From: Peter Zijlstra peterz@infradead.org
commit f43b9876e857c739d407bc56df288b0ebe1a9164 upstream.
Do fine-grained Kconfig for all the various retbleed parts.
NOTE: if your compiler doesn't support return thunks this will silently 'upgrade' your mitigation to IBPB, you might not like this.
Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Borislav Petkov bp@suse.de [cascardo: there is no CONFIG_OBJTOOL] [cascardo: objtool calling and option parsing has changed] Signed-off-by: Thadeu Lima de Souza Cascardo cascardo@canonical.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- Makefile | 8 +- arch/x86/Kconfig | 106 +++++++++++++++++++++++-------- arch/x86/entry/calling.h | 4 + arch/x86/include/asm/disabled-features.h | 18 ++++- arch/x86/include/asm/linkage.h | 4 - arch/x86/include/asm/nospec-branch.h | 10 ++ arch/x86/include/asm/static_call.h | 2 arch/x86/kernel/alternative.c | 5 + arch/x86/kernel/cpu/amd.c | 2 arch/x86/kernel/cpu/bugs.c | 42 +++++++----- arch/x86/kernel/static_call.c | 2 arch/x86/kvm/emulate.c | 4 - arch/x86/lib/retpoline.S | 4 + scripts/Makefile.build | 1 scripts/link-vmlinux.sh | 2 security/Kconfig | 11 --- tools/objtool/builtin-check.c | 3 tools/objtool/check.c | 9 ++ tools/objtool/include/objtool/builtin.h | 2 19 files changed, 170 insertions(+), 69 deletions(-)
--- a/Makefile +++ b/Makefile @@ -687,14 +687,18 @@ endif
ifdef CONFIG_CC_IS_GCC RETPOLINE_CFLAGS := $(call cc-option,-mindirect-branch=thunk-extern -mindirect-branch-register) -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 + +ifdef CONFIG_RETHUNK +RETHUNK_CFLAGS := -mfunction-return=thunk-extern +RETPOLINE_CFLAGS += $(RETHUNK_CFLAGS) +endif + export RETPOLINE_CFLAGS export RETPOLINE_VDSO_CFLAGS
--- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -459,30 +459,6 @@ config GOLDFISH def_bool y depends on X86_GOLDFISH
-config RETPOLINE - bool "Avoid speculative indirect branches in kernel" - default y - help - Compile kernel with the retpoline compiler options to guard against - kernel-to-user data leaks by avoiding speculative indirect - branches. Requires a compiler with -mindirect-branch=thunk-extern - support for full protection. The kernel may run slower. - -config CC_HAS_SLS - def_bool $(cc-option,-mharden-sls=all) - -config CC_HAS_RETURN_THUNK - def_bool $(cc-option,-mfunction-return=thunk-extern) - -config SLS - bool "Mitigate Straight-Line-Speculation" - depends on CC_HAS_SLS && X86_64 - default n - help - Compile the kernel with straight-line-speculation options to guard - against straight line speculation. The kernel image might be slightly - larger. - config X86_CPU_RESCTRL bool "x86 CPU resource control support" depends on X86 && (CPU_SUP_INTEL || CPU_SUP_AMD) @@ -2410,6 +2386,88 @@ source "kernel/livepatch/Kconfig"
endmenu
+config CC_HAS_SLS + def_bool $(cc-option,-mharden-sls=all) + +config CC_HAS_RETURN_THUNK + def_bool $(cc-option,-mfunction-return=thunk-extern) + +menuconfig SPECULATION_MITIGATIONS + bool "Mitigations for speculative execution vulnerabilities" + default y + help + Say Y here to enable options which enable mitigations for + speculative execution hardware vulnerabilities. + + If you say N, all mitigations will be disabled. You really + should know what you are doing to say so. + +if SPECULATION_MITIGATIONS + +config PAGE_TABLE_ISOLATION + bool "Remove the kernel mapping in user mode" + default y + depends on (X86_64 || X86_PAE) + help + This feature reduces the number of hardware side channels by + ensuring that the majority of kernel addresses are not mapped + into userspace. + + See Documentation/x86/pti.rst