[tip: objtool/core] objtool: Fully validate the stack frame

["tip-bot2 for Julien Thierry" <tip-bot2@xxxxxxxxxxxxx>]

The following commit has been merged into the objtool/core branch of tip:

Commit-ID:     fb084fde0c8106bc86df243411751c3421c07c08
Gitweb:        https://git.kernel.org/tip/fb084fde0c8106bc86df243411751c3421c07c08
Author:        Julien Thierry <jthierry@xxxxxxxxxx>
AuthorDate:    Wed, 14 Oct 2020 08:38:00 +01:00
Committer:     Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
CommitterDate: Wed, 13 Jan 2021 18:13:09 -06:00

objtool: Fully validate the stack frame

A valid stack frame should contain both the return address and the
previous frame pointer value.

On x86, the return value is placed on the stack by the calling
instructions. On other architectures, the callee needs to explicitly
save the return address on the stack.

Add the necessary checks to verify a function properly sets up all the
elements of the stack frame.

Signed-off-by: Julien Thierry <jthierry@xxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 tools/objtool/check.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 5f8d3ee..88210b0 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1733,12 +1733,20 @@ static bool has_modified_stack_frame(struct instruction *insn, struct insn_state
 	return false;
 }
 
+static bool check_reg_frame_pos(const struct cfi_reg *reg,
+				int expected_offset)
+{
+	return reg->base == CFI_CFA &&
+	       reg->offset == expected_offset;
+}
+
 static bool has_valid_stack_frame(struct insn_state *state)
 {
 	struct cfi_state *cfi = &state->cfi;
 
-	if (cfi->cfa.base == CFI_BP && cfi->regs[CFI_BP].base == CFI_CFA &&
-	    cfi->regs[CFI_BP].offset == -16)
+	if (cfi->cfa.base == CFI_BP &&
+	    check_reg_frame_pos(&cfi->regs[CFI_BP], -cfi->cfa.offset) &&
+	    check_reg_frame_pos(&cfi->regs[CFI_RA], -cfi->cfa.offset + 8))
 		return true;
 
 	if (cfi->drap && cfi->regs[CFI_BP].base == CFI_BP)
@@ -1867,8 +1875,7 @@ static int update_cfi_state(struct instruction *insn, struct cfi_state *cfi,
 		case OP_SRC_REG:
 			if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
 			    cfa->base == CFI_SP &&
-			    regs[CFI_BP].base == CFI_CFA &&
-			    regs[CFI_BP].offset == -cfa->offset) {
+			    check_reg_frame_pos(&regs[CFI_BP], -cfa->offset)) {
 
 				/* mov %rsp, %rbp */
 				cfa->base = op->dest.reg;