[PATCH] Kprobes: Make kprobe modules more portable

In an effort to make kprobe modules more portable, here is a patch that:

o Introduces the "symbol_name" field to struct kprobe.
  The symbol->address resolution now happens in the kernel in an
  architecture agnostic manner. 64-bit powerpc users no longer have
  to specify the ".symbols"
o Introduces the "offset" field to struct kprobe to allow a user to
  specify an offset into a symbol.
o The legacy mechanism of specifying the kprobe.addr is still supported.
  However, if both the kprobe.addr and kprobe.symbol_name are specified,
  probe registration fails with an -EINVAL.
o The symbol resolution code uses kallsyms_lookup_name(). So
  CONFIG_KPROBES now depends on CONFIG_KALLSYMS
o Apparantly kprobe modules were the only legitimate out-of-tree user of
  the kallsyms_lookup_name() EXPORT. Now that the symbol resolution
  happens in-kernel, remove the EXPORT as suggested by Christoph Hellwig
o Modify tcp_probe.c that uses the kprobe interface so as to make it
  work on multiple platforms (in its earlier form, the code wouldn't
  work, say, on powerpc)

Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: Prasanna S Panchamukhi <prasanna@in.ibm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

10 files changed, 56 insertions, 8 deletions

diff --git a/arch/i386/Kconfig b/arch/i386/Kconfig
index 3fd2f256f2be..af219e51734f 100644
--- a/arch/i386/Kconfig
+++ b/arch/i386/Kconfig
@@ -1142,7 +1142,7 @@ source "arch/i386/oprofile/Kconfig"
 
 config KPROBES
         bool "Kprobes (EXPERIMENTAL)"
-        depends on EXPERIMENTAL && MODULES
+        depends on KALLSYMS && EXPERIMENTAL && MODULES
         help
           Kprobes allows you to trap at almost any kernel address and
           execute a callback function.  register_kprobe() establishes
diff --git a/arch/ia64/Kconfig b/arch/ia64/Kconfig
index 0b7f701d5cf7..70f7eb9fed35 100644
--- a/arch/ia64/Kconfig
+++ b/arch/ia64/Kconfig
@@ -516,7 +516,7 @@ source "arch/ia64/oprofile/Kconfig"
 
 config KPROBES
         bool "Kprobes (EXPERIMENTAL)"
-        depends on EXPERIMENTAL && MODULES
+        depends on KALLSYMS && EXPERIMENTAL && MODULES
         help
           Kprobes allows you to trap at almost any kernel address and
           execute a callback function.  register_kprobe() establishes
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index a0dd1b0ee483..032e6ab5d3c4 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -1069,7 +1069,7 @@ source "arch/powerpc/oprofile/Kconfig"
 
 config KPROBES
         bool "Kprobes (EXPERIMENTAL)"
-        depends on PPC64 && EXPERIMENTAL && MODULES
+        depends on PPC64 && KALLSYMS && EXPERIMENTAL && MODULES
         help
           Kprobes allows you to trap at almost any kernel address and
           execute a callback function.  register_kprobe() establishes
diff --git a/arch/sparc64/Kconfig b/arch/sparc64/Kconfig
index 8d8ca716f7a7..b627f8dbcaad 100644
--- a/arch/sparc64/Kconfig
+++ b/arch/sparc64/Kconfig
@@ -420,7 +420,7 @@ source "arch/sparc64/oprofile/Kconfig"
 
 config KPROBES
         bool "Kprobes (EXPERIMENTAL)"
-        depends on EXPERIMENTAL && MODULES
+        depends on KALLSYMS && EXPERIMENTAL && MODULES
         help
           Kprobes allows you to trap at almost any kernel address and
           execute a callback function.  register_kprobe() establishes
diff --git a/arch/x86_64/Kconfig b/arch/x86_64/Kconfig
index b87a19f0d584..0a5d8e659aa4 100644
--- a/arch/x86_64/Kconfig
+++ b/arch/x86_64/Kconfig
@@ -690,7 +690,7 @@ source "arch/x86_64/oprofile/Kconfig"
 
 config KPROBES
         bool "Kprobes (EXPERIMENTAL)"
-        depends on EXPERIMENTAL && MODULES
+        depends on KALLSYMS && EXPERIMENTAL && MODULES
         help
           Kprobes allows you to trap at almost any kernel address and
           execute a callback function.  register_kprobe() establishes
diff --git a/include/asm-powerpc/kprobes.h b/include/asm-powerpc/kprobes.h
index 34e1f89a5fa0..1ef54be6abfa 100644
--- a/include/asm-powerpc/kprobes.h
+++ b/include/asm-powerpc/kprobes.h
@@ -44,6 +44,21 @@ typedef unsigned int kprobe_opcode_t;
 #define IS_TDI(instr)           (((instr) & 0xfc000000) == 0x08000000)
 #define IS_TWI(instr)           (((instr) & 0xfc000000) == 0x0c000000)
 
