parg->type->name, "ustring"))
+               if (!strcmp(parg->type->name, "ustring") ||
+                   code->op == FETCH_OP_UDEREF)
                        code->op = FETCH_OP_ST_USTRING;
                else
                        code->op = FETCH_OP_ST_STRING;
@@ -603,6 +611,9 @@ static int traceprobe_parse_probe_arg_body(char *arg, ssize_t *size,
        } else if (code->op == FETCH_OP_DEREF) {
                code->op = FETCH_OP_ST_MEM;
                code->size = parg->type->size;
+       } else if (code->op == FETCH_OP_UDEREF) {
+               code->op = FETCH_OP_ST_UMEM;
+               code->size = parg->type->size;
        } else {
                code++;
                if (code->op != FETCH_OP_NOP) {

diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index c7546e7ff8e24128cac78418af0b43a9d453ba32..42816358dd4826ec629b0701938555a5a6ceb683 100644 (file)
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -92,9 +92,11 @@ enum fetch_op {
        FETCH_OP_FOFFS,         /* File offset: .immediate */
        // Stage 2 (dereference) op
        FETCH_OP_DEREF,         /* Dereference: .offset */
+       FETCH_OP_UDEREF,        /* User-space Dereference: .offset */
        // Stage 3 (store) ops
        FETCH_OP_ST_RAW,        /* Raw: .size */
        FETCH_OP_ST_MEM,        /* Mem: .offset, .size */
+       FETCH_OP_ST_UMEM,       /* Mem: .offset, .size */
        FETCH_OP_ST_STRING,     /* String: .offset, .size */
        FETCH_OP_ST_USTRING,    /* User String: .offset, .size */
        // Stage 4 (modify) op

diff --git a/kernel/trace/trace_probe_tmpl.h b/kernel/trace/trace_probe_tmpl.h
index 2e9e4dae883995f48578fcc164570cdc22fafdcc..e5282828f4a60583e2c471f0c71efdf867969b2c 100644 (file)
--- a/kernel/trace/trace_probe_tmpl.h
+++ b/kernel/trace/trace_probe_tmpl.h
@@ -64,6 +64,8 @@ static nokprobe_inline int
 fetch_store_string_user(unsigned long addr, void *dest, void *base);
 static nokprobe_inline int
 probe_mem_read(void *dest, void *src, size_t size);
+static nokprobe_inline int
+probe_mem_read_user(void *dest, void *src, size_t size);
 
 /* From the 2nd stage, routine is same */
 static nokprobe_inline int
@@ -77,14 +79,21 @@ process_fetch_insn_bottom(struct fetch_insn *code, unsigned long val,
 
 stage2:
        /* 2nd stage: dereference memory if needed */
-       while (code->op == FETCH_OP_DEREF) {
-               lval = val;
-               ret = probe_mem_read(&val, (void *)val + code->offset,
-                                       sizeof(val));
+       do {
+               if (code->op == FETCH_OP_DEREF) {
+                       lval = val;
+                       ret = probe_mem_read(&val, (void *)val + code->offset,
+                                            sizeof(val));
+               } else if (code->op == FETCH_OP_UDEREF) {
+                       lval = val;
+                       ret = probe_mem_read_user(&val,
+                                (void *)val + code->offset, sizeof(val));
+               } else
+                       break;
                if (ret)
                        return ret;
                code++;
-       }
+       } while (1);
 
        s3 = code;
 stage3:
@@ -109,6 +118,9 @@ stage3:
        case FETCH_OP_ST_MEM:
                probe_mem_read(dest, (void *)val + code->offset, code->size);
                break;
+       case FETCH_OP_ST_UMEM:
+               probe_mem_read_user(dest, (void *)val + code->offset, code->size);
+               break;
        case FETCH_OP_ST_STRING:
                loc = *(u32 *)dest;
                ret = fetch_store_string(val + code->offset, dest, base);

diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 852e998051f68f433f23cf2faa0fe8973ad179ef..3d6b868830f3c1e259eeab7f3a0d1f645c3afe6a 100644 (file)
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -140,6 +140,13 @@ probe_mem_read(void *dest, void *src, size_t size)
 
        return copy_from_user(dest, vaddr, size) ? -EFAULT : 0;
 }
+
+static nokprobe_inline int
+probe_mem_read_user(void *dest, void *src, size_t size)
+{
+       return probe_mem_read(dest, src, size);
+}
+
 /*
  * Fetch a null-terminated string. Caller MUST set *(u32 *)dest with max
  * length and relative data location.