for more details. + +config RETPOLINE + bool "Avoid speculative indirect branches in kernel" + default y + help + Compile kernel with the retpoline compiler options to guard against + kernel-to-user data leaks by avoiding speculative indirect + branches. Requires a compiler with -mindirect-branch=thunk-extern + support for full protection. The kernel may run slower. + +config RETHUNK + bool "Enable return-thunks" + depends on RETPOLINE && CC_HAS_RETURN_THUNK + default y + help + Compile the kernel with the return-thunks compiler option to guard + against kernel-to-user data leaks by avoiding return speculation. + Requires a compiler with -mfunction-return=thunk-extern + support for full protection. The kernel may run slower. + +config CPU_UNRET_ENTRY + bool "Enable UNRET on kernel entry" + depends on CPU_SUP_AMD && RETHUNK + default y + help + Compile the kernel with support for the retbleed=unret mitigation. + +config CPU_IBPB_ENTRY + bool "Enable IBPB on kernel entry" + depends on CPU_SUP_AMD + default y + help + Compile the kernel with support for the retbleed=ibpb mitigation. + +config CPU_IBRS_ENTRY + bool "Enable IBRS on kernel entry" + depends on CPU_SUP_INTEL + default y + help + Compile the kernel with support for the spectre_v2=ibrs mitigation. + This mitigates both spectre_v2 and retbleed at great cost to + performance. + +config SLS + bool "Mitigate Straight-Line-Speculation" + depends on CC_HAS_SLS && X86_64 + default n + help + Compile the kernel with straight-line-speculation options to guard + against straight line speculation. The kernel image might be slightly + larger. + +endif + config ARCH_HAS_ADD_PAGES def_bool y depends on X86_64 && ARCH_ENABLE_MEMORY_HOTPLUG --- a/arch/x86/entry/calling.h +++ b/arch/x86/entry/calling.h @@ -296,6 +296,7 @@ For 32-bit we have the following convent * Assumes x86_spec_ctrl_{base,current} to have SPEC_CTRL_IBRS set. */ .macro IBRS_ENTER save_reg +#ifdef CONFIG_CPU_IBRS_ENTRY ALTERNATIVE "jmp .Lend_@", "", X86_FEATURE_KERNEL_IBRS movl $MSR_IA32_SPEC_CTRL, %ecx
@@ -316,6 +317,7 @@ For 32-bit we have the following convent shr $32, %rdx wrmsr .Lend_@: +#endif .endm
/* @@ -323,6 +325,7 @@ For 32-bit we have the following convent * regs. Must be called after the last RET. */ .macro IBRS_EXIT save_reg +#ifdef CONFIG_CPU_IBRS_ENTRY ALTERNATIVE "jmp .Lend_@", "", X86_FEATURE_KERNEL_IBRS movl $MSR_IA32_SPEC_CTRL, %ecx
@@ -337,6 +340,7 @@ For 32-bit we have the following convent shr $32, %rdx wrmsr .Lend_@: +#endif .endm
/* --- a/arch/x86/include/asm/disabled-features.h +++ b/arch/x86/include/asm/disabled-features.h @@ -60,9 +60,19 @@ # define DISABLE_RETPOLINE 0 #else # define DISABLE_RETPOLINE ((1 << (X86_FEATURE_RETPOLINE & 31)) | \ - (1 << (X86_FEATURE_RETPOLINE_LFENCE & 31)) | \ - (1 << (X86_FEATURE_RETHUNK & 31)) | \ - (1 << (X86_FEATURE_UNRET & 31))) + (1 << (X86_FEATURE_RETPOLINE_LFENCE & 31))) +#endif + +#ifdef CONFIG_RETHUNK +# define DISABLE_RETHUNK 0 +#else +# define DISABLE_RETHUNK (1 << (X86_FEATURE_RETHUNK & 31)) +#endif + +#ifdef CONFIG_CPU_UNRET_ENTRY +# define DISABLE_UNRET 0 +#else +# define DISABLE_UNRET (1 << (X86_FEATURE_UNRET & 31)) #endif
/* Force disable because it's broken beyond repair */ @@ -88,7 +98,7 @@ #define DISABLED_MASK8 0 #define DISABLED_MASK9 (DISABLE_SMAP|DISABLE_SGX) #define DISABLED_MASK10 0 -#define DISABLED_MASK11 (DISABLE_RETPOLINE) +#define DISABLED_MASK11 (DISABLE_RETPOLINE|DISABLE_RETHUNK|DISABLE_UNRET) #define DISABLED_MASK12 0 #define DISABLED_MASK13 0 #define DISABLED_MASK14 0 --- a/arch/x86/include/asm/linkage.h +++ b/arch/x86/include/asm/linkage.h @@ -18,7 +18,7 @@ #define __ALIGN_STR __stringify(__ALIGN) #endif
