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x86: Add straight-line-speculation mitigation

Make use of an upcoming GCC feature to mitigate straight-line-speculation for x86: https://gcc.gnu.org/g:53a643f8568067d7700a9f2facc8ba39974973d3 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102952 https://bugs.llvm.org/show_bug.cgi?id=52323 It's built tested on x86_64-allyesconfig using GCC-12 and GCC-11. Maintenance overhead of this should be fairly low due to objtool validation. Size overhead of all these additional int3 instructions comes to: text data bss dec hex filename 22267751 6933356 2011368 31212475 1dc43bb defconfig-build/vmlinux 22804126 6933356 1470696 31208178 1dc32f2 defconfig-build/vmlinux.sls Or roughly 2.4% additional text.

Peter Zijlstra committed 4 years ago

Commit e463a091 parent 26c44b710 files · +38 −7Browse files

Unified · Split

10 files
  1. arch/x86/Kconfig +12 −0
  2. arch/x86/Makefile +4 −0
  3. arch/x86/include/asm/linkage.h +10 −0
  4. arch/x86/include/asm/static_call.h +1 −1
  5. arch/x86/kernel/ftrace.c +1 −1
  6. arch/x86/kernel/static_call.c +3 −2
  7. arch/x86/lib/memmove_64.S +1 −1
  8. arch/x86/lib/retpoline.S +1 −1
  9. scripts/Makefile.build +2 −1
  10. scripts/link-vmlinux.sh +3 −0
arch/x86/Kconfig+12−0
@@ -472,6 +472,18 @@ config RETPOLINE · 471 unmodified lines
472472 branches. Requires a compiler with -mindirect-branch=thunk-extern
473473 support for full protection. The kernel may run slower.
474474
475+config CC_HAS_SLS
476+ def_bool $(cc-option,-mharden-sls=all)
477+
478+config SLS
479+ bool "Mitigate Straight-Line-Speculation"
480+ depends on CC_HAS_SLS && X86_64
481+ default n
482+ help
483+ Compile the kernel with straight-line-speculation options to guard
484+ against straight line speculation. The kernel image might be slightly
485+ larger.
486+
475487 config X86_CPU_RESCTRL
476488 bool "x86 CPU resource control support"
477489 depends on X86 && (CPU_SUP_INTEL || CPU_SUP_AMD)
arch/x86/Makefile+4−0
@@ -191,6 +191,10 @@ ifdef CONFIG_RETPOLINE · 190 unmodified lines
191191 endif
192192 endif
193193
194+ifdef CONFIG_SLS
195+ KBUILD_CFLAGS += -mharden-sls=all
196+endif
197+
194198 KBUILD_LDFLAGS += -m elf_$(UTS_MACHINE)
195199
196200 ifdef CONFIG_LTO_CLANG
arch/x86/include/asm/linkage.h+10−0
@@ -18,9 +18,19 @@ · 17 unmodified lines
1818 #define __ALIGN_STR __stringify(__ALIGN)
1919 #endif
2020
21+#ifdef CONFIG_SLS
22+#define RET ret; int3
23+#else
24+#define RET ret
25+#endif
26+
2127 #else /* __ASSEMBLY__ */
2228
29+#ifdef CONFIG_SLS
30+#define ASM_RET "ret; int3\n\t"
31+#else
2332 #define ASM_RET "ret\n\t"
33+#endif
2434
2535 #endif /* __ASSEMBLY__ */
2636
arch/x86/include/asm/static_call.h+1−1
@@ -36,7 +36,7 @@ · 35 unmodified lines
3636 __ARCH_DEFINE_STATIC_CALL_TRAMP(name, ".byte 0xe9; .long " #func " - (. + 4)")
3737
3838 #define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name) \
39− __ARCH_DEFINE_STATIC_CALL_TRAMP(name, "ret; nop; nop; nop; nop")
