[PATCH v5 13/28] xsplice, symbols: Implement symbol name resolution on address.

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

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

If in the payload we do not have the old_addr we can resolve
the virtual address based on the UNDEFined symbols.

We also use an boolean flag: new_symbol to track symbols. The usual
case this is used is by:

* A payload may introduce a new symbol
* A payload may override an existing symbol (introduced in Xen or another
  payload)
* Overriding symbols must exist in the symtab for backtraces.
* A payload must always link against the object which defines the new symbol.

Considering that payloads may be loaded in any order it would be incorrect to
link against a payload which simply overrides a symbol because you could end
up with a chain of jumps which is inefficient and may result in the expected
function not being executed.

Also we include a local definition block in the symbols.c file.

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

---
Cc: Keir Fraser <keir@xen.org>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>

v1: Ross original version.
v2: Include test-case and document update.
v2: s/size_t/ssize_t/
    Include core_text_size, core_text calculation
v4: Cast on dprintk to uint64_t to make ELF 32bit build.
---
 xen/arch/x86/Makefile               |   6 +-
 xen/arch/x86/test/Makefile          |   4 +-
 xen/arch/x86/test/xen_hello_world.c |   5 +-
 xen/common/symbols.c                |  33 ++++++++
 xen/common/xsplice.c                | 160 ++++++++++++++++++++++++++++++++++++
 xen/common/xsplice_elf.c            |  21 ++++-
 xen/include/xen/symbols.h           |   2 +
 xen/include/xen/xsplice.h           |   8 ++
 8 files changed, 229 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index d9416d1..a1ef24b 100644
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -113,12 +113,14 @@ $(TARGET)-syms: prelink.o xen.lds $(BASEDIR)/common/symbols-dummy.o
 	$(LD) $(LDFLAGS) -T xen.lds -N prelink.o \
 	    $(BASEDIR)/common/symbols-dummy.o -o $(@D)/.$(@F).0
 	$(NM) -pa --format=sysv $(@D)/.$(@F).0 \
-		| $(BASEDIR)/tools/symbols --sysv --sort >$(@D)/.$(@F).0.S
+		| $(BASEDIR)/tools/symbols --all-symbols --sysv --sort \
+		>$(@D)/.$(@F).0.S
 	$(MAKE) -f $(BASEDIR)/Rules.mk $(@D)/.$(@F).0.o
 	$(LD) $(LDFLAGS) -T xen.lds -N prelink.o \
 	    $(@D)/.$(@F).0.o -o $(@D)/.$(@F).1
 	$(NM) -pa --format=sysv $(@D)/.$(@F).1 \
-		| $(BASEDIR)/tools/symbols --sysv --sort --warn-dup >$(@D)/.$(@F).1.S
+		| $(BASEDIR)/tools/symbols --all-symbols --sysv --sort --warn-dup \
+		>$(@D)/.$(@F).1.S
 	$(MAKE) -f $(BASEDIR)/Rules.mk $(@D)/.$(@F).1.o
 	$(LD) $(LDFLAGS) -T xen.lds -N prelink.o \
 	    $(@D)/.$(@F).1.o -o $@
diff --git a/xen/arch/x86/test/Makefile b/xen/arch/x86/test/Makefile
index 7a364c1..22fcb14 100644
--- a/xen/arch/x86/test/Makefile
+++ b/xen/arch/x86/test/Makefile
@@ -35,14 +35,12 @@ clean::
 # the last entry in the build target.
 #
 .PHONY: config.h
-config.h: OLD_CODE=$(call CODE_ADDR,$(BASEDIR)/xen-syms,xen_extra_version)
 config.h: OLD_CODE_SZ=$(call CODE_SZ,$(BASEDIR)/xen-syms,xen_extra_version)
 config.h: NEW_CODE_SZ=$(call CODE_SZ,$<,xen_hello_world)
 config.h: xen_hello_world_func.o
 	(set -e; \
 	 echo "#define NEW_CODE_SZ $(NEW_CODE_SZ)"; \
-	 echo "#define OLD_CODE_SZ $(OLD_CODE_SZ)"; \
-	 echo "#define OLD_CODE $(OLD_CODE)") > $@
+	 echo "#define OLD_CODE_SZ $(OLD_CODE_SZ)") > $@
 