-#if defined(CONFIG_RETPOLINE) && !defined(__DISABLE_EXPORTS) && !defined(BUILD_VDSO) +#if defined(CONFIG_RETHUNK) && !defined(__DISABLE_EXPORTS) && !defined(BUILD_VDSO) #define RET jmp __x86_return_thunk #else /* CONFIG_RETPOLINE */ #ifdef CONFIG_SLS @@ -30,7 +30,7 @@
#else /* __ASSEMBLY__ */
-#if defined(CONFIG_RETPOLINE) && !defined(__DISABLE_EXPORTS) && !defined(BUILD_VDSO) +#if defined(CONFIG_RETHUNK) && !defined(__DISABLE_EXPORTS) && !defined(BUILD_VDSO) #define ASM_RET "jmp __x86_return_thunk\n\t" #else /* CONFIG_RETPOLINE */ #ifdef CONFIG_SLS --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -127,6 +127,12 @@ .Lskip_rsb_@: .endm
+#ifdef CONFIG_CPU_UNRET_ENTRY +#define CALL_ZEN_UNTRAIN_RET "call zen_untrain_ret" +#else +#define CALL_ZEN_UNTRAIN_RET "" +#endif + /* * Mitigate RETBleed for AMD/Hygon Zen uarch. Requires KERNEL CR3 because the * return thunk isn't mapped into the userspace tables (then again, AMD @@ -139,10 +145,10 @@ * where we have a stack but before any RET instruction. */ .macro UNTRAIN_RET -#ifdef CONFIG_RETPOLINE +#if defined(CONFIG_CPU_UNRET_ENTRY) || defined(CONFIG_CPU_IBPB_ENTRY) ANNOTATE_UNRET_END ALTERNATIVE_2 "", \ - "call zen_untrain_ret", X86_FEATURE_UNRET, \ + CALL_ZEN_UNTRAIN_RET, X86_FEATURE_UNRET, \ "call entry_ibpb", X86_FEATURE_ENTRY_IBPB #endif .endm --- a/arch/x86/include/asm/static_call.h +++ b/arch/x86/include/asm/static_call.h @@ -44,7 +44,7 @@ #define ARCH_DEFINE_STATIC_CALL_TRAMP(name, func) \ __ARCH_DEFINE_STATIC_CALL_TRAMP(name, ".byte 0xe9; .long " #func " - (. + 4)")
-#ifdef CONFIG_RETPOLINE +#ifdef CONFIG_RETHUNK #define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name) \ __ARCH_DEFINE_STATIC_CALL_TRAMP(name, "jmp __x86_return_thunk") #else --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -507,6 +507,7 @@ void __init_or_module noinline apply_ret } }
+#ifdef CONFIG_RETHUNK /* * Rewrite the compiler generated return thunk tail-calls. * @@ -568,6 +569,10 @@ void __init_or_module noinline apply_ret } } } +#else +void __init_or_module noinline apply_returns(s32 *start, s32 *end) { } +#endif /* CONFIG_RETHUNK */ + #else /* !RETPOLINES || !CONFIG_STACK_VALIDATION */
void __init_or_module noinline apply_retpolines(s32 *start, s32 *end) { } --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -888,6 +888,7 @@ static void init_amd_bd(struct cpuinfo_x
void init_spectral_chicken(struct cpuinfo_x86 *c) { +#ifdef CONFIG_CPU_UNRET_ENTRY u64 value;
/* @@ -904,6 +905,7 @@ void init_spectral_chicken(struct cpuinf wrmsrl_safe(MSR_ZEN2_SPECTRAL_CHICKEN, value); } } +#endif }
static void init_amd_zn(struct cpuinfo_x86 *c) --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -835,7 +835,6 @@ static int __init retbleed_parse_cmdline early_param("retbleed", retbleed_parse_cmdline);
#define RETBLEED_UNTRAIN_MSG "WARNING: BTB untrained return thunk mitigation is only effective on AMD/Hygon!\n" -#define RETBLEED_COMPILER_MSG "WARNING: kernel not compiled with RETPOLINE or -mfunction-return capable compiler; falling back to IBPB!\n" #define RETBLEED_INTEL_MSG "WARNING: Spectre v2 mitigation leaves CPU vulnerable to RETBleed attacks, data leaks possible!\n"
static void __init retbleed_select_mitigation(void) @@ -850,18 +849,33 @@ static void __init retbleed_select_mitig return;
case RETBLEED_CMD_UNRET: - retbleed_mitigation = RETBLEED_MITIGATION_UNRET; + if (IS_ENABLED(CONFIG_CPU_UNRET_ENTRY)) { + retbleed_mitigation = RETBLEED_MITIGATION_UNRET; + } else { + pr_err("WARNING: kernel not compiled with CPU_UNRET_ENTRY.\n"); + goto do_cmd_auto; + } break;
