[PATCH v7 12/24] 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>
Reviewed-by: Andrew Cooper <andrew.cooper3@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.
v6: Rebase where the spinlock is no more recursive. Drop the spinlock
    usage in xsplice_symbols_lookup_by_name
v7: Add Andrew's Reviewed-by
    Initialize addr and symname to zero as xensyms_read uses it.
---
---
 xen/arch/x86/Makefile               |  16 +++-
 xen/arch/x86/test/Makefile          |   4 +-
 xen/arch/x86/test/xen_hello_world.c |   5 +-
 xen/common/symbols.c                |  34 ++++++++
 xen/common/xsplice.c                | 156 +++++++++++++++++++++++++++++++++++-
 xen/common/xsplice_elf.c            |  19 ++++-
 xen/include/xen/symbols.h           |   2 +
 xen/include/xen/xsplice.h           |   8 ++
 8 files changed, 232 insertions(+), 12 deletions(-)

diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index 6c2d5fa..57c93e1 100644
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -72,6 +72,12 @@ efi-y := $(shell if [ ! -r $(BASEDIR)/include/xen/compile.h -o \
                       -O $(BASEDIR)/include/xen/compile.h ]; then \
                          echo '$(TARGET).efi'; fi)
 
+ifdef CONFIG_XSPLICE
+all_symbols = --all-symbols
+else
+all_symbols =
+endif
+
 $(TARGET): $(TARGET)-syms $(efi-y) boot/mkelf32
 	./boot/mkelf32 $(TARGET)-syms $(TARGET) 0x100000 \
 	`$(NM) -nr $(TARGET)-syms | head -n 1 | sed -e 's/^\([^ ]*\).*/0x\1/'`
@@ -111,12 +117,14 @@ $(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 $@
@@ -140,14 +148,14 @@ $(TARGET).efi: prelink-efi.o efi.lds efi/relocs-dummy.o $(BASEDIR)/common/symbol
 	                $(BASEDIR)/common/symbols-dummy.o -o $(@D)/.$(@F).$(base).0 &&) :
 	$(guard) efi/mkreloc $(foreach base,$(VIRT_BASE) $(ALT_BASE),$(@D)/.$(@F).$(base).0) >$(@D)/.$(@F).0r.S
 	$(guard) $(NM) -pa --format=sysv $(@D)/.$(@F).$(VIRT_BASE).0 \
-		| $(guard) $(BASEDIR)/tools/symbols --sysv --sort >$(@D)/.$(@F).0s.S
+		| $(guard) $(BASEDIR)/tools/symbols $(all_symbols) --sysv --sort >$(@D)/.$(@F).0s.S
 	$(guard) $(MAKE) -f $(BASEDIR)/Rules.mk $(@D)/.$(@F).0r.o $(@D)/.$(@F).0s.o
 	$(foreach base, $(VIRT_BASE) $(ALT_BASE), \
 	          $(guard) $(LD) $(call EFI_LDFLAGS,$(base)) -T efi.lds -N $< \
 	                $(@D)/.$(@F).0r.o $(@D)/.$(@F).0s.o -o $(@D)/.$(@F).$(base).1 &&) :
 	$(guard) efi/mkreloc $(foreach base,$(VIRT_BASE) $(ALT_BASE),$(@D)/.$(@F).$(base).1) >$(@D)/.$(@F).1r.S
 	$(guard) $(NM) -pa --format=sysv $(@D)/.$(@F).$(VIRT_BASE).1 \
-		| $(guard) $(BASEDIR)/tools/symbols --sysv --sort >$(@D)/.$(@F).1s.S
+		| $(guard) $(BASEDIR)/tools/symbols $(all_symbols) --sysv --sort >$(@D)/.$(@F).1s.S
 	$(guard) $(MAKE) -f $(BASEDIR)/Rules.mk $(@D)/.$(@F).1r.o $(@D)/.$(@F).1s.o
 	$(guard) $(LD) $(call EFI_LDFLAGS,$(VIRT_BASE)) -T efi.lds -N $< \
 	                $(@D)/.$(@F).1r.o $(@D)/.$(@F).1s.o -o $@
diff --git a/xen/arch/x86/test/Makefile b/xen/arch/x86/test/Makefile
index b9cf13c..baa4820 100644
--- a/xen/arch/x86/test/Makefile
+++ b/xen/arch/x86/test/Makefile
@@ -26,14 +26,12 @@ clean::
 # the last entry in the build target.
 #
 .PHONY: config.h
-config.h: OLD_CODE=$(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 21831e9..22fe2e7 100644
--- a/xen/arch/x86/test/xen_hello_world.c
+++ b/xen/arch/x86/test/xen_hello_world.c
@@ -10,11 +10,14 @@
 static char hello_world_patch_this_fnc[] = "xen_extra_version";
 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 = {
     .version = XSPLICE_PAYLOAD_VERSION,
     .name = hello_world_patch_this_fnc,
     .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 b18ddcd1..781765d 100644
--- a/xen/common/symbols.c
+++ b/xen/common/symbols.c
@@ -207,3 +207,37 @@ int xensyms_read(uint32_t *symnum, char *type,
 
