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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH v5 13/28] xsplice, symbols: Implement symbol name resolution on address.
From: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
---
Cc: Keir Fraser <keir@xxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
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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