module: trim exception table on init free.

It's theoretically possible that there are exception table entries
which point into the (freed) init text of modules.  These could cause
future problems if other modules get loaded into that memory and cause
an exception as we'd see the wrong fixup.  The only case I know of is
kvm-intel.ko (when CONFIG_CC_OPTIMIZE_FOR_SIZE=n).

Amerigo fixed this long-standing FIXME in the x86 version, but this
patch is more general.

This implements trim_init_extable(); most archs are simple since they
use the standard lib/extable.c sort code.  Alpha and IA64 use relative
addresses in their fixups, so thier trimming is a slight variation.

Sparc32 is unique; it doesn't seem to define ARCH_HAS_SORT_EXTABLE,
yet it defines its own sort_extable() which overrides the one in lib.
It doesn't sort, so we have to mark deleted entries instead of
actually trimming them.

Inspired-by: Amerigo Wang <amwang@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: linux-alpha@vger.kernel.org
Cc: sparclinux@vger.kernel.org
Cc: linux-ia64@vger.kernel.org

diff --git a/arch/alpha/mm/extable.c b/arch/alpha/mm/extable.c
index 62dc379d301af9f1f00e824a2088eb487f77f39f..813c9b63c0e17de3577b5924b54072ad382244d9 100644 (file)
--- a/arch/alpha/mm/extable.c
+++ b/arch/alpha/mm/extable.c
@@ -48,6 +48,27 @@ void sort_extable(struct exception_table_entry *start,
             cmp_ex, swap_ex);
 }
 
+#ifdef CONFIG_MODULES
+/*
+ * Any entry referring to the module init will be at the beginning or
+ * the end.
+ */
+void trim_init_extable(struct module *m)
+{
+       /*trim the beginning*/
+       while (m->num_exentries &&
+              within_module_init(ex_to_addr(&m->extable[0]), m)) {
+               m->extable++;
+               m->num_exentries--;
+       }
+       /*trim the end*/
+       while (m->num_exentries &&
+              within_module_init(ex_to_addr(&m->extable[m->num_exentries-1]),
+                                 m))
+               m->num_exentries--;
+}
+#endif /* CONFIG_MODULES */
+
 const struct exception_table_entry *
 search_extable(const struct exception_table_entry *first,
               const struct exception_table_entry *last,

diff --git a/arch/ia64/mm/extable.c b/arch/ia64/mm/extable.c
index 71c50dd8f8706da65a0362dc2ee8e15888c42060..e95d5ad9285dab575aa10f70e398c1c8368e0316 100644 (file)
--- a/arch/ia64/mm/extable.c
+++ b/arch/ia64/mm/extable.c
@@ -53,6 +53,32 @@ void sort_extable (struct exception_table_entry *start,
             cmp_ex, swap_ex);
 }
 
+static inline unsigned long ex_to_addr(const struct exception_table_entry *x)
+{
+       return (unsigned long)&x->insn + x->insn;
+}
+
+#ifdef CONFIG_MODULES
+/*
+ * Any entry referring to the module init will be at the beginning or
+ * the end.
+ */
+void trim_init_extable(struct module *m)
+{
+       /*trim the beginning*/
+       while (m->num_exentries &&
+              within_module_init(ex_to_addr(&m->extable[0]), m)) {
+               m->extable++;
+               m->num_exentries--;
+       }
+       /*trim the end*/
+       while (m->num_exentries &&
+              within_module_init(ex_to_addr(&m->extable[m->num_exentries-1]),
+                                 m))
+               m->num_exentries--;
+}
+#endif /* CONFIG_MODULES */
+
 const struct exception_table_entry *
 search_extable (const struct exception_table_entry *first,
                const struct exception_table_entry *last,

diff --git a/arch/sparc/include/asm/uaccess_32.h b/arch/sparc/include/asm/uaccess_32.h
index 47d5619d43fafbdd15a0798b4357aac3f30cbce3..8303ac48103426542f6681d826c995f8b8375385 100644 (file)
--- a/arch/sparc/include/asm/uaccess_32.h
+++ b/arch/sparc/include/asm/uaccess_32.h
@@ -17,6 +17,9 @@
 