     return 0;
 }
+
+unsigned long symbols_lookup_by_name(const char *symname)
+{
+    char name[KSYM_NAME_LEN + 1] = { 0 };
+    uint32_t symnum = 0;
+    char type;
+    uint64_t addr = 0;
+    int rc;
+
+    if ( symname == '\0' )
+        return 0;
+
+    do {
+        rc = xensyms_read(&symnum, &type, &addr, name);
+        if ( rc )
+           break;
+
+        if ( !strcmp(name, symname) )
+            return addr;
+
+    } while ( name[0] != '\0' );
+
+    return 0;
+}
+
+/*
+ * 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 9a53cf4..27f4822 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>
@@ -51,6 +52,9 @@ struct payload {
     struct list_head applied_list;       /* Linked to 'applied_list'. */
     struct xsplice_patch_func_internal *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. */
 };
 
@@ -114,6 +118,28 @@ static int verify_payload(const xen_sysctl_xsplice_upload_t *upload, char *n)
     return 0;
 }
 
+unsigned long xsplice_symbols_lookup_by_name(const char *symname)
+{
+    struct payload *data;
+
+    ASSERT(spin_is_locked(&payload_lock));
+    list_for_each_entry ( data, &payload_list, list )
+    {
+        unsigned int i;
+
+        for ( i = 0; i < data->nsyms; i++ )
+        {
+            if ( !data->symtab[i].new_symbol )
+                continue;
+
+            if ( !strcmp(data->symtab[i].name, symname) )
+                return data->symtab[i].value;
+        }
+    }
+
+    return 0;
+}
+
 static struct payload *find_payload(const char *name)
 {
     struct payload *data, *found = NULL;
@@ -376,11 +402,129 @@ static int prepare_payload(struct payload *payload,
         for ( j = 0; j < ARRAY_SIZE(f->u.pad); j++ )
             if ( f->u.pad[j] )
                 return -EINVAL;
+
+        /* Lookup function's old address if not already resolved. */
+        if ( !f->old_addr )
+        {
+            f->old_addr = (void *)symbols_lookup_by_name(f->name);
+            if ( !f->old_addr )
+            {
+                f->old_addr = (void *)xsplice_symbols_lookup_by_name(f->name);
+                if ( !f->old_addr )
+                {
+                    printk(XENLOG_DEBUG XSPLICE "%s: Could not resolve old address of %s\n",
+                           elf->name, f->name);
+                    return -ENOENT;
+                }
+            }
+            dprintk(XENLOG_DEBUG, XSPLICE "%s: Resolved old address %s => %p\n",
+                    elf->name, f->name, f->old_addr);
+        }
     }
 
