linux-hardening - [RFC PATCH 10/17] objtool: arm64: Accept padding in code sections

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Message-Id: <20210120173800.1660730-11-jthierry@redhat.com>
Date:   Wed, 20 Jan 2021 18:37:53 +0100
From:   Julien Thierry <jthierry@...hat.com>
To:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc:     catalin.marinas@....com, will@...nel.org, ardb@...nel.org,
        masahiroy@...nel.org, keescook@...omium.org,
        michal.lkml@...kovi.net, jpoimboe@...hat.com, peterz@...radead.org,
        mark.rutland@....com, broonie@...nel.org,
        linux-efi@...r.kernel.org, linux-hardening@...r.kernel.org,
        Julien Thierry <jthierry@...hat.com>
Subject: [RFC PATCH 10/17] objtool: arm64: Accept padding in code sections

The compiler can introduce some '0' words in code sections to pad the
end of functions.
Similar to load literal functions, record these zero words to remove
the "struct instruction" created for them.

Signed-off-by: Julien Thierry <jthierry@...hat.com>
---
 tools/objtool/arch/arm64/decode.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/tools/objtool/arch/arm64/decode.c b/tools/objtool/arch/arm64/decode.c
index b4d4d5b051b0..ed5ef0b52bbe 100644
--- a/tools/objtool/arch/arm64/decode.c
+++ b/tools/objtool/arch/arm64/decode.c
@@ -362,8 +362,23 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
 
 	switch (aarch64_get_insn_class(insn)) {
 	case AARCH64_INSN_CLS_UNKNOWN:
-		WARN("can't decode instruction at %s:0x%lx", sec->name, offset);
-		return -1;
+	{
+		/*
+		 * There are a few reasons we might have non-valid opcodes in
+		 * code sections:
+		 * - For load literal, assembler can generate the data to be
+		 *   loaded in the code section
+		 * - Compiler/assembler can generate zeroes to pad function that
+		 *   do not end on 8-byte alignment
+		 */
+		/* Compiler might put zeroes as padding */
+		if (record_invalid_insn(sec, offset, insn == 0x0))
+			return -1;
+
+		*type = INSN_OTHER;
+
+		break;
+	}
 	case AARCH64_INSN_CLS_DP_IMM:
 		/* Mov register to and from SP are aliases of add_imm */
 		if (aarch64_insn_is_add_imm(insn) ||
-- 
2.25.4