[PATCH v2 12/13] xsplice: Add support for exception tables. (v2)

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

From: Ross Lagerwall <ross.lagerwall@citrix.com>

Add support for exception tables contained within xSplice payloads. If an
exception occurs search either the main exception table or a particular
active payload's exception table depending on the instruction pointer.

Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
v2:
 - s/module/payload/
 - sanity checks.
---
 xen/arch/x86/extable.c        | 36 +++++++++++++++++++++--------------
 xen/common/xsplice.c          | 44 +++++++++++++++++++++++++++++++++++++++++++
 xen/include/asm-x86/uaccess.h |  5 +++++
 xen/include/xen/xsplice.h     |  5 +++++
 4 files changed, 76 insertions(+), 14 deletions(-)

diff --git a/xen/arch/x86/extable.c b/xen/arch/x86/extable.c
index 89b5bcb..2787a92 100644
--- a/xen/arch/x86/extable.c
+++ b/xen/arch/x86/extable.c
@@ -4,6 +4,7 @@
 #include <xen/perfc.h>
 #include <xen/sort.h>
 #include <xen/spinlock.h>
+#include <xen/xsplice.h>
 #include <asm/uaccess.h>
 
 #define EX_FIELD(ptr, field) ((unsigned long)&(ptr)->field + (ptr)->field)
@@ -18,7 +19,7 @@ static inline unsigned long ex_cont(const struct exception_table_entry *x)
 	return EX_FIELD(x, cont);
 }
 
-static int __init cmp_ex(const void *a, const void *b)
+static int cmp_ex(const void *a, const void *b)
 {
 	const struct exception_table_entry *l = a, *r = b;
 	unsigned long lip = ex_addr(l);
@@ -33,7 +34,7 @@ static int __init cmp_ex(const void *a, const void *b)
 }
 
 #ifndef swap_ex
-static void __init swap_ex(void *a, void *b, int size)
+static void swap_ex(void *a, void *b, int size)
 {
 	struct exception_table_entry *l = a, *r = b, tmp;
 	long delta = b - a;
@@ -46,19 +47,23 @@ static void __init swap_ex(void *a, void *b, int size)
 }
 #endif
 
-void __init sort_exception_tables(void)
+void sort_exception_table(struct exception_table_entry *start,
+                          struct exception_table_entry *stop)
 {
-    sort(__start___ex_table, __stop___ex_table - __start___ex_table,
-         sizeof(struct exception_table_entry), cmp_ex, swap_ex);
-    sort(__start___pre_ex_table,
-         __stop___pre_ex_table - __start___pre_ex_table,
+    sort(start, stop - start,
          sizeof(struct exception_table_entry), cmp_ex, swap_ex);
 }
 
-static inline unsigned long
-search_one_table(const struct exception_table_entry *first,
-                 const struct exception_table_entry *last,
-                 unsigned long value)
+void __init sort_exception_tables(void)
+{
+    sort_exception_table(__start___ex_table, __stop___ex_table);
+    sort_exception_table(__start___pre_ex_table, __stop___pre_ex_table);
+}
+
+unsigned long
+search_one_extable(const struct exception_table_entry *first,
+                   const struct exception_table_entry *last,
+                   unsigned long value)
 {
     const struct exception_table_entry *mid;
     long diff;
@@ -80,15 +85,18 @@ search_one_table(const struct exception_table_entry *first,
 unsigned long
 search_exception_table(unsigned long addr)
 {
-    return search_one_table(
-        __start___ex_table, __stop___ex_table-1, addr);
+    if ( likely(is_kernel(addr)) )
+        return search_one_extable(
+            __start___ex_table, __stop___ex_table-1, addr);
+    else
+        return search_module_extables(addr);
 }
 
 unsigned long
 search_pre_exception_table(struct cpu_user_regs *regs)
 {
     unsigned long addr = (unsigned long)regs->eip;
-    unsigned long fixup = search_one_table(
+    unsigned long fixup = search_one_extable(
         __start___pre_ex_table, __stop___pre_ex_table-1, addr);
     if ( fixup )
     {
diff --git a/xen/common/xsplice.c b/xen/common/xsplice.c
index 02cb4a8..53a67a9 100644
--- a/xen/common/xsplice.c
+++ b/xen/common/xsplice.c
@@ -47,6 +47,10 @@ struct payload {
     size_t core_text_size;               /* Everything else - .data,.rodata, etc. */
     struct bug_frame *start_bug_frames[BUGFRAME_NR]; /* .bug.frame patching. */
     struct bug_frame *stop_bug_frames[BUGFRAME_NR];
+#ifdef CONFIG_X86
+    struct exception_table_entry *start_ex_table;
+    struct exception_table_entry *stop_ex_table;
+#endif
     char name[XEN_XSPLICE_NAME_SIZE + 1];/* Name of it. */
 };
 
