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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Borislav Petkov <bp@suse.de>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Subject: [PATCH 5.15 52/78] objtool: Update Retpoline validation
Date:   Tue, 12 Jul 2022 20:39:22 +0200
Message-Id: <20220712183240.986838708@linuxfoundation.org>
In-Reply-To: <20220712183238.844813653@linuxfoundation.org>
References: <20220712183238.844813653@linuxfoundation.org>
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From: Peter Zijlstra <peterz@infradead.org>

commit 9bb2ec608a209018080ca262f771e6a9ff203b6f upstream.

Update retpoline validation with the new CONFIG_RETPOLINE requirement of
not having bare naked RET instructions.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
[cascardo: conflict fixup at arch/x86/xen/xen-head.S]
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/x86/include/asm/nospec-branch.h |    6 ++++++
 arch/x86/mm/mem_encrypt_boot.S       |    2 ++
 arch/x86/xen/xen-head.S              |    1 +
 tools/objtool/check.c                |   19 +++++++++++++------
 4 files changed, 22 insertions(+), 6 deletions(-)

--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -76,6 +76,12 @@
 .endm
 
 /*
+ * (ab)use RETPOLINE_SAFE on RET to annotate away 'bare' RET instructions
+ * vs RETBleed validation.
+ */
+#define ANNOTATE_UNRET_SAFE ANNOTATE_RETPOLINE_SAFE
+
+/*
  * JMP_NOSPEC and CALL_NOSPEC macros can be used instead of a simple
  * indirect jmp/call which may be susceptible to the Spectre variant 2
  * attack.
--- a/arch/x86/mm/mem_encrypt_boot.S
+++ b/arch/x86/mm/mem_encrypt_boot.S
@@ -66,6 +66,7 @@ SYM_FUNC_START(sme_encrypt_execute)
 	pop	%rbp
 
 	/* Offset to __x86_return_thunk would be wrong here */
+	ANNOTATE_UNRET_SAFE
 	ret
 	int3
 SYM_FUNC_END(sme_encrypt_execute)
@@ -154,6 +155,7 @@ SYM_FUNC_START(__enc_copy)
 	pop	%r15
 
 	/* Offset to __x86_return_thunk would be wrong here */
+	ANNOTATE_UNRET_SAFE
 	ret
 	int3
 .L__enc_copy_end:
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -70,6 +70,7 @@ SYM_CODE_START(hypercall_page)
 	.rept (PAGE_SIZE / 32)
 		UNWIND_HINT_FUNC
 		.skip 31, 0x90
+		ANNOTATE_UNRET_SAFE
 		RET
 	.endr
 
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1894,8 +1894,9 @@ static int read_retpoline_hints(struct o
 		}
 
 		if (insn->type != INSN_JUMP_DYNAMIC &&
-		    insn->type != INSN_CALL_DYNAMIC) {
-			WARN_FUNC("retpoline_safe hint not an indirect jump/call",
+		    insn->type != INSN_CALL_DYNAMIC &&
+		    insn->type != INSN_RETURN) {
+			WARN_FUNC("retpoline_safe hint not an indirect jump/call/ret",
 				  insn->sec, insn->offset);
 			return -1;
 		}
@@ -3229,7 +3230,8 @@ static int validate_retpoline(struct obj
 
 	for_each_insn(file, insn) {
 		if (insn->type != INSN_JUMP_DYNAMIC &&
-		    insn->type != INSN_CALL_DYNAMIC)
+		    insn->type != INSN_CALL_DYNAMIC &&
+		    insn->type != INSN_RETURN)
 			continue;
 
 		if (insn->retpoline_safe)
@@ -3244,9 +3246,14 @@ static int validate_retpoline(struct obj
 		if (!strcmp(insn->sec->name, ".init.text") && !module)
 			continue;
 
-		WARN_FUNC("indirect %s found in RETPOLINE build",
-			  insn->sec, insn->offset,
-			  insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
+		if (insn->type == INSN_RETURN) {
+			WARN_FUNC("'naked' return found in RETPOLINE build",
+				  insn->sec, insn->offset);
+		} else {
+			WARN_FUNC("indirect %s found in RETPOLINE build",
+				  insn->sec, insn->offset,
+				  insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
+		}
 
 		warnings++;
 	}