     return 0;
 }
 
+static bool_t is_payload_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_payload_symbol(elf, elf->sym + i) )
+        {
+            nsyms++;
+            strtab_len += strlen(elf->sym[i].name) + 1;
+        }
+    }
+
+    symtab = xmalloc_array(struct xsplice_symbol, nsyms);
+    strtab = xmalloc_array(char, strtab_len);
+
+    if ( !strtab || !symtab )
+    {
+        xfree(strtab);
+        xfree(symtab);
+        return -ENOMEM;
+    }
+
+    nsyms = 0;
+    strtab_len = 0;
+    for ( i = 1; i < elf->nsym; i++ )
+    {
+        if ( is_payload_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 == (unsigned long)payload->funcs[j].new_addr )
+            {
+                found = 1;
+                break;
+            }
+        }
+
+        if ( !found )
+        {
+            if ( xsplice_symbols_lookup_by_name(symtab[i].name) )
+            {
+                printk(XENLOG_DEBUG XSPLICE "%s: duplicate new symbol: %s\n",
+                       elf->name, symtab[i].name);
+                xfree(symtab);
+                xfree(strtab);
+                return -EEXIST;
+            }
+            symtab[i].new_symbol = 1;
+            dprintk(XENLOG_DEBUG, XSPLICE "%s: new symbol %s\n",
+                     elf->name, symtab[i].name);
+        }
+        else
+        {
+            /* new_symbol is not set. */
+            dprintk(XENLOG_DEBUG, XSPLICE "%s: overriding symbol %s\n",
+                    elf->name, symtab[i].name);
+        }
+    }
+
+    payload->symtab = symtab;
+    payload->strtab = strtab;
+    payload->nsyms = nsyms;
+
+    return 0;
+}
+
 static void free_payload(struct payload *data)
 {
     ASSERT(spin_is_locked(&payload_lock));
@@ -388,6 +532,8 @@ static void free_payload(struct payload *data)
     payload_cnt--;
     payload_version++;
     free_payload_data(data);
+    xfree(data->symtab);
+    xfree(data->strtab);
     xfree(data);
 }
 
@@ -420,6 +566,10 @@ static int load_payload_data(struct payload *payload, void *raw, size_t len)
     if ( rc )
         goto out;
 
+    rc = build_symbol_table(payload, &elf);
+    if ( rc )
+        goto out;
+
     rc = secure_payload(payload, &elf);
 
  out:
@@ -491,8 +641,12 @@ static int xsplice_upload(xen_sysctl_xsplice_upload_t *upload)
 
     vfree(raw_data);
 
-    if ( rc )
+    if ( rc && data )
+    {
+        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 7262fc2..09b8c93 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>
 
@@ -274,9 +275,21 @@ int xsplice_elf_resolve_symbols(struct xsplice_elf *elf)
             break;
 
         case SHN_UNDEF:
-            printk(XENLOG_DEBUG XSPLICE "%s: Unknown symbol: %s\n",
-                   elf->name, elf->sym[i].name);
-            rc = -ENOENT;
+            elf->sym[i].sym->st_value = (unsigned long)symbols_lookup_by_name(elf->sym[i].name);
+            if ( !elf->sym[i].sym->st_value )
+            {
+                elf->sym[i].sym->st_value = (unsigned long)
+                        xsplice_symbols_lookup_by_name(elf->sym[i].name);
+                if ( !elf->sym[i].sym->st_value )
+                {
+                    printk(XENLOG_DEBUG XSPLICE "%s: Unknown symbol: %s\n",
+                           elf->name, elf->sym[i].name);
+                    rc = -ENOENT;
+                    break;
+                }
+            }
+            dprintk(XENLOG_DEBUG, XSPLICE "%s: Undefined symbol resolved: %s => %#"PRIxElfAddr"\n",
+                    elf->name, elf->sym[i].name, elf->sym[i].sym->st_value);
             break;
 
         case SHN_ABS:
diff --git a/xen/include/xen/symbols.h b/xen/include/xen/symbols.h
index f58e611..d9bd35f 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);
 
+unsigned long 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 8486887..a0436da 100644
--- a/xen/include/xen/xsplice.h
+++ b/xen/include/xen/xsplice.h
@@ -57,8 +57,16 @@ struct xsplice_patch_func_internal {
 /* Convenience define for printk. */
 #define XSPLICE "xsplice: "
 
+struct xsplice_symbol {
+    const char *name;
+    uint64_t value;
+    size_t size;
+    bool_t new_symbol;
+};
+
 int xsplice_op(struct xen_sysctl_xsplice_op *);
 void check_for_xsplice_work(void);
+unsigned long xsplice_symbols_lookup_by_name(const char *symname);
 
 /* Arch hooks. */
 int arch_xsplice_verify_elf(const struct xsplice_elf *elf);
-- 
2.5.0


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