Commit d9e9d230 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Borislav Petkov
Browse files

x86,objtool: Create .return_sites 



Find all the return-thunk sites and record them in a .return_sites
section such that the kernel can undo this.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Reviewed-by: default avatarJosh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
parent 15e67227

tools/objtool/arch/x86/decode.c

+5 −0
Original line number Diff line number Diff line
@@ -787,3 +787,8 @@ bool arch_is_retpoline(struct symbol *sym) 
{

	return !strncmp(sym->name, "__x86_indirect_", 15);

}



bool arch_is_rethunk(struct symbol *sym)

{

	return !strcmp(sym->name, "__x86_return_thunk");

}

tools/objtool/check.c

+74 −0
Original line number Diff line number Diff line
@@ -749,6 +749,52 @@ static int create_retpoline_sites_sections(struct objtool_file *file) 
	return 0;

}



static int create_return_sites_sections(struct objtool_file *file)

{

	struct instruction *insn;

	struct section *sec;

	int idx;



	sec = find_section_by_name(file->elf, ".return_sites");

	if (sec) {

		WARN("file already has .return_sites, skipping");

		return 0;

	}



	idx = 0;

	list_for_each_entry(insn, &file->return_thunk_list, call_node)

		idx++;



	if (!idx)

		return 0;



	sec = elf_create_section(file->elf, ".return_sites", 0,

				 sizeof(int), idx);

	if (!sec) {

		WARN("elf_create_section: .return_sites");

		return -1;

	}



	idx = 0;

	list_for_each_entry(insn, &file->return_thunk_list, call_node) {



		int *site = (int *)sec->data->d_buf + idx;

		*site = 0;



		if (elf_add_reloc_to_insn(file->elf, sec,

					  idx * sizeof(int),

					  R_X86_64_PC32,

					  insn->sec, insn->offset)) {

			WARN("elf_add_reloc_to_insn: .return_sites");

			return -1;

		}



		idx++;

	}



	return 0;

}



static int create_ibt_endbr_seal_sections(struct objtool_file *file)

{

	struct instruction *insn;
@@ -1083,6 +1129,11 @@ __weak bool arch_is_retpoline(struct symbol *sym) 
	return false;

}



__weak bool arch_is_rethunk(struct symbol *sym)

{

	return false;

}



#define NEGATIVE_RELOC	((void *)-1L)



static struct reloc *insn_reloc(struct objtool_file *file, struct instruction *insn)
@@ -1250,6 +1301,18 @@ static void add_retpoline_call(struct objtool_file *file, struct instruction *in 
	annotate_call_site(file, insn, false);

}



static void add_return_call(struct objtool_file *file, struct instruction *insn)

{

	/*

	 * Return thunk tail calls are really just returns in disguise,

	 * so convert them accordingly.

	 */

	insn->type = INSN_RETURN;

	insn->retpoline_safe = true;



	list_add_tail(&insn->call_node, &file->return_thunk_list);

}



static bool same_function(struct instruction *insn1, struct instruction *insn2)

{

	return insn1->func->pfunc == insn2->func->pfunc;
@@ -1302,6 +1365,9 @@ static int add_jump_destinations(struct objtool_file *file) 
		} else if (reloc->sym->retpoline_thunk) {

			add_retpoline_call(file, insn);

			continue;

		} else if (reloc->sym->return_thunk) {

			add_return_call(file, insn);

			continue;

		} else if (insn->func) {

			/*

			 * External sibling call or internal sibling call with
@@ -2184,6 +2250,9 @@ static int classify_symbols(struct objtool_file *file) 
			if (arch_is_retpoline(func))

				func->retpoline_thunk = true;



			if (arch_is_rethunk(func))

				func->return_thunk = true;



			if (!strcmp(func->name, "__fentry__"))

				func->fentry = true;
@@ -3972,6 +4041,11 @@ int check(struct objtool_file *file) 
		if (ret < 0)

			goto out;

		warnings += ret;



		ret = create_return_sites_sections(file);

		if (ret < 0)

			goto out;

		warnings += ret;

	}



	if (opts.mcount) {

tools/objtool/include/objtool/arch.h

+1 −0
Original line number Diff line number Diff line
@@ -89,6 +89,7 @@ const char *arch_ret_insn(int len); 
int arch_decode_hint_reg(u8 sp_reg, int *base);



bool arch_is_retpoline(struct symbol *sym);

bool arch_is_rethunk(struct symbol *sym);



int arch_rewrite_retpolines(struct objtool_file *file);

tools/objtool/include/objtool/elf.h

+1 −0
Original line number Diff line number Diff line
@@ -57,6 +57,7 @@ struct symbol { 
	u8 uaccess_safe      : 1;

	u8 static_call_tramp : 1;

	u8 retpoline_thunk   : 1;

	u8 return_thunk      : 1;

	u8 fentry            : 1;

	u8 profiling_func    : 1;

	struct list_head pv_target;

tools/objtool/include/objtool/objtool.h

+1 −0
Original line number Diff line number Diff line
@@ -24,6 +24,7 @@ struct objtool_file { 
	struct list_head insn_list;

	DECLARE_HASHTABLE(insn_hash, 20);

	struct list_head retpoline_call_list;

	struct list_head return_thunk_list;

	struct list_head static_call_list;

	struct list_head mcount_loc_list;

	struct list_head endbr_list;