[PATCH 1/1] objtool/klp-diff: normalize Module.symvers paths to module names

Module.symvers contains build-tree object paths as module identifiers
(e.g., "arch/x86/kvm/kvm") rather than runtime module names ("kvm").
Objtool's clone_reloc_klp() uses this field directly for exported
symbols, while unexported symbols correctly go through __find_modname().

This means that exported symbol relocations may land in a .klp.rela
section named with the build path rather than the module name.  That is
a crash waiting to happen: the kernel's livepatch loader silently skips
this relocation because it doesn't match the expected klp_object name.
The unresolved relocation sits in the newly activated code, crashing
when executed.

Normalize export->mod at Module.symvers read time using the same logic
as __find_modname() (refactored into a shared normalize_modname()
helper).

Fixes: dd590d4d57eb ("objtool/klp: Introduce klp diff subcommand for diffing object files")
Reported-by: Ben Procknow <[email protected]>
Signed-off-by: Joe Lawrence <[email protected]>
---

Note on the fix and existing gotchas for the review bots: The
normalize_modname() helper is a direct refactoring of the pre-existing
loop in __find_modname().  To keep this critical bug fix short and
safe for stable backporting, I've kept the string manipulation logic
identical to what has already been proven stable in objtool.

 tools/objtool/klp-diff.c | 42 ++++++++++++++++++++++++++++------------
 1 file changed, 30 insertions(+), 12 deletions(-)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index c2c4e4968bc2..2f3b5e69ab2d 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -83,6 +83,32 @@ static char *escape_str(const char *orig)
 	return new;
 }
 
+/*
+ * Convert a build-tree object path to a runtime module name: strip
+ * directory components, replace '-' with '_', and remove file
+ * extensions.  Examples:
+ *
+ *   "arch/x86/kvm/kvm" -> "kvm"
+ *   "arch/x86/kvm/kvm-intel" -> "kvm_intel".
+ *
+ * Used by read_exports() to normalize Module.symvers entries and by
+ * __find_modname() as a fallback when .modinfo lacks a "name=" tag.
+ */
+static char *normalize_modname(char *name)
+{
+	for (char *c = name; *c; c++) {
+		if (*c == '/')
+			name = c + 1;
+		else if (*c == '-')
+			*c = '_';
+		else if (*c == '.') {
+			*c = '\0';
+			break;
+		}
+	}
+	return name;
+}
+
 static int read_exports(void)
 {
 	const char *symvers = "Module.symvers";
@@ -150,6 +176,9 @@ static int read_exports(void)
 			return -1;
 		}
 
+		if (strcmp(export->mod, "vmlinux"))
+			export->mod = normalize_modname(export->mod);
+
 		export->sym = strdup(sym);
 		if (!export->sym) {
 			ERROR_GLIBC("strdup");
@@ -790,18 +819,7 @@ static const char *__find_modname(struct elfs *e)
 		return NULL;
 	}
 
-	for (char *c = name; *c; c++) {
-		if (*c == '/')
-			name = c + 1;
-		else if (*c == '-')
-			*c = '_';
-		else if (*c == '.') {
-			*c = '\0';
-			break;
-		}
-	}
-
-	return name;
+	return normalize_modname(name);
 }
 
 /* Get the object's module name as defined by the kernel (and klp_object) */
-- 
2.54.0