case RETBLEED_CMD_IBPB: - retbleed_mitigation = RETBLEED_MITIGATION_IBPB; + if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY)) { + retbleed_mitigation = RETBLEED_MITIGATION_IBPB; + } else { + pr_err("WARNING: kernel not compiled with CPU_IBPB_ENTRY.\n"); + goto do_cmd_auto; + } break;
+do_cmd_auto: case RETBLEED_CMD_AUTO: default: if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD || - boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) - retbleed_mitigation = RETBLEED_MITIGATION_UNRET; + boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) { + if (IS_ENABLED(CONFIG_CPU_UNRET_ENTRY)) + retbleed_mitigation = RETBLEED_MITIGATION_UNRET; + else if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY)) + retbleed_mitigation = RETBLEED_MITIGATION_IBPB; + }
/* * The Intel mitigation (IBRS or eIBRS) was already selected in @@ -874,14 +888,6 @@ static void __init retbleed_select_mitig
switch (retbleed_mitigation) { case RETBLEED_MITIGATION_UNRET: - - if (!IS_ENABLED(CONFIG_RETPOLINE) || - !IS_ENABLED(CONFIG_CC_HAS_RETURN_THUNK)) { - pr_err(RETBLEED_COMPILER_MSG); - retbleed_mitigation = RETBLEED_MITIGATION_IBPB; - goto retbleed_force_ibpb; - } - setup_force_cpu_cap(X86_FEATURE_RETHUNK); setup_force_cpu_cap(X86_FEATURE_UNRET);
@@ -893,7 +899,6 @@ static void __init retbleed_select_mitig break;
case RETBLEED_MITIGATION_IBPB: -retbleed_force_ibpb: setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB); mitigate_smt = true; break; @@ -1264,6 +1269,12 @@ static enum spectre_v2_mitigation_cmd __ return SPECTRE_V2_CMD_AUTO; }
+ if (cmd == SPECTRE_V2_CMD_IBRS && !IS_ENABLED(CONFIG_CPU_IBRS_ENTRY)) { + pr_err("%s selected but not compiled in. Switching to AUTO select\n", + mitigation_options[i].option); + return SPECTRE_V2_CMD_AUTO; + } + if (cmd == SPECTRE_V2_CMD_IBRS && boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) { pr_err("%s selected but not Intel CPU. Switching to AUTO select\n", mitigation_options[i].option); @@ -1321,7 +1332,8 @@ static void __init spectre_v2_select_mit break; }
- if (boot_cpu_has_bug(X86_BUG_RETBLEED) && + if (IS_ENABLED(CONFIG_CPU_IBRS_ENTRY) && + boot_cpu_has_bug(X86_BUG_RETBLEED) && retbleed_cmd != RETBLEED_CMD_OFF && boot_cpu_has(X86_FEATURE_IBRS) && boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) { --- a/arch/x86/kernel/static_call.c +++ b/arch/x86/kernel/static_call.c @@ -120,7 +120,7 @@ void arch_static_call_transform(void *si } EXPORT_SYMBOL_GPL(arch_static_call_transform);
-#ifdef CONFIG_RETPOLINE +#ifdef CONFIG_RETHUNK /* * This is called by apply_returns() to fix up static call trampolines, * specifically ARCH_DEFINE_STATIC_CALL_NULL_TRAMP which is recorded as --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -434,10 +434,10 @@ static int fastop(struct x86_emulate_ctx * Depending on .config the SETcc functions look like: * * SETcc %al [3 bytes] - * RET | JMP __x86_return_thunk [1,5 bytes; CONFIG_RETPOLINE] + * RET | JMP __x86_return_thunk [1,5 bytes; CONFIG_RETHUNK] * INT3 [1 byte; CONFIG_SLS] */ -#define RET_LENGTH (1 + (4 * IS_ENABLED(CONFIG_RETPOLINE)) + \ +#define RET_LENGTH (1 + (4 * IS_ENABLED(CONFIG_RETHUNK)) + \ IS_ENABLED(CONFIG_SLS)) #define SETCC_LENGTH (3 + RET_LENGTH) #define SETCC_ALIGN (4 << ((SETCC_LENGTH > 4) & 1) << ((SETCC_LENGTH > 8) & 1)) --- a/arch/x86/lib/retpoline.S +++ b/arch/x86/lib/retpoline.S @@ -71,6 +71,8 @@ SYM_CODE_END(__x86_indirect_thunk_array) * This function name is magical and is used by -mfunction-return=thunk-extern * for the compiler to generate JMPs to it. */ +#ifdef CONFIG_RETHUNK + .section .text.__x86.return_thunk
