This is a note to let you know that I've just added the patch titled x86/retpoline: Use -mfunction-return to the 5.18-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: x86-retpoline-use-mfunction-return.patch and it can be found in the queue-5.18 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Tue Jul 12 05:03:58 PM CEST 2022 From: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Date: Tue, 14 Jun 2022 23:15:36 +0200 Subject: x86/retpoline: Use -mfunction-return From: Peter Zijlstra <peterz@xxxxxxxxxxxxx> commit 0b53c374b9eff2255a386f1f1cfb9a928e52a5ae upstream. Utilize -mfunction-return=thunk-extern when available to have the compiler replace RET instructions with direct JMPs to the symbol __x86_return_thunk. This does not affect assembler (.S) sources, only C sources. -mfunction-return=thunk-extern has been available since gcc 7.3 and clang 15. Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Reviewed-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Tested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/Makefile | 2 ++ arch/x86/include/asm/nospec-branch.h | 2 ++ arch/x86/lib/retpoline.S | 13 +++++++++++++ 3 files changed, 17 insertions(+) --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -15,11 +15,13 @@ endif ifdef CONFIG_CC_IS_GCC RETPOLINE_CFLAGS := $(call cc-option,-mindirect-branch=thunk-extern -mindirect-branch-register) RETPOLINE_CFLAGS += $(call cc-option,-mindirect-branch-cs-prefix) +RETPOLINE_CFLAGS += $(call cc-option,-mfunction-return=thunk-extern) RETPOLINE_VDSO_CFLAGS := $(call cc-option,-mindirect-branch=thunk-inline -mindirect-branch-register) endif ifdef CONFIG_CC_IS_CLANG RETPOLINE_CFLAGS := -mretpoline-external-thunk RETPOLINE_VDSO_CFLAGS := -mretpoline +RETPOLINE_CFLAGS += $(call cc-option,-mfunction-return=thunk-extern) endif export RETPOLINE_CFLAGS export RETPOLINE_VDSO_CFLAGS --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -123,6 +123,8 @@ typedef u8 retpoline_thunk_t[RETPOLINE_THUNK_SIZE]; extern retpoline_thunk_t __x86_indirect_thunk_array[]; +extern void __x86_return_thunk(void); + #ifdef CONFIG_RETPOLINE #define GEN(reg) \ --- a/arch/x86/lib/retpoline.S +++ b/arch/x86/lib/retpoline.S @@ -67,3 +67,16 @@ SYM_CODE_END(__x86_indirect_thunk_array) #define GEN(reg) EXPORT_THUNK(reg) #include <asm/GEN-for-each-reg.h> #undef GEN + +/* + * This function name is magical and is used by -mfunction-return=thunk-extern + * for the compiler to generate JMPs to it. + */ +SYM_CODE_START(__x86_return_thunk) + UNWIND_HINT_EMPTY + ANNOTATE_NOENDBR + ret + int3 +SYM_CODE_END(__x86_return_thunk) + +__EXPORT_THUNK(__x86_return_thunk) Patches currently in stable-queue which might be from peterz@xxxxxxxxxxxxx are queue-5.18/x86-sev-avoid-using-__x86_return_thunk.patch queue-5.18/kvm-vmx-prevent-rsb-underflow-before-vmenter.patch queue-5.18/x86-ftrace-use-alternative-ret-encoding.patch queue-5.18/objtool-re-add-unwind_hint_-save_restore.patch queue-5.18/x86-bugs-add-retbleed-ibpb.patch queue-5.18/x86-bugs-enable-stibp-for-jmp2ret.patch queue-5.18/x86-retpoline-cleanup-some-ifdefery.patch queue-5.18/kvm-vmx-flatten-__vmx_vcpu_run.patch queue-5.18/x86-kvm-vmx-make-noinstr-clean.patch queue-5.18/x86-retbleed-add-fine-grained-kconfig-knobs.patch queue-5.18/x86-cpu-amd-add-spectral-chicken.patch queue-5.18/kvm-vmx-fix-ibrs-handling-after-vmexit.patch queue-5.18/kvm-vmx-prevent-guest-rsb-poisoning-attacks-with-eibrs.patch queue-5.18/x86-vsyscall_emu-64-don-t-use-ret-in-vsyscall-emulation.patch queue-5.18/x86-add-magic-amd-return-thunk.patch queue-5.18/x86-bugs-keep-a-per-cpu-ia32_spec_ctrl-value.patch queue-5.18/x86-objtool-create-.return_sites.patch queue-5.18/x86-kvm-fix-setcc-emulation-for-return-thunks.patch queue-5.18/x86-retpoline-swizzle-retpoline-thunk.patch queue-5.18/x86-speculation-fix-firmware-entry-spec_ctrl-handling.patch queue-5.18/x86-speculation-add-spectre_v2-ibrs-option-to-support-kernel-ibrs.patch queue-5.18/x86-xen-add-untrain_ret.patch queue-5.18/x86-undo-return-thunk-damage.patch queue-5.18/x86-entry-avoid-very-early-ret.patch queue-5.18/x86-entry-move-push_and_clear_regs-back-into-error_entry.patch queue-5.18/x86-speculation-fill-rsb-on-vmexit-for-ibrs.patch queue-5.18/objtool-add-entry-unret-validation.patch queue-5.18/kvm-vmx-convert-launched-argument-to-flags.patch queue-5.18/x86-bpf-use-alternative-ret-encoding.patch queue-5.18/x86-common-stamp-out-the-stepping-madness.patch queue-5.18/x86-bugs-split-spectre_v2_select_mitigation-and-spectre_v2_user_select_mitigation.patch queue-5.18/x86-bugs-report-intel-retbleed-vulnerability.patch queue-5.18/x86-cpufeatures-move-retpoline-flags-to-word-11.patch queue-5.18/x86-speculation-fix-spec_ctrl-write-on-smt-state-change.patch queue-5.18/x86-retpoline-use-mfunction-return.patch queue-5.18/x86-xen-rename-sys-entry-points.patch queue-5.18/x86-bugs-optimize-spec_ctrl-msr-writes.patch queue-5.18/x86-bugs-report-amd-retbleed-vulnerability.patch queue-5.18/x86-static_call-use-alternative-ret-encoding.patch queue-5.18/x86-speculation-fix-rsb-filling-with-config_retpoline-n.patch queue-5.18/x86-use-return-thunk-in-asm-code.patch queue-5.18/intel_idle-disable-ibrs-during-long-idle.patch queue-5.18/x86-entry-remove-skip_r11rcx.patch queue-5.18/x86-speculation-use-cached-host-spec_ctrl-value-for-guest-entry-exit.patch queue-5.18/x86-bugs-add-amd-retbleed-boot-parameter.patch queue-5.18/x86-entry-add-kernel-ibrs-implementation.patch queue-5.18/objtool-treat-.text.__x86.-as-noinstr.patch queue-5.18/objtool-update-retpoline-validation.patch