[Xen-devel] [PATCH v6 15/24] xsplice: Add support for exception tables.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

From: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>

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.

Also we add an test-case to make sure we have an exception that
is handled.

To not grow the code-base if xSplice is not compiled in we add
certain #define to help in determining if code needs to be __init
or not.

Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

---
Cc: Keir Fraser <keir@xxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

v3:
 - s/module/payload/
 - sanity checks.
 - Move code around.
 - s/module/payload/
v4: Use 'struct virtual_region'
v5:
  - Expand test-case.
  - Deal with struct exception_table_entry being const.
v6:
 - Make the code have __init if not compiled with xSplice
 - Remove not needed declarations.
---
---
 xen/arch/x86/extable.c                   | 31 ++++++++++++++++++-------------
 xen/arch/x86/test/xen_hello_world_func.c | 11 +++++++++++
 xen/common/xsplice.c                     | 25 +++++++++++++++++++++++++
 xen/include/asm-x86/uaccess.h            |  2 ++
 xen/include/xen/xsplice.h                | 17 +++++++++++++++++
 5 files changed, 73 insertions(+), 13 deletions(-)

diff --git a/xen/arch/x86/extable.c b/xen/arch/x86/extable.c
index 4184ad8..33a917c 100644
--- a/xen/arch/x86/extable.c
+++ b/xen/arch/x86/extable.c
@@ -7,6 +7,7 @@
 #include <xen/spinlock.h>
 #include <asm/uaccess.h>
 #include <xen/virtual_region.h>
+#include <xen/xsplice.h>
 
 #define EX_FIELD(ptr, field) ((unsigned long)&(ptr)->field + (ptr)->field)
 
@@ -20,7 +21,7 @@ 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 __INIT cmp_ex(const void *a, const void *b)
 {
        const struct exception_table_entry *l = a, *r = b;
        unsigned long lip = ex_addr(l);
@@ -35,7 +36,7 @@ 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 __INIT swap_ex(void *a, void *b, int size)
 {
        struct exception_table_entry *l = a, *r = b, tmp;
        long delta = b - a;
@@ -48,19 +49,23 @@ static void __init swap_ex(void *a, void *b, int size)
 }
 #endif
 
-void __init sort_exception_tables(void)
+void __INIT 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;
@@ -85,7 +90,7 @@ search_exception_table(unsigned long addr)
     const struct virtual_region *region = find_text_region(addr);
 
     if ( region && region->ex )
-        return search_one_table(region->ex, region->ex_end-1, addr);
+        return search_one_extable(region->ex, region->ex_end-1, addr);
 
     return 0;
 }
@@ -94,7 +99,7 @@ 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/arch/x86/test/xen_hello_world_func.c 
b/xen/arch/x86/test/xen_hello_world_func.c
index 1ad002a..7e239ca 100644
--- a/xen/arch/x86/test/xen_hello_world_func.c
+++ b/xen/arch/x86/test/xen_hello_world_func.c
@@ -5,9 +5,20 @@
 
 #include <xen/types.h>
 
+static unsigned long *non_canonical_addr = (unsigned long *)(1UL<<48);
+
 /* Our replacement function for xen_extra_version. */
 const char *xen_hello_world(void)
 {
+    unsigned long tmp = 0xdeadbeef;
+    int rc;
+    /*
+     * Any BUG, or WARN_ON will contain symbol and payload name. Furthermore
+     * exceptions will be caught and processed properly.
+     */
+    rc = __get_user(tmp, non_canonical_addr);
+    BUG_ON(rc != -EFAULT);
+
     return "Hello World";
 }
 
diff --git a/xen/common/xsplice.c b/xen/common/xsplice.c
index 087cb94..31ddd5d 100644
--- a/xen/common/xsplice.c
+++ b/xen/common/xsplice.c
@@ -525,6 +525,31 @@ static int prepare_payload(struct payload *payload,
                                       sizeof(*region->frame[i].bugs);
     }
 
+#ifdef CONFIG_X86
+    sec = xsplice_elf_sec_by_name(elf, ".ex_table");
+    if ( sec )
+    {
+        struct exception_table_entry *s, *e;
+
+        if ( !sec->sec->sh_size ||
+             (sec->sec->sh_size % sizeof(*region->ex)) )
+        {
+            dprintk(XENLOG_DEBUG, XSPLICE "%s: Wrong size of .ex_table 
(exp:%lu vs %lu)!\n",
+                    elf->name, sizeof(*region->ex),
+                    sec->sec->sh_size);
+            return -EINVAL;
+        }
+
+        s = sec->load_addr;
+        e = sec->load_addr + sec->sec->sh_size;
+
+        sort_exception_table(s ,e);
+
+        region->ex = (const struct exception_table_entry *)s;
+        region->ex_end = (const struct exception_table_entry *)e;
+    }
+#endif
+
     return 0;
 }
 
diff --git a/xen/include/asm-x86/uaccess.h b/xen/include/asm-x86/uaccess.h
index 947470d..2c839a9 100644
--- a/xen/include/asm-x86/uaccess.h
+++ b/xen/include/asm-x86/uaccess.h
@@ -277,5 +277,7 @@ extern struct exception_table_entry __stop___pre_ex_table[];
 
 extern unsigned long search_exception_table(unsigned long);
 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 ca78eae..6113061 100644
--- a/xen/include/xen/xsplice.h
+++ b/xen/include/xen/xsplice.h
@@ -37,6 +37,15 @@ struct xsplice_patch_func_internal {
     } u;
 };
 
+/*
+ * We use alternative and exception table code - which by default are __init
+ * only, however we need them during runtime. These macros allows us to build
+ * the image with these functions built-in. (See the #else below).
+ */
+#define __INITCONST
+#define __INITDATA
+#define __INIT
+
 /* Convenience define for printk. */
 #define XSPLICE "xsplice: "
 
@@ -96,6 +105,14 @@ void arch_xsplice_mask(void);
 void arch_xsplice_unmask(void);
 #else
 
+/*
+ * If not compiling with xSplice certain functionality should stay as
+ * __init.
+ */
+#define __INITCONST    __initconst
+#define __INITDATA     __initdata
+#define __INIT         __init
+
 #include <xen/errno.h> /* For -EOPNOTSUPP */
 static inline int xsplice_op(struct xen_sysctl_xsplice_op *op)
 {
-- 
2.5.0


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