Merge tag 'livepatching-for-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/livepatching/livepatching

Pull livepatching updates from Petr Mladek:

 - Allow reloading a livepatched module by clearing livepatch-specific
   relocations in the livepatch module.

   Otherwise, the repeated load would fail on consistency checks.

* tag 'livepatching-for-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/livepatching/livepatching:
  livepatch,x86: Clear relocation targets on a module removal
  x86/module: remove unused code in __apply_relocate_add

1 files changed, 60 insertions, 37 deletions

diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
index 705fb2a41d7d..84ad0e61ba6e 100644
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -129,22 +129,27 @@ int apply_relocate(Elf32_Shdr *sechdrs,
 	return 0;
 }
 #else /*X86_64*/
-static int __apply_relocate_add(Elf64_Shdr *sechdrs,
+static int __write_relocate_add(Elf64_Shdr *sechdrs,
 		   const char *strtab,
 		   unsigned int symindex,
 		   unsigned int relsec,
 		   struct module *me,
-		   void *(*write)(void *dest, const void *src, size_t len))
+		   void *(*write)(void *dest, const void *src, size_t len),
+		   bool apply)
 {
 	unsigned int i;
 	Elf64_Rela *rel = (void *)sechdrs[relsec].sh_addr;
 	Elf64_Sym *sym;
 	void *loc;
 	u64 val;
+	u64 zero = 0ULL;
 
-	DEBUGP("Applying relocate section %u to %u\n",
+	DEBUGP("%s relocate section %u to %u\n",
+	       apply ? "Applying" : "Clearing",
 	       relsec, sechdrs[relsec].sh_info);
 	for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rel); i++) {
+		size_t size;
+
 		/* This is where to make the change */
 		loc = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
 			+ rel[i].r_offset;
@@ -162,56 +167,53 @@ static int __apply_relocate_add(Elf64_Shdr *sechdrs,
 
 		switch (ELF64_R_TYPE(rel[i].r_info)) {
 		case R_X86_64_NONE:
-			break;
+			continue;  /* nothing to write */
 		case R_X86_64_64:
-			if (*(u64 *)loc != 0)
-				goto invalid_relocation;
-			write(loc, &val, 8);
+			size = 8;
 			break;
 		case R_X86_64_32:
-			if (*(u32 *)loc != 0)
-				goto invalid_relocation;
-			write(loc, &val, 4);
-			if (val != *(u32 *)loc)
+			if (val != *(u32 *)&val)
 				goto overflow;
+			size = 4;
 			break;
 		case R_X86_64_32S:
-			if (*(s32 *)loc != 0)
-				goto invalid_relocation;
-			write(loc, &val, 4);
-			if ((s64)val != *(s32 *)loc)
+			if ((s64)val != *(s32 *)&val)
 				goto overflow;
+			size = 4;
 			break;
 		case R_X86_64_PC32:
 		case R_X86_64_PLT32:
-			if (*(u32 *)loc != 0)
-				goto invalid_relocation;
 			val -= (u64)loc;
-			write(loc, &val, 4);
-#if 0
-			if ((s64)val != *(s32 *)loc)
-				goto overflow;
-#endif
+			size = 4;
 			break;
 		case R_X86_64_PC64:
-			if (*(u64 *)loc != 0)
-				goto invalid_relocation;
 			val -= (u64)loc;
-			write(loc, &val, 8);
+			size = 8;
 			break;
 		default:
 			pr_err("%s: Unknown rela relocation: %llu\n",
 			       me->name, ELF64_R_TYPE(rel[i].r_info));
 			return -ENOEXEC;
 		}
+
+		if (apply) {
+			if (memcmp(loc, &zero, size)) {
+				pr_err("x86/modules: Invalid relocation target, existing value is nonzero for type %d, loc %p, val %Lx\n",
+				       (int)ELF64_R_TYPE(rel[i].r_info), loc, val);
+				return -ENOEXEC;
+			}
+			write(loc, &val, size);
+		} else {
+			if (memcmp(loc, &val, size)) {
+				pr_warn("x86/modules: Invalid relocation target, existing value does not match expected value for type %d, loc %p, val %Lx\n",
+					(int)ELF64_R_TYPE(rel[i].r_info), loc, val);
+				return -ENOEXEC;
+			}
+			write(loc, &zero, size);
+		}
 	}
 	return 0;
 
-invalid_relocation:
-	pr_err("x86/modules: Skipping invalid relocation target, existing value is nonzero for type %d, loc %p, val %Lx\n",
-	       (int)ELF64_R_TYPE(rel[i].r_info), loc, val);
-	return -ENOEXEC;
-
 overflow:
 	pr_err("overflow in relocation type %d val %Lx\n",
 	       (int)ELF64_R_TYPE(rel[i].r_info), val);
@@ -220,11 +222,12 @@ overflow:
 	return -ENOEXEC;
 }
 
-int apply_relocate_add(Elf64_Shdr *sechdrs,
-		   const char *strtab,
-		   unsigned int symindex,
-		   unsigned int relsec,
-		   struct module *me)
+static int write_relocate_add(Elf64_Shdr *sechdrs,
+			      const char *strtab,
+			      unsigned int symindex,
+			      unsigned int relsec,
+			      struct module *me,
+			      bool apply)
 {
 	int ret;
 	bool early = me->state == MODULE_STATE_UNFORMED;
@@ -235,8 +238,8 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
 		mutex_lock(&text_mutex);
 	}
 
-	ret = __apply_relocate_add(sechdrs, strtab, symindex, relsec, me,
-				   write);
+	ret = __write_relocate_add(sechdrs, strtab, symindex, relsec, me,
+				   write, apply);
 
 	if (!early) {
 		text_poke_sync();
@@ -246,6 +249,26 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
 	return ret;
 }
 
+int apply_relocate_add(Elf64_Shdr *sechdrs,
+		   const char *strtab,
+		   unsigned int symindex,
+		   unsigned int relsec,
+		   struct module *me)
+{
+	return write_relocate_add(sechdrs, strtab, symindex, relsec, me, true);
+}
+
+#ifdef CONFIG_LIVEPATCH
+void clear_relocate_add(Elf64_Shdr *sechdrs,
+			const char *strtab,
+			unsigned int symindex,
+			unsigned int relsec,
+			struct module *me)
+{
+	write_relocate_add(sechdrs, strtab, symindex, relsec, me, false);
+}
+#endif
+
 #endif
 
 int module_finalize(const Elf_Ehdr *hdr,