linux-kernel - [PATCH AUTOSEL 5.18 20/54] objtool: Update Retpoline validation

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Message-Id: <20220720011031.1023305-20-sashal@kernel.org>
Date:   Tue, 19 Jul 2022 21:09:57 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...e.de>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Sasha Levin <sashal@...nel.org>, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, luto@...nel.org, jgross@...e.com,
        pawan.kumar.gupta@...ux.intel.com, xen-devel@...ts.xenproject.org
Subject: [PATCH AUTOSEL 5.18 20/54] objtool: Update Retpoline validation

From: Peter Zijlstra <peterz@...radead.org>

[ Upstream commit 9bb2ec608a209018080ca262f771e6a9ff203b6f ]

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

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@...nel.org>
Signed-off-by: Borislav Petkov <bp@...e.de>
Signed-off-by: Sasha Levin <sashal@...nel.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(-)

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 92290b4f1c96..a790109f9337 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -75,6 +75,12 @@
 	.popsection
 .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
diff --git a/arch/x86/mm/mem_encrypt_boot.S b/arch/x86/mm/mem_encrypt_boot.S
index d94dea450fa6..9de3d900bc92 100644
--- 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:
diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index 3a2cd93bf059..fa884fc73e07 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -26,6 +26,7 @@ SYM_CODE_START(hypercall_page)
 	.rept (PAGE_SIZE / 32)
 		UNWIND_HINT_FUNC
 		ANNOTATE_NOENDBR
+		ANNOTATE_UNRET_SAFE
 		ret
 		/*
 		 * Xen will write the hypercall page, and sort out ENDBR.
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 204519704f3b..2daa0dce199b 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2097,8 +2097,9 @@ static int read_retpoline_hints(struct objtool_file *file)
 		}
 
 		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;
 		}
@@ -3631,7 +3632,8 @@ static int validate_retpoline(struct objtool_file *file)
 
 	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)
@@ -3646,9 +3648,14 @@ static int validate_retpoline(struct objtool_file *file)
 		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++;
 	}
-- 
2.35.1