 #ifndef __ASSEMBLY__
 
+#define ARCH_HAS_SORT_EXTABLE
+#define ARCH_HAS_SEARCH_EXTABLE
+
 /* Sparc is not segmented, however we need to be able to fool access_ok()
  * when doing system calls from kernel mode legitimately.
  *

diff --git a/arch/sparc/mm/extable.c b/arch/sparc/mm/extable.c
index 16cc28935e398ede97a7e86fff652656bd042d21..a61c349448e1e12b28621b3590553593f2d3b799 100644 (file)
--- a/arch/sparc/mm/extable.c
+++ b/arch/sparc/mm/extable.c
@@ -28,6 +28,10 @@ search_extable(const struct exception_table_entry *start,
         *      word 3: last insn address + 4 bytes
         *      word 4: fixup code address
         *
+        * Deleted entries are encoded as:
+        *      word 1: unused
+        *      word 2: -1
+        *
         * See asm/uaccess.h for more details.
         */
 
@@ -39,6 +43,10 @@ search_extable(const struct exception_table_entry *start,
                        continue;
                }
 
+               /* A deleted entry; see trim_init_extable */
+               if (walk->fixup == -1)
+                       continue;
+
                if (walk->insn == value)
                        return walk;
        }
@@ -57,6 +65,27 @@ search_extable(const struct exception_table_entry *start,
         return NULL;
 }
 
+#ifdef CONFIG_MODULES
+/* We could memmove them around; easier to mark the trimmed ones. */
+void trim_init_extable(struct module *m)
+{
+       unsigned int i;
+       bool range;
+
+       for (i = 0; i < m->num_exentries; i += range ? 2 : 1) {
+               range = m->extable[i].fixup == 0;
+
+               if (within_module_init(m->extable[i].insn, m)) {
+                       m->extable[i].fixup = -1;
+                       if (range)
+                               m->extable[i+1].fixup = -1;
+               }
+               if (range)
+                       i++;
+       }
+}
+#endif /* CONFIG_MODULES */
+
 /* Special extable search, which handles ranges.  Returns fixup */
 unsigned long search_extables_range(unsigned long addr, unsigned long *g2)
 {

diff --git a/include/linux/module.h b/include/linux/module.h
index a8f2c0aa4c328af87718285f715bc72b19d7f55f..a7bc6e7b43a7c429b9e4993933a900057034cf77 100644 (file)
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -77,6 +77,7 @@ search_extable(const struct exception_table_entry *first,
 void sort_extable(struct exception_table_entry *start,
                  struct exception_table_entry *finish);
 void sort_main_extable(void);
+void trim_init_extable(struct module *m);
 
 #ifdef MODULE
 #define MODULE_GENERIC_TABLE(gtype,name)                       \

diff --git a/kernel/module.c b/kernel/module.c
index 35f7de00bf0db7aad5b4a34e1311e6157764d331..e4ab36ce767222becc860650e0892399ab58b96d 100644 (file)
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2455,6 +2455,7 @@ SYSCALL_DEFINE3(init_module, void __user *, umod,
        mutex_lock(&module_mutex);
        /* Drop initial reference. */
        module_put(mod);
+       trim_init_extable(mod);
        module_free(mod, mod->module_init);
        mod->module_init = NULL;
        mod->init_size = 0;

diff --git a/lib/extable.c b/lib/extable.c
index 179c0874559569bf2626cbfc70bfcfef09474097..4cac81ec225e09af4cfd69c36d63a574a8418110 100644 (file)
--- a/lib/extable.c
+++ b/lib/extable.c
@@ -39,7 +39,26 @@ void sort_extable(struct exception_table_entry *start,
        sort(start, finish - start, sizeof(struct exception_table_entry),
             cmp_ex, NULL);
 }
-#endif
+
+#ifdef CONFIG_MODULES
+/*
+ * If the exception table is sorted, any referring to the module init
+ * will be at the beginning or the end.
+ */
+void trim_init_extable(struct module *m)
+{
+       /*trim the beginning*/
+       while (m->num_exentries && within_module_init(m->extable[0].insn, m)) {
+               m->extable++;
+               m->num_exentries--;
+       }
+       /*trim the end*/
+       while (m->num_exentries &&
+               within_module_init(m->extable[m->num_exentries-1].insn, m))
+               m->num_exentries--;
+}
+#endif /* CONFIG_MODULES */
+#endif /* !ARCH_HAS_SORT_EXTABLE */
 
 #ifndef ARCH_HAS_SEARCH_EXTABLE
 /*