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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.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20211204134908.140103474@infradead.org
This commit is contained in:
Peter Zijlstra 2021-12-04 14:43:44 +01:00 committed by Borislav Petkov
parent 26c44b776d
commit e463a09af2
10 changed files with 38 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
arch/x86/Kconfig
View File

@ -472,6 +472,18 @@ config RETPOLINE
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 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)

4
arch/x86/Makefile
View File

@ -191,6 +191,10 @@ ifdef CONFIG_RETPOLINE
endif
endif
ifdef CONFIG_SLS
KBUILD_CFLAGS += -mharden-sls=all
endif
KBUILD_LDFLAGS += -m elf_$(UTS_MACHINE)
ifdef CONFIG_LTO_CLANG

10
arch/x86/include/asm/linkage.h
View File

@ -18,9 +18,19 @@
#define __ALIGN_STR __stringify(__ALIGN)
#endif
#ifdef CONFIG_SLS
#define RET ret; int3
#else
#define RET ret
#endif
#else /* __ASSEMBLY__ */
#ifdef CONFIG_SLS
#define ASM_RET "ret; int3\n\t"
#else
#define ASM_RET "ret\n\t"
#endif
#endif /* __ASSEMBLY__ */

2
arch/x86/include/asm/static_call.h
View File

@ -36,7 +36,7 @@
__ARCH_DEFINE_STATIC_CALL_TRAMP(name, ".byte 0xe9; .long " #func " - (. + 4)")
#define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name) \
__ARCH_DEFINE_STATIC_CALL_TRAMP(name, "ret; nop; nop; nop; nop")
__ARCH_DEFINE_STATIC_CALL_TRAMP(name, "ret; int3; nop; nop; nop")
#define ARCH_ADD_TRAMP_KEY(name) \

2
arch/x86/kernel/ftrace.c
View File

@ -303,7 +303,7 @@ union ftrace_op_code_union {
} __attribute__((packed));
};
#define RET_SIZE 1
#define RET_SIZE 1 + IS_ENABLED(CONFIG_SLS)
static unsigned long
create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)

5
arch/x86/kernel/static_call.c
View File

@ -17,6 +17,8 @@ enum insn_type {
*/
static const u8 xor5rax[] = { 0x66, 0x66, 0x48, 0x31, 0xc0 };
static const u8 retinsn[] = { RET_INSN_OPCODE, 0xcc, 0xcc, 0xcc, 0xcc };
static void __ref __static_call_transform(void *insn, enum insn_type type, void *func)
{
const void *emulate = NULL;
@ -42,8 +44,7 @@ static void __ref __static_call_transform(void *insn, enum insn_type type, void
break;
case RET:
code = text_gen_insn(RET_INSN_OPCODE, insn, func);
size = RET_INSN_SIZE;
code = &retinsn;
break;
}

2
arch/x86/lib/memmove_64.S
View File

@ -40,7 +40,7 @@ SYM_FUNC_START(__memmove)
/* FSRM implies ERMS => no length checks, do the copy directly */
.Lmemmove_begin_forward:
ALTERNATIVE "cmp $0x20, %rdx; jb 1f", "", X86_FEATURE_FSRM
ALTERNATIVE "", "movq %rdx, %rcx; rep movsb; RET", X86_FEATURE_ERMS
ALTERNATIVE "", __stringify(movq %rdx, %rcx; rep movsb; RET), X86_FEATURE_ERMS
/*
* movsq instruction have many startup latency

2
arch/x86/lib/retpoline.S
View File

@ -34,7 +34,7 @@ SYM_INNER_LABEL(__x86_indirect_thunk_\reg, SYM_L_GLOBAL)
ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \
__stringify(RETPOLINE \reg), X86_FEATURE_RETPOLINE, \
__stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), X86_FEATURE_RETPOLINE_AMD
__stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg; int3), X86_FEATURