Commit 7fdaa640 authored by Josh Poimboeuf's avatar Josh Poimboeuf
Browse files

objtool: Handle Clang RSP musical chairs 



For no apparent reason (possibly related to CONFIG_KMSAN), Clang can
randomly pass the value of RSP to other registers and then back again to
RSP.  Handle that accordingly.

Fixes the following warnings:

  drivers/input/misc/uinput.o: warning: objtool: uinput_str_to_user+0x165: undefined stack state
  drivers/input/misc/uinput.o: warning: objtool: uinput_str_to_user+0x165: unknown CFA base reg -1

Reported-by: default avatarArnd Bergmann <arnd@arndb.de>
Closes: https://lore.kernel.org/90956545-2066-46e3-b547-10c884582eb0@app.fastmail.com
Link: https://patch.msgid.link/240e6a172cc73292499334a3724d02ccb3247fc7.1772818491.git.jpoimboe@kernel.org


Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@kernel.org>
parent 1fd1dc41

tools/objtool/arch/x86/decode.c

+23 −39
Original line number Diff line number Diff line
@@ -395,19 +395,17 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec 
		if (!rex_w)

			break;



		if (modrm_reg == CFI_SP) {



		if (mod_is_reg()) {

				/* mov %rsp, reg */

			/* mov reg, reg */

			ADD_OP(op) {

				op->src.type = OP_SRC_REG;

					op->src.reg = CFI_SP;

				op->src.reg = modrm_reg;

				op->dest.type = OP_DEST_REG;

				op->dest.reg = modrm_rm;

			}

			break;

		}



			} else {

		/* skip RIP relative displacement */

		if (is_RIP())

			break;
@@ -420,6 +418,7 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec 
		}



		/* mov %rsp, disp(%reg) */

		if (modrm_reg == CFI_SP) {

			ADD_OP(op) {

				op->src.type = OP_SRC_REG;

				op->src.reg = CFI_SP;
@@ -430,21 +429,6 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec 
			break;

		}



			break;

		}



		if (rm_is_reg(CFI_SP)) {



			/* mov reg, %rsp */

			ADD_OP(op) {

				op->src.type = OP_SRC_REG;

				op->src.reg = modrm_reg;

				op->dest.type = OP_DEST_REG;

				op->dest.reg = CFI_SP;

			}

			break;

		}



		fallthrough;

	case 0x88:

		if (!rex_w)

tools/objtool/check.c

+14 −0
Original line number Diff line number Diff line
@@ -3000,6 +3000,20 @@ static int update_cfi_state(struct instruction *insn, 
				cfi->stack_size += 8;

			}



			else if (cfi->vals[op->src.reg].base == CFI_CFA) {

				/*

				 * Clang RSP musical chairs:

				 *

				 *   mov %rsp, %rdx [handled above]

				 *   ...

				 *   mov %rdx, %rbx [handled here]

				 *   ...

				 *   mov %rbx, %rsp [handled above]

				 */

				cfi->vals[op->dest.reg].base = CFI_CFA;

				cfi->vals[op->dest.reg].offset = cfi->vals[op->src.reg].offset;

			}





			break;