[PATCH RFC 33/43] objtool: Add validation for x86 PIE support

[Hou Wenlong]

For x86 PIE binary, only RIP-relative addressing is allowed, however,
there are still a little absolute references of R_X86_64_64 relocation
type for data section and a little absolute references of R_X86_64_32S
relocation type in pvh_start_xen() function.

Suggested-by: Lai Jiangshan <jiangshan.ljs@xxxxxxxxxxxx>
Signed-off-by: Hou Wenlong <houwenlong.hwl@xxxxxxxxxxxx>
Cc: Thomas Garnier <thgarnie@xxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
---
 arch/x86/Kconfig                        |  1 +
 scripts/Makefile.lib                    |  1 +
 tools/objtool/builtin-check.c           |  4 +-
 tools/objtool/check.c                   | 82 +++++++++++++++++++++++++
 tools/objtool/include/objtool/builtin.h |  1 +
 5 files changed, 88 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 715f0734d065..b753a54e5ea7 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2224,6 +2224,7 @@ config RELOCATABLE
 config X86_PIE
 	def_bool n
 	depends on X86_64
+	select OBJTOOL if HAVE_OBJTOOL
 
 config RANDOMIZE_BASE
 	bool "Randomize the address of the kernel image (KASLR)"
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 100a386fcd71..e3c804fbc421 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -270,6 +270,7 @@ objtool-args-$(CONFIG_HAVE_STATIC_CALL_INLINE)		+= --static-call
 objtool-args-$(CONFIG_HAVE_UACCESS_VALIDATION)		+= --uaccess
 objtool-args-$(CONFIG_GCOV_KERNEL)			+= --no-unreachable
 objtool-args-$(CONFIG_PREFIX_SYMBOLS)			+= --prefix=$(CONFIG_FUNCTION_PADDING_BYTES)
+objtool-args-$(CONFIG_X86_PIE)			        += --pie
 
 objtool-args = $(objtool-args-y)					\
 	$(if $(delay-objtool), --link)					\
diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index 7c175198d09f..1cf1d00464e0 100644
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -81,6 +81,7 @@ static const struct option check_options[] = {
 	OPT_BOOLEAN('t', "static-call", &opts.static_call, "annotate static calls"),
 	OPT_BOOLEAN('u', "uaccess", &opts.uaccess, "validate uaccess rules for SMAP"),
 	OPT_BOOLEAN(0  , "cfi", &opts.cfi, "annotate kernel control flow integrity (kCFI) function preambles"),
+	OPT_BOOLEAN(0, "pie", &opts.pie, "validate addressing rules for PIE"),
 	OPT_CALLBACK_OPTARG(0, "dump", NULL, NULL, "orc", "dump metadata", parse_dump),
 
 	OPT_GROUP("Options:"),
@@ -137,7 +138,8 @@ static bool opts_valid(void)
 	    opts.sls			||
 	    opts.stackval		||
 	    opts.static_call		||
-	    opts.uaccess) {
+	    opts.uaccess		||
+	    opts.pie) {
 		if (opts.dump_orc) {
 			ERROR("--dump can't be combined with other options");
 			return false;
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 5b600bbf2389..d67b80251eec 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -131,6 +131,27 @@ static struct instruction *prev_insn_same_sym(struct objtool_file *file,
 	for (insn = next_insn_same_sec(file, insn); insn;		\
 	     insn = next_insn_same_sec(file, insn))
 
+static struct instruction *find_insn_containing(struct objtool_file *file,
+						struct section *sec,
+						unsigned long offset)
+{
+	struct instruction *insn;
+
+	insn = find_insn(file, sec, 0);
+	if (!insn)
+		return NULL;
+
+	sec_for_each_insn_from(file, insn) {
+		if (insn->offset > offset)
+			return NULL;
+		if (insn->offset <= offset && (insn->offset + insn->len) > offset)
+			return insn;
+	}
+
+	return NULL;
+}
+
+
 static inline struct symbol *insn_call_dest(struct instruction *insn)
 {
 	if (insn->type == INSN_JUMP_DYNAMIC ||
@@ -4529,6 +4550,61 @@ static int validate_reachable_instructions(struct objtool_file *file)
 	return 0;
 }
 
+static int is_in_pvh_code(struct instruction *insn)
+{
+	struct symbol *sym = insn->sym;
+
+	return sym && !strcmp(sym->name, "pvh_start_xen");
+}
+
+static int validate_pie(struct objtool_file *file)
+{
+	struct section *sec;
+	struct reloc *reloc;
+	struct instruction *insn;
+	int warnings = 0;
+
+	for_each_sec(file, sec) {
+		if (!sec->reloc)
+			continue;
+		if (!(sec->sh.sh_flags & SHF_ALLOC))
+			continue;
+
+		list_for_each_entry(reloc, &sec->reloc->reloc_list, list) {
+			switch (reloc->type) {
+			case R_X86_64_NONE:
+			case R_X86_64_PC32:
+			case R_X86_64_PLT32:
+			case R_X86_64_64:
+			case R_X86_64_PC64:
+			case R_X86_64_GOTPCREL:
+				break;
+			case R_X86_64_32:
+			case R_X86_64_32S:
+				insn = find_insn_containing(file, sec, reloc->offset);
+				if (!insn) {
+					WARN("can't find relocate insn near %s+0x%lx",
+					     sec->name, reloc->offset);
+				} else {
+					if (is_in_pvh_code(insn))
+						break;
+					WARN("insn at %s+0x%lx is not compatible with PIE",
+					     sec->name, insn->offset);
+				}
+				warnings++;
+				break;
+			default:
+				WARN("unexpected relocation type %d at %s+0x%lx",
+				     reloc->type, sec->name, reloc->offset);
+				warnings++;
+				break;
+			}
+		}
+	}
+
+	return warnings;
+}
+
 int check(struct objtool_file *file)
 {
 	int ret, warnings = 0;
@@ -4673,6 +4749,12 @@ int check(struct objtool_file *file)
 		warnings += ret;
 	}
 
+	if (opts.pie) {
+		ret = validate_pie(file);
+		if (ret < 0)
+			return ret;
+		warnings += ret;
+	}
 
 	if (opts.stats) {
 		printf("nr_insns_visited: %ld\n", nr_insns_visited);
diff --git a/tools/objtool/include/objtool/builtin.h b/tools/objtool/include/objtool/builtin.h
index 2a108e648b7a..1151211a5cea 100644
--- a/tools/objtool/include/objtool/builtin.h
+++ b/tools/objtool/include/objtool/builtin.h
@@ -26,6 +26,7 @@ struct opts {
 	bool uaccess;
 	int prefix;
 	bool cfi;
+	bool pie;
 
 	/* options: */
 	bool backtrace;
-- 
2.31.1