39+ __ARCH_DEFINE_STATIC_CALL_TRAMP(name, "ret; int3; nop; nop; nop")
4040
4141
4242 #define ARCH_ADD_TRAMP_KEY(name) \
arch/x86/kernel/ftrace.c+1−1
@@ -303,7 +303,7 @@ union ftrace_op_code_union { · 302 unmodified lines
303303 } __attribute__((packed));
304304 };
305305
306−#define RET_SIZE 1
306+#define RET_SIZE 1 + IS_ENABLED(CONFIG_SLS)
307307
308308 static unsigned long
309309 create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
arch/x86/kernel/static_call.c+3−2
@@ -17,6 +17,8 @@ enum insn_type { · 16 unmodified lines
1717 */
1818 static const u8 xor5rax[] = { 0x66, 0x66, 0x48, 0x31, 0xc0 };
1919
20+static const u8 retinsn[] = { RET_INSN_OPCODE, 0xcc, 0xcc, 0xcc, 0xcc };
21+
2022 static void __ref __static_call_transform(void *insn, enum insn_type type, void *func)
2123 {
2224 const void *emulate = NULL;
@@ -42,8 +44,7 @@ static void __ref __static_call_transform(void *insn, enum insn_type type, void · 19 unmodified lines
4244 break;
4345
4446 case RET:
45− code = text_gen_insn(RET_INSN_OPCODE, insn, func);
46− size = RET_INSN_SIZE;
47+ code = &retinsn;
4748 break;
4849 }
4950
arch/x86/lib/memmove_64.S+1−1
@@ -40,7 +40,7 @@ SYM_FUNC_START(__memmove) · 39 unmodified lines
4040 /* FSRM implies ERMS => no length checks, do the copy directly */
4141 .Lmemmove_begin_forward:
4242 ALTERNATIVE "cmp $0x20, %rdx; jb 1f", "", X86_FEATURE_FSRM
43− ALTERNATIVE "", "movq %rdx, %rcx; rep movsb; RET", X86_FEATURE_ERMS
43+ ALTERNATIVE "", __stringify(movq %rdx, %rcx; rep movsb; RET), X86_FEATURE_ERMS
4444
4545 /*
4646 * movsq instruction have many startup latency
arch/x86/lib/retpoline.S+1−1
@@ -34,7 +34,7 @@ SYM_INNER_LABEL(__x86_indirect_thunk_\reg, SYM_L_GLOBAL) · 33 unmodified lines
3434
3535 ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \
3636 __stringify(RETPOLINE \reg), X86_FEATURE_RETPOLINE, \
37− __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), X86_FEATURE_RETPOLINE_AMD
37+ __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg; int3), X86_FEATURE_RETPOLINE_AMD
3838
3939 .endm
4040
scripts/Makefile.build+2−1
@@ -234,7 +234,8 @@ objtool_args = \ · 233 unmodified lines
234234 $(if $(CONFIG_GCOV_KERNEL)$(CONFIG_LTO_CLANG), --no-unreachable)\
235235 $(if $(CONFIG_RETPOLINE), --retpoline) \
236236 $(if $(CONFIG_X86_SMAP), --uaccess) \
237− $(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount)
237+ $(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount) \
238+ $(if $(CONFIG_SLS), --sls)
238239
239240 cmd_objtool = $(if $(objtool-enabled), ; $(objtool) $(objtool_args) $@)
240241 cmd_gen_objtooldep = $(if $(objtool-enabled), { echo ; echo '$@: $$(wildcard $(objtool))' ; } >> $(dot-target).cmd)
scripts/link-vmlinux.sh+3−0
@@ -139,6 +139,9 @@ objtool_link() · 138 unmodified lines
139139 if [ -n "${CONFIG_X86_SMAP}" ]; then
140140 objtoolopt="${objtoolopt} --uaccess"
141141 fi
142+ if [ -n "${CONFIG_SLS}" ]; then
143+ objtoolopt="${objtoolopt} --sls"
144+ fi
142145 info OBJTOOL ${1}
143146 tools/objtool/objtool ${objtoolcmd} ${objtoolopt} ${1}
144147 fi