/* @@ -135,3 +137,5 @@ SYM_FUNC_END(zen_untrain_ret) __EXPORT_THUNK(zen_untrain_ret)
EXPORT_SYMBOL(__x86_return_thunk) + +#endif /* CONFIG_RETHUNK */ --- a/scripts/Makefile.build +++ b/scripts/Makefile.build @@ -231,6 +231,7 @@ objtool_args = \ $(if $(CONFIG_FRAME_POINTER),, --no-fp) \ $(if $(CONFIG_GCOV_KERNEL)$(CONFIG_LTO_CLANG), --no-unreachable)\ $(if $(CONFIG_RETPOLINE), --retpoline) \ + $(if $(CONFIG_RETHUNK), --rethunk) \ $(if $(CONFIG_X86_SMAP), --uaccess) \ $(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount) \ $(if $(CONFIG_SLS), --sls) --- a/scripts/link-vmlinux.sh +++ b/scripts/link-vmlinux.sh @@ -120,7 +120,7 @@ objtool_link()
if [ -n "${CONFIG_VMLINUX_VALIDATION}" ]; then objtoolopt="${objtoolopt} --noinstr" - if is_enabled CONFIG_RETPOLINE; then + if is_enabled CONFIG_CPU_UNRET_ENTRY; then objtoolopt="${objtoolopt} --unret" fi fi --- a/security/Kconfig +++ b/security/Kconfig @@ -54,17 +54,6 @@ config SECURITY_NETWORK implement socket and networking access controls. If you are unsure how to answer this question, answer N.
-config PAGE_TABLE_ISOLATION - bool "Remove the kernel mapping in user mode" - default y - depends on (X86_64 || X86_PAE) && !UML - help - This feature reduces the number of hardware side channels by - ensuring that the majority of kernel addresses are not mapped - into userspace. - - See Documentation/x86/pti.rst for more details. - config SECURITY_INFINIBAND bool "Infiniband Security Hooks" depends on SECURITY && INFINIBAND --- a/tools/objtool/builtin-check.c +++ b/tools/objtool/builtin-check.c @@ -20,7 +20,7 @@ #include <objtool/objtool.h>
bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats, - validate_dup, vmlinux, mcount, noinstr, backup, sls, unret; + validate_dup, vmlinux, mcount, noinstr, backup, sls, unret, rethunk;
static const char * const check_usage[] = { "objtool check [<options>] file.o", @@ -36,6 +36,7 @@ const struct option check_options[] = { OPT_BOOLEAN('f', "no-fp", &no_fp, "Skip frame pointer validation"), OPT_BOOLEAN('u', "no-unreachable", &no_unreachable, "Skip 'unreachable instruction' warnings"), OPT_BOOLEAN('r', "retpoline", &retpoline, "Validate retpoline assumptions"), + OPT_BOOLEAN(0, "rethunk", &rethunk, "validate and annotate rethunk usage"), OPT_BOOLEAN(0, "unret", &unret, "validate entry unret placement"), OPT_BOOLEAN('m', "module", &module, "Indicates the object will be part of a kernel module"), OPT_BOOLEAN('b', "backtrace", &backtrace, "unwind on error"), --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -3440,8 +3440,11 @@ static int validate_retpoline(struct obj continue;
if (insn->type == INSN_RETURN) { - WARN_FUNC("'naked' return found in RETPOLINE build", - insn->sec, insn->offset); + if (rethunk) { + WARN_FUNC("'naked' return found in RETHUNK build", + insn->sec, insn->offset); + } else + continue; } else { WARN_FUNC("indirect %s found in RETPOLINE build", insn->sec, insn->offset, @@ -3711,7 +3714,9 @@ int check(struct objtool_file *file) if (ret < 0) goto out; warnings += ret; + }
+ if (rethunk) { ret = create_return_sites_sections(file); if (ret < 0) goto out; --- a/tools/objtool/include/objtool/builtin.h +++ b/tools/objtool/include/objtool/builtin.h @@ -9,7 +9,7 @@
extern const struct option check_options[]; extern bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats, - validate_dup, vmlinux, mcount, noinstr, backup, sls, unret; + validate_dup, vmlinux, mcount, noinstr, backup, sls, unret, rethunk;
extern int cmd_parse_options(int argc, const char **argv, const char * const usage[]);