[PATCH 5.18 148/231] objtool: Update Retpoline validation

Greg Kroah-Hartman
2022-07-19T13:05:54Z

From: Peter Zijlstra <peterz@infradead.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@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>
Signed-off-by: Sasha Levin <sashal@kernel.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 da251a5645b0..f1a7ecd0a7c7 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 13af6fe453e3..ffaa62167f6e 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 f66e4ac0af94..fbe41203fc9b 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2030,8 +2030,9 @@ 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;
}
@@ -3561,7 +3562,8 @@ 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)
@@ -3576,9 +3578,14 @@ 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