From: Vasily Gorbik Date: Sun, 6 Mar 2022 19:56:07 +0000 (+0100) Subject: s390/nospec: add an option to use thunk-extern X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=1d2ad084800edad81cdc955304272742b10721c7;p=linux.git s390/nospec: add an option to use thunk-extern Currently with -mindirect-branch=thunk and -mfunction-return=thunk compiler options expoline thunks are put into individual COMDAT group sections. s390 is the only architecture which has group sections and it has implications for kpatch and objtool tools support. Using -mindirect-branch=thunk-extern and -mfunction-return=thunk-extern is an alternative, which comes with a need to generate all required expoline thunks manually. Unfortunately modules area is too far away from the kernel image, and expolines from the kernel image cannon be used. But since all new distributions (except Debian) build kernels for machine generations newer than z10, where "exrl" instruction is available, that leaves only 16 expolines thunks possible. Provide an option to build the kernel with -mindirect-branch=thunk-extern and -mfunction-return=thunk-extern for z10 or newer. This also requires to postlink expoline thunks into all modules explicitly. Currently modules already contain most expolines anyhow. Unfortunately -mindirect-branch=thunk-extern and -mfunction-return=thunk-extern options support is broken in gcc <= 11.2. Additional compile test is required to verify proper gcc support. Acked-by: Ilya Leoshkevich Co-developed-by: Sumanth Korikkar Signed-off-by: Sumanth Korikkar Signed-off-by: Vasily Gorbik --- diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig index a492376d6e3f0..115b8cddefeee 100644 --- a/arch/s390/Kconfig +++ b/arch/s390/Kconfig @@ -585,6 +585,7 @@ config KERNEL_NOBP config EXPOLINE def_bool n + depends on $(cc-option,-mindirect-branch=thunk) prompt "Avoid speculative indirect branches in the kernel" help Compile the kernel with the expoline compiler options to guard @@ -595,6 +596,20 @@ config EXPOLINE If unsure, say N. +config EXPOLINE_EXTERN + def_bool n + depends on EXPOLINE + depends on HAVE_MARCH_Z10_FEATURES + depends on CC_IS_GCC && GCC_VERSION >= 110200 + depends on $(success,$(srctree)/arch/s390/tools/gcc-thunk-extern.sh $(CC)) + prompt "Generate expolines as extern functions." + help + This option is required for some tooling like kpatch. The kernel is + compiled with -mindirect-branch=thunk-extern and requires a newer + compiler. + + If unsure, say N. + choice prompt "Expoline default" depends on EXPOLINE diff --git a/arch/s390/Makefile b/arch/s390/Makefile index 2edf25b44c4b3..bd75128b7d798 100644 --- a/arch/s390/Makefile +++ b/arch/s390/Makefile @@ -81,14 +81,18 @@ ifneq ($(call cc-option,-mstack-size=8192 -mstack-guard=128),) endif ifdef CONFIG_EXPOLINE - ifneq ($(call cc-option,$(CC_FLAGS_MARCH) -mindirect-branch=thunk),) + ifdef CONFIG_EXPOLINE_EXTERN + KBUILD_LDFLAGS_MODULE += arch/s390/lib/expoline.o + CC_FLAGS_EXPOLINE := -mindirect-branch=thunk-extern + CC_FLAGS_EXPOLINE += -mfunction-return=thunk-extern + else CC_FLAGS_EXPOLINE := -mindirect-branch=thunk CC_FLAGS_EXPOLINE += -mfunction-return=thunk - CC_FLAGS_EXPOLINE += -mindirect-branch-table - export CC_FLAGS_EXPOLINE - cflags-y += $(CC_FLAGS_EXPOLINE) -DCC_USING_EXPOLINE - aflags-y += -DCC_USING_EXPOLINE endif + CC_FLAGS_EXPOLINE += -mindirect-branch-table + export CC_FLAGS_EXPOLINE + cflags-y += $(CC_FLAGS_EXPOLINE) -DCC_USING_EXPOLINE + aflags-y += -DCC_USING_EXPOLINE endif ifdef CONFIG_FUNCTION_TRACER diff --git a/arch/s390/include/asm/nospec-insn.h b/arch/s390/include/asm/nospec-insn.h index 4397eae15e342..bbb5c4d84db93 100644 --- a/arch/s390/include/asm/nospec-insn.h +++ b/arch/s390/include/asm/nospec-insn.h @@ -18,7 +18,11 @@ _LC_BR_R1 = __LC_BR_R1 * the various thunks are merged into a single copy. */ .macro __THUNK_PROLOG_NAME name +#ifdef CONFIG_EXPOLINE_EXTERN + .pushsection .text,"ax",@progbits +#else .pushsection .text.\name,"axG",@progbits,\name,comdat +#endif .globl \name .hidden \name .type \name,@function @@ -115,7 +119,13 @@ _LC_BR_R1 = __LC_BR_R1 555: br \reg .endm +#ifdef CONFIG_EXPOLINE_EXTERN + .macro GEN_BR_THUNK reg,ruse=%r1 + .endm + .macro GEN_BR_THUNK_EXTERN reg,ruse=%r1 +#else .macro GEN_BR_THUNK reg,ruse=%r1 +#endif __DECODE_RR __THUNK_PROLOG_BR,\reg,\ruse __THUNK_EX_BR \reg,\ruse __THUNK_EPILOG diff --git a/arch/s390/lib/Makefile b/arch/s390/lib/Makefile index 69feb8ed3312d..5d415b3db6d14 100644 --- a/arch/s390/lib/Makefile +++ b/arch/s390/lib/Makefile @@ -7,6 +7,7 @@ lib-y += delay.o string.o uaccess.o find.o spinlock.o obj-y += mem.o xor.o lib-$(CONFIG_KPROBES) += probes.o lib-$(CONFIG_UPROBES) += probes.o +obj-$(CONFIG_EXPOLINE_EXTERN) += expoline.o obj-$(CONFIG_S390_KPROBES_SANITY_TEST) += test_kprobes_s390.o test_kprobes_s390-objs += test_kprobes_asm.o test_kprobes.o diff --git a/arch/s390/lib/expoline.S b/arch/s390/lib/expoline.S new file mode 100644 index 0000000000000..92ed8409a7a44 --- /dev/null +++ b/arch/s390/lib/expoline.S @@ -0,0 +1,12 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#include +#include + +.macro GEN_ALL_BR_THUNK_EXTERN + .irp r1,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15 + GEN_BR_THUNK_EXTERN %r\r1 + .endr +.endm + +GEN_ALL_BR_THUNK_EXTERN diff --git a/arch/s390/tools/gcc-thunk-extern.sh b/arch/s390/tools/gcc-thunk-extern.sh new file mode 100755 index 0000000000000..20bcbf6dd7abf --- /dev/null +++ b/arch/s390/tools/gcc-thunk-extern.sh @@ -0,0 +1,24 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0 +# Borrowed from gcc: gcc/testsuite/gcc.target/s390/nobp-section-type-conflict.c +# Checks that we don't get error: section type conflict with ‘put_page’. + +cat << "END" | $@ -x c - -fno-PIE -march=z10 -mindirect-branch=thunk-extern -mfunction-return=thunk-extern -mindirect-branch-table -O2 -c -o /dev/null +int a; +int b (void); +void c (int); + +static void +put_page (void) +{ + if (b ()) + c (a); +} + +__attribute__ ((__section__ (".init.text"), __cold__)) void +d (void) +{ + put_page (); + put_page (); +} +END diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c index 6bfa332179140..dbc0aaf69e434 100644 --- a/scripts/mod/modpost.c +++ b/scripts/mod/modpost.c @@ -658,6 +658,11 @@ static int ignore_undef_symbol(struct elf_info *info, const char *symname) strstarts(symname, "_savevr_") || strcmp(symname, ".TOC.") == 0) return 1; + + if (info->hdr->e_machine == EM_S390) + /* Expoline thunks are linked on all kernel modules during final link of .ko */ + if (strstarts(symname, "__s390_indirect_jump_r")) + return 1; /* Do not ignore this symbol */ return 0; }