[Xen-devel] [PATCH v3 5/7] x86/livepatch: Fail the build if duplicate symbols exist

[Andrew Cooper <andrew.cooper3@citrix.com>]

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

The binary diffing algorithm used by xen-livepatch depends on having unique
symbols.

Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>

The livepatch loading algorithm used by Xen resolves relocations by symbol
name, and thus also depends on having unique symbols.

Introduce CONFIG_ENFORCE_UNIQUE_SYMBOLS to control failing the build if
duplicate symbols are found, and disable it in the RANDCONFIG build.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wl@xen.org>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Ross Lagerwall <ross.lagerwall@citrix.com>
CC: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
CC: Norbert Manthey <nmanthey@amazon.de>
CC: Juergen Gross <jgross@suse.com>

v3:
 * Use a new config option
---
 xen/arch/x86/Makefile              |  1 +
 xen/common/Kconfig                 | 18 ++++++++++++++++--
 xen/tools/kconfig/allrandom.config |  1 +
 xen/tools/symbols.c                | 11 +++++++++--
 4 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index 2443fd2cc5..6b369f21cb 100644
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -99,6 +99,7 @@ endif
 
 syms-warn-dup-y := --warn-dup
 syms-warn-dup-$(CONFIG_SUPPRESS_DUPLICATE_SYMBOL_WARNINGS) :=
+syms-warn-dup-$(CONFIG_ENFORCE_UNIQUE_SYMBOLS) := --error-dup
 
 $(TARGET): TMP = $(@D)/.$(@F).elf32
 $(TARGET): $(TARGET)-syms $(efi-y) boot/mkelf32
diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index c9e671869e..4c837d6892 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -361,9 +361,23 @@ config FAST_SYMBOL_LOOKUP
 
 	  If unsure, say Y.
 
+config ENFORCE_UNIQUE_SYMBOLS
+	bool "Enforce unique symbols" if LIVEPATCH
+	default y if LIVEPATCH
+	---help---
+	  Multiple symbols with the same name aren't generally a problem
+	  unless Live patching is to be used.
+
+	  Livepatch loading involves resolving relocations against symbol
+	  names, and attempting to a duplicate symbol in a livepatch will
+	  result in incorrect livepatch application.
+
+	  This option should be used to ensure that a build of Xen can have a
+	  livepatch build and apply correctly.
+
 config SUPPRESS_DUPLICATE_SYMBOL_WARNINGS
-	bool "Suppress duplicate symbol warnings" if !LIVEPATCH
-	default y if !LIVEPATCH
+	bool "Suppress duplicate symbol warnings" if !ENFORCE_UNIQUE_SYMBOLS
+	default y if !ENFORCE_UNIQUE_SYMBOLS
 	---help---
 	  Multiple symbols with the same name aren't generally a problem
 	  unless Live patching is to be used, so these warnings can be
diff --git a/xen/tools/kconfig/allrandom.config b/xen/tools/kconfig/allrandom.config
index 76f74320b5..c480896b96 100644
--- a/xen/tools/kconfig/allrandom.config
+++ b/xen/tools/kconfig/allrandom.config
@@ -2,3 +2,4 @@
 
 CONFIG_GCOV_FORMAT_AUTODETECT=y
 CONFIG_UBSAN=n
+CONFIG_ENFORCE_UNIQUE_SYMBOLS=n
diff --git a/xen/tools/symbols.c b/xen/tools/symbols.c
index 05139d1600..9f9e2c9900 100644
--- a/xen/tools/symbols.c
+++ b/xen/tools/symbols.c
@@ -599,7 +599,7 @@ static int compare_name(const void *p1, const void *p2)
 int main(int argc, char **argv)
 {
 	unsigned int i;
-	bool unsorted = false, warn_dup = false;
+	bool unsorted = false, warn_dup = false, error_dup = false, found_dup = false;
 
 	if (argc >= 2) {
 		for (i = 1; i < argc; i++) {
@@ -619,6 +619,8 @@ int main(int argc, char **argv)
 				sort_by_name = 1;
 			else if (strcmp(argv[i], "--warn-dup") == 0)
 				warn_dup = true;
+			else if (strcmp(argv[i], "--error-dup") == 0)
+				warn_dup = error_dup = true;
 			else if (strcmp(argv[i], "--xensyms") == 0)
 				map_only = true;
 			else
@@ -634,14 +636,19 @@ int main(int argc, char **argv)
 		for (i = 1; i < table_cnt; ++i)
 			if (strcmp(SYMBOL_NAME(table + i - 1),
 				   SYMBOL_NAME(table + i)) == 0 &&
-			    table[i - 1].addr != table[i].addr)
+			    table[i - 1].addr != table[i].addr) {
 				fprintf(stderr,
 					"Duplicate symbol '%s' (%llx != %llx)\n",
 					SYMBOL_NAME(table + i),
 					table[i].addr, table[i - 1].addr);
+				found_dup = true;
+			}
 		unsorted = true;
 	}
 
+	if (error_dup && found_dup)
+		exit(1);
+
 	if (unsorted)
 		qsort(table, table_cnt, sizeof(*table), compare_value);
 
-- 
2.11.0


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