 .PHONY: xsplice
 xsplice: config.h
diff --git a/xen/arch/x86/test/xen_hello_world.c b/xen/arch/x86/test/xen_hello_world.c
index f6ac098..243eb3f 100644
--- a/xen/arch/x86/test/xen_hello_world.c
+++ b/xen/arch/x86/test/xen_hello_world.c
@@ -11,10 +11,13 @@
 static char xen_hello_world_name[] = "xen_hello_world";
 extern const char *xen_hello_world(void);
 
+/* External symbol. */
+extern const char *xen_extra_version(void);
+
 struct xsplice_patch_func __section(".xsplice.funcs") xsplice_xen_hello_world = {
     .name = xen_hello_world_name,
     .new_addr = (unsigned long)(xen_hello_world),
-    .old_addr = OLD_CODE,
+    .old_addr = (unsigned long)(xen_extra_version),
     .new_size = NEW_CODE_SZ,
     .old_size = OLD_CODE_SZ,
 };
diff --git a/xen/common/symbols.c b/xen/common/symbols.c
index 92fb0ee..329eba2 100644
--- a/xen/common/symbols.c
+++ b/xen/common/symbols.c
@@ -207,3 +207,36 @@ int xensyms_read(uint32_t *symnum, char *type,
 
     return 0;
 }
+
+uint64_t symbols_lookup_by_name(const char *symname)
+{
+    uint32_t symnum = 0;
+    uint64_t addr = 0, outaddr = 0;
+    int rc;
+    char type;
+    char name[KSYM_NAME_LEN + 1] = {0};
+
+    do {
+        rc = xensyms_read(&symnum, &type, &addr, name);
+        if ( rc )
+            break;
+
+        if ( !strcmp(name, symname) )
+        {
+            outaddr = addr;
+            break;
+        }
+    } while ( name[0] != '\0' );
+
+    return outaddr;
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/common/xsplice.c b/xen/common/xsplice.c
index a0d7fe0..24100e7 100644
--- a/xen/common/xsplice.c
+++ b/xen/common/xsplice.c
@@ -14,6 +14,7 @@
 #include <xen/smp.h>
 #include <xen/softirq.h>
 #include <xen/spinlock.h>
+#include <xen/symbols.h>
 #include <xen/vmap.h>
 #include <xen/wait.h>
 #include <xen/xsplice_elf.h>
@@ -54,6 +55,9 @@ struct payload {
     struct list_head applied_list;       /* Linked to 'applied_list'. */
     struct xsplice_patch_func *funcs;    /* The array of functions to patch. */
     unsigned int nfuncs;                 /* Nr of functions to patch. */
+    struct xsplice_symbol *symtab;       /* All symbols. */
+    char *strtab;                        /* Pointer to .strtab. */
+    unsigned int nsyms;                  /* Nr of entries in .strtab and symbols. */
     char name[XEN_XSPLICE_NAME_SIZE];    /* Name of it. */
 };
 
@@ -107,6 +111,34 @@ static int verify_payload(const xen_sysctl_xsplice_upload_t *upload)
     return 0;
 }
 