+/*
+ * 64bit powerpc uses function descriptors.
+ * Handle cases where:
+ *              - User passes a <.symbol>
+ *              - User passes a <symbol>
+ *              - User passes a non-existant symbol, kallsyms_lookup_name
+ *                returns 0. Don't deref the NULL pointer in that case
+ */
+#define kprobe_lookup_name(name, addr)                                  \
+{                                                                       \
+        addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);           \
+        if (!(name[0] == '.') && addr)                                  \
+                addr = *(kprobe_opcode_t **)addr;                       \
+}
+
 #define JPROBE_ENTRY(pentry)    (kprobe_opcode_t *)((func_descr_t *)pentry)
 
 #define is_trap(instr)  (IS_TW(instr) || IS_TD(instr) || \
diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 8bf6702da2a0..a5c5a0cb0d5c 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -77,6 +77,12 @@ struct kprobe {
         /* location of the probe point */
         kprobe_opcode_t *addr;
 
+        /* Allow user to indicate symbol name of the probe point */
+        char *symbol_name;
+
+        /* Offset into the symbol */
+        unsigned int offset;
+
         /* Called before addr is executed. */
         kprobe_pre_handler_t pre_handler;
 
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index ab16a5a4cfe9..342bca62c496 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -154,7 +154,6 @@ unsigned long kallsyms_lookup_name(const char *name)
         }
         return module_kallsyms_lookup_name(name);
 }
-EXPORT_SYMBOL_GPL(kallsyms_lookup_name);
 
 /*
  * Lookup an address
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 3f57dfdc8f92..f66b8e681b4d 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -37,6 +37,7 @@
 #include <linux/slab.h>
 #include <linux/module.h>
 #include <linux/moduleloader.h>
+#include <linux/kallsyms.h>
 #include <asm-generic/sections.h>
 #include <asm/cacheflush.h>
 #include <asm/errno.h>
@@ -45,6 +46,16 @@
 #define KPROBE_HASH_BITS 6
 #define KPROBE_TABLE_SIZE (1 << KPROBE_HASH_BITS)
 
+
+/*
+ * Some oddball architectures like 64bit powerpc have function descriptors
+ * so this must be overridable.
+ */
+#ifndef kprobe_lookup_name
+#define kprobe_lookup_name(name, addr) \
+        addr = ((kprobe_opcode_t *)(kallsyms_lookup_name(name)))
+#endif
+
 static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
 static struct hlist_head kretprobe_inst_table[KPROBE_TABLE_SIZE];
 static atomic_t kprobe_count;
@@ -447,6 +458,21 @@ static int __kprobes __register_kprobe(struct kprobe *p,
         struct kprobe *old_p;
         struct module *probed_mod;
 
+        /*
+         * If we have a symbol_name argument look it up,
+         * and add it to the address.  That way the addr
+         * field can either be global or relative to a symbol.
+         */
+        if (p->symbol_name) {
+                if (p->addr)
+                        return -EINVAL;
+                kprobe_lookup_name(p->symbol_name, p->addr);
+        }
+
+        if (!p->addr)
+                return -EINVAL;
+        p->addr = (kprobe_opcode_t *)(((char *)p->addr)+ p->offset);
+
         if ((!kernel_text_address((unsigned long) p->addr)) ||
                 in_kprobes_functions((unsigned long) p->addr))
                 return -EINVAL;
diff --git a/net/ipv4/tcp_probe.c b/net/ipv4/tcp_probe.c
index dab37d2f65fc..4be336f17883 100644
--- a/net/ipv4/tcp_probe.c
+++ b/net/ipv4/tcp_probe.c
@@ -99,8 +99,10 @@ static int jtcp_sendmsg(struct kiocb *iocb, struct sock *sk,
 }
 
 static struct jprobe tcp_send_probe = {
-        .kp = { .addr = (kprobe_opcode_t *) &tcp_sendmsg, },
-        .entry = (kprobe_opcode_t *) &jtcp_sendmsg,
+        .kp = {
+                .symbol_name    = "tcp_sendmsg",
+        },
+        .entry  = JPROBE_ENTRY(jtcp_sendmsg),
 };