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objtool: Handle Clang RSP musical chairs

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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: Arnd 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: Josh Poimboeuf <jpoimboe@kernel.org>
This commit is contained in:
Josh Poimboeuf
2026-03-06 09:35:06 -08:00
parent 1fd1dc4172
commit 7fdaa640c8
2 changed files with 40 additions and 42 deletions
Download Patch File Download Diff File Expand all files Collapse all files

68
tools/objtool/arch/x86/decode.c
View File

@@ -395,52 +395,36 @@ 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 */
ADD_OP(op) {
op->src.type = OP_SRC_REG;
op->src.reg = CFI_SP;
op->dest.type = OP_DEST_REG;
op->dest.reg = modrm_rm;
}
break;
} else {
/* skip RIP relative displacement */
if (is_RIP())
break;
/* skip nontrivial SIB */
if (have_SIB()) {
modrm_rm = sib_base;
if (sib_index != CFI_SP)
break;
}
/* mov %rsp, disp(%reg) */
ADD_OP(op) {
op->src.type = OP_SRC_REG;
op->src.reg = CFI_SP;
op->dest.type = OP_DEST_REG_INDIRECT;
op->dest.reg = modrm_rm;
op->dest.offset = ins.displacement.value;
}
break;
}
break;
}
if (rm_is_reg(CFI_SP)) {
/* mov reg, %rsp */
if (mod_is_reg()) {
/* mov reg, reg */
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;
op->dest.reg = modrm_rm;
}
break;
}
/* skip RIP relative displacement */
if (is_RIP())
break;
/* skip nontrivial SIB */
if (have_SIB()) {
modrm_rm = sib_base;
if (sib_index != CFI_SP)
break;
}
/* mov %rsp, disp(%reg) */
if (modrm_reg == CFI_SP) {
ADD_OP(op) {
op->src.type = OP_SRC_REG;
op->src.reg = CFI_SP;
op->dest.type = OP_DEST_REG_INDIRECT;
op->dest.reg = modrm_rm;
op->dest.offset = ins.displacement.value;
}
break;
}

14
tools/objtool/check.c
View File

@@ -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;