+uint64_t xsplice_symbols_lookup_by_name(const char *symname)
+{
+    struct payload *data;
+    unsigned int i;
+    uint64_t value = 0;
+
+    spin_lock_recursive(&payload_lock);
+
+    list_for_each_entry ( data, &payload_list, list )
+    {
+        for ( i = 0; i < data->nsyms; i++ )
+        {
+            if ( !data->symtab[i].new_symbol )
+                continue;
+
+            if ( !strcmp(data->symtab[i].name, symname) )
+            {
+                value = data->symtab[i].value;
+                goto out;
+            }
+        }
+    }
+
+out:
+    spin_unlock_recursive(&payload_lock);
+    return value;
+}
+
 /*
  * We may be holding the payload_lock or not. Hence we need
  * the recursive spinlock. Or we can judiciously use an
@@ -397,8 +429,126 @@ static int prepare_payload(struct payload *payload,
         for ( j = 0; j < 24; j++ )
             if ( f->pad[j] )
                 return -EINVAL;
+
+        /* Lookup function's old address if not already resolved. */
+        if ( !f->old_addr )
+        {
+            f->old_addr = symbols_lookup_by_name(f->name);
+            if ( !f->old_addr )
+            {
+                f->old_addr = xsplice_symbols_lookup_by_name(f->name);
+                if ( !f->old_addr )
+                {
+                    printk(XENLOG_ERR "%s%s: Could not resolve old address of %s\n",
+                           XSPLICE, elf->name, f->name);
+                    return -ENOENT;
+                }
+            }
+            dprintk(XENLOG_DEBUG, "%s%s: Resolved old address %s => 0x%"PRIx64"\n",
+                   XSPLICE, elf->name, f->name, f->old_addr);
+        }
+    }
+
+    return 0;
+}
+
+static bool_t is_core_symbol(const struct xsplice_elf *elf,
+                             const struct xsplice_elf_sym *sym)
+{
+    if ( sym->sym->st_shndx == SHN_UNDEF ||
+         sym->sym->st_shndx >= elf->hdr->e_shnum )
+        return 0;
+
+    return !!( (elf->sec[sym->sym->st_shndx].sec->sh_flags & SHF_ALLOC) &&
+               (ELF64_ST_TYPE(sym->sym->st_info) == STT_OBJECT ||
+                ELF64_ST_TYPE(sym->sym->st_info) == STT_FUNC) );
+}
+
+static int build_symbol_table(struct payload *payload,
+                              const struct xsplice_elf *elf)
+{
+    unsigned int i, j, nsyms = 0;
+    size_t strtab_len = 0;
+    struct xsplice_symbol *symtab;
+    char *strtab;
+
+    ASSERT(payload->nfuncs);
+
+    /* Recall that section @0 is always NULL. */
+    for ( i = 1; i < elf->nsym; i++ )
+    {
+        if ( is_core_symbol(elf, elf->sym + i) )
+        {
+            nsyms++;
+            strtab_len += strlen(elf->sym[i].name) + 1;
+        }
+    }
+
+    symtab = xmalloc_array(struct xsplice_symbol, nsyms);
+    if ( !symtab )
+        return -ENOMEM;
+
+    strtab = xmalloc_bytes(strtab_len);
+    if ( !strtab )
+    {
+        xfree(symtab);
+        return -ENOMEM;
+    }
+
+    nsyms = 0;
+    strtab_len = 0;
+    for ( i = 1; i < elf->nsym; i++ )
+    {
+        if ( is_core_symbol(elf, elf->sym + i) )
+        {
+            symtab[nsyms].name = strtab + strtab_len;
+            symtab[nsyms].size = elf->sym[i].sym->st_size;
+            symtab[nsyms].value = elf->sym[i].sym->st_value;
+            symtab[nsyms].new_symbol = 0; /* To be checked below. */
+            strtab_len += strlcpy(strtab + strtab_len, elf->sym[i].name,
+                                  KSYM_NAME_LEN) + 1;
+            nsyms++;
+        }
+    }
+
+    for ( i = 0; i < nsyms; i++ )
+    {
+        bool_t found = 0;
+
+        for ( j = 0; j < payload->nfuncs; j++ )
+        {
+            if ( symtab[i].value == payload->funcs[j].new_addr )
+            {
+                found = 1;
+                break;
+            }
+        }
+
+        if ( !found )
+        {
+            if ( xsplice_symbols_lookup_by_name(symtab[i].name) )
+            {
+                printk(XENLOG_ERR "%s%s: duplicate new symbol: %s\n",
+                       XSPLICE, elf->name, symtab[i].name);
+                xfree(symtab);
+                xfree(strtab);
+                return -EEXIST;
+            }
+            symtab[i].new_symbol = 1;
+            dprintk(XENLOG_DEBUG, "%s%s: new symbol %s\n",
+                    XSPLICE, elf->name, symtab[i].name);
+        }
+        else
+        {
+            dprintk(XENLOG_DEBUG, "%s%s: overriding symbol %s\n",
+                    XSPLICE, elf->name, symtab[i].name);
+        }
     }
 
+    payload->symtab = symtab;
+    payload->strtab = strtab;
+    payload->nsyms = nsyms;
+
     return 0;
 }
 
