x86: Add support for 64-bit place relative relocations

Add support for R_X86_64_PC64 relocations, which operate on 64-bit
quantities holding a relative symbol reference. Also remove the
definition of R_X86_64_NUM: given that it is currently unused, it
is unclear what the new value should be.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-s390@vger.kernel.org
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Jessica Yu <jeyu@kernel.org>
Link: https://lkml.kernel.org/r/20180919065144.25010-5-ard.biesheuvel@linaro.org

arch/x86/include/asm/elf.h

@@ -62,8 +62,7 @@ typedef struct user_fxsr_struct elf_fpxregset_t;
 #define R_X86_64_PC16		13	/* 16 bit sign extended pc relative */
 #define R_X86_64_8		14	/* Direct 8 bit sign extended  */
 #define R_X86_64_PC8		15	/* 8 bit sign extended pc relative */
-
-#define R_X86_64_NUM		16
+#define R_X86_64_PC64		24	/* Place relative 64-bit signed */
 
 /*
  * These are used to set parameters in the core dumps.

arch/x86/kernel/module.c

@@ -201,6 +201,12 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
 				goto overflow;
 #endif
 			break;
+		case R_X86_64_PC64:
+			if (*(u64 *)loc != 0)
+				goto invalid_relocation;
+			val -= (u64)loc;
+			*(u64 *)loc = val;
+			break;
 		default:
 			pr_err("%s: Unknown rela relocation: %llu\n",
 			       me->name, ELF64_R_TYPE(rel[i].r_info));

arch/x86/tools/relocs.c

@@ -196,6 +196,7 @@ static const char *rel_type(unsigned type)
 #if ELF_BITS == 64
 		REL_TYPE(R_X86_64_NONE),
 		REL_TYPE(R_X86_64_64),
+		REL_TYPE(R_X86_64_PC64),
 		REL_TYPE(R_X86_64_PC32),
 		REL_TYPE(R_X86_64_GOT32),
 		REL_TYPE(R_X86_64_PLT32),
@@ -782,6 +783,15 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
 			add_reloc(&relocs32neg, offset);
 		break;
 
+	case R_X86_64_PC64:
+		/*
+		 * Only used by jump labels
+		 */
+		if (is_percpu_sym(sym, symname))
+			die("Invalid R_X86_64_PC64 relocation against per-CPU symbol %s\n",
+			    symname);
+		break;
+
 	case R_X86_64_32:
 	case R_X86_64_32S:
 	case R_X86_64_64:

arch/x86/um/asm/elf.h

@@ -116,8 +116,7 @@ do {								\
 #define R_X86_64_PC16		13	/* 16 bit sign extended pc relative */
 #define R_X86_64_8		14	/* Direct 8 bit sign extended  */
 #define R_X86_64_PC8		15	/* 8 bit sign extended pc relative */
-
-#define R_X86_64_NUM		16
+#define R_X86_64_PC64		24	/* Place relative 64-bit signed */
 
 /*
  * This is used to ensure we don't load something for the wrong architecture.