@@ -668,6 +672,20 @@ static int find_special_sections(struct payload *payload,
         payload->start_bug_frames[i] = (struct bug_frame *)sec->load_addr;
         payload->stop_bug_frames[i] = (struct bug_frame *)(sec->load_addr + sec->sec->sh_size);
     }
+#ifdef CONFIG_X86
+    sec = xsplice_elf_sec_by_name(elf, ".ex_table");
+    if ( sec )
+    {
+        if ( ( !sec->sec->sh_size ) ||
+             ( sec->sec->sh_size % sizeof *sec->load_addr ) )
+            return -EINVAL;
+
+        payload->start_ex_table = (struct exception_table_entry *)sec->load_addr;
+        payload->stop_ex_table = (struct exception_table_entry *)(sec->load_addr + sec->sec->sh_size);
+
+        sort_exception_table(payload->start_ex_table, payload->stop_ex_table);
+    }
+#endif
     return 0;
 }
 
@@ -1029,6 +1047,32 @@ bool_t is_active_module_text(unsigned long addr)
     return 0;
 }
 
+#ifdef CONFIG_X86
+unsigned long search_module_extables(unsigned long addr)
+{
+    struct payload *data;
+    unsigned long ret;
+
+    /* No locking since this list is only ever changed during apply or revert
+     * context. */
+    list_for_each_entry ( data, &applied_list, applied_list )
+    {
+        if ( !data->start_ex_table )
+            continue;
+        if ( !((void *)addr >= data->payload_address &&
+               (void *)addr < (data->payload_address + data->core_text_size)))
+            continue;
+
+        ret = search_one_extable(data->start_ex_table, data->stop_ex_table - 1,
+                                 addr);
+        if ( ret )
+            return ret;
+    }
+
+    return 0;
+}
+#endif
+
 static int __init xsplice_init(void)
 {
     register_keyhandler('x', xsplice_printall, "print xsplicing info", 1);
diff --git a/xen/include/asm-x86/uaccess.h b/xen/include/asm-x86/uaccess.h
index 947470d..9e67bf0 100644
--- a/xen/include/asm-x86/uaccess.h
+++ b/xen/include/asm-x86/uaccess.h
@@ -276,6 +276,11 @@ extern struct exception_table_entry __start___pre_ex_table[];
 extern struct exception_table_entry __stop___pre_ex_table[];
 
 extern unsigned long search_exception_table(unsigned long);
+extern unsigned long search_one_extable(const struct exception_table_entry *first,
+                                        const struct exception_table_entry *last,
+                                        unsigned long value);
 extern void sort_exception_tables(void);
+extern void sort_exception_table(struct exception_table_entry *start,
+                                 struct exception_table_entry *stop);
 
 #endif /* __X86_UACCESS_H__ */
diff --git a/xen/include/xen/xsplice.h b/xen/include/xen/xsplice.h
index 41b738a..ec929fd 100644
--- a/xen/include/xen/xsplice.h
+++ b/xen/include/xen/xsplice.h
@@ -29,6 +29,7 @@ void do_xsplice(void);
 struct bug_frame *xsplice_find_bug(const char *eip, int *id);
 bool_t is_module(const void *addr);
 bool_t is_active_module_text(unsigned long addr);
+unsigned long search_module_extables(unsigned long addr);
 #else
 static inline void do_xsplice(void) { };
 static inline struct bug_frame *xsplice_find_bug(const char *eip, int *id)
@@ -43,6 +44,10 @@ static inline bool_t is_active_module_text(unsigned long addr)
 {
 	return 0;
 }
+static inline unsigned long search_module_extables(unsigned long addr)
+{
+	return 0;
+}
 #endif
 
 /* Arch hooks */
-- 
2.1.0