@@ -410,6 +560,8 @@ static void free_payload(struct payload *data)
     payload_cnt--;
     payload_version++;
     free_payload_data(data);
+    xfree(data->symtab);
+    xfree(data->strtab);
     xfree(data);
 }
 
@@ -450,6 +602,10 @@ static int load_payload_data(struct payload *payload, void *raw, ssize_t len)
     if ( rc )
         goto out;
 
+    rc = build_symbol_table(payload, &elf);
+    if ( rc )
+        goto out;
+
     rc = secure_payload(payload, &elf);
 
  out:
@@ -517,7 +673,11 @@ static int xsplice_upload(xen_sysctl_xsplice_upload_t *upload)
  out:
     vfree(raw_data);
     if ( rc )
+    {
+        xfree(data->symtab);
+        xfree(data->strtab);
         xfree(data);
+    }
 
     return rc;
 }
diff --git a/xen/common/xsplice_elf.c b/xen/common/xsplice_elf.c
index e5c0b12..248e3f3 100644
--- a/xen/common/xsplice_elf.c
+++ b/xen/common/xsplice_elf.c
@@ -4,6 +4,7 @@
 
 #include <xen/errno.h>
 #include <xen/lib.h>
+#include <xen/symbols.h>
 #include <xen/xsplice_elf.h>
 #include <xen/xsplice.h>
 
@@ -235,15 +236,27 @@ int xsplice_elf_resolve_symbols(struct xsplice_elf *elf)
                 break;
 
             case SHN_UNDEF:
-                printk(XENLOG_ERR "%s%s: Unknown symbol: %s\n",
-                       XSPLICE, elf->name, elf->sym[i].name);
-                return -ENOENT;
+                elf->sym[i].sym->st_value = symbols_lookup_by_name(elf->sym[i].name);
+                if ( !elf->sym[i].sym->st_value )
+                {
+                    elf->sym[i].sym->st_value =
+                        xsplice_symbols_lookup_by_name(elf->sym[i].name);
+                    if ( !elf->sym[i].sym->st_value )
+                    {
+                        printk(XENLOG_ERR "%s%s: Unknown symbol: %s\n",
+                               XSPLICE, elf->name, elf->sym[i].name);
+                        return -ENOENT;
+                    }
+                }
+                dprintk(XENLOG_DEBUG, "%s%s: Undefined symbol resolved: %s => 0x%"PRIx64"\n",
+                       XSPLICE, elf->name, elf->sym[i].name,
+                       (uint64_t)elf->sym[i].sym->st_value);
                 break;
 
             case SHN_ABS:
                 dprintk(XENLOG_DEBUG, "%s%s: Absolute symbol: %s => 0x%"PRIx64"\n",
                       XSPLICE, elf->name, elf->sym[i].name,
-                      elf->sym[i].sym->st_value);
+                      (uint64_t)elf->sym[i].sym->st_value);
                 break;
 
             default:
diff --git a/xen/include/xen/symbols.h b/xen/include/xen/symbols.h
index f58e611..d679aa9 100644
--- a/xen/include/xen/symbols.h
+++ b/xen/include/xen/symbols.h
@@ -23,4 +23,6 @@ const char *symbols_lookup(unsigned long addr,
 int xensyms_read(uint32_t *symnum, char *type,
                  uint64_t *address, char *name);
 
+uint64_t symbols_lookup_by_name(const char *symname);
+
 #endif /*_XEN_SYMBOLS_H*/
diff --git a/xen/include/xen/xsplice.h b/xen/include/xen/xsplice.h
index 00b3cb2..8bc55f3 100644
--- a/xen/include/xen/xsplice.h
+++ b/xen/include/xen/xsplice.h
@@ -33,8 +33,16 @@ struct xsplice_patch_func {
 /* Convenience define for printk. */
 #define XSPLICE "xsplice: "
 
+struct xsplice_symbol {
+    const char *name;
+    uint64_t value;
+    ssize_t size;
+    bool_t new_symbol;
+};
+
 int xsplice_op(struct xen_sysctl_xsplice_op *);
 void check_for_xsplice_work(void);
+uint64_t xsplice_symbols_lookup_by_name(const char *symname);
 
 /* Arch hooks. */
 int arch_xsplice_verify_elf(const struct xsplice_elf *elf, void *data);
-- 
2.5.0


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