Re: [PATCH 5.18 34/61] objtool: Update Retpoline validation

Jiri Slaby
2022-07-13T07:45:33Z

On 12. 07. 22, 20:39, Greg Kroah-Hartman wrote:
> 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.

Hi,

this breaks compilation on i386:
> arch/x86/kernel/../../x86/xen/xen-head.S:35: Error: no such
instruction: `annotate_unret_safe'

Config:
https://raw.githubusercontent.com/openSUSE/kernel-source/stable/config/i386/pae

And yeah, upstream¹⁾ is affected too.

¹⁾I am at commit b047602d579b4fb028128a525f056bbdc890e7f0.

> 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: 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
> @@ -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.
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -2114,8 +2114,9 @@ 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;
> }
> @@ -3648,7 +3649,8 @@ 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)
> @@ -3663,9 +3665,14 @@ 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++;
> }
>
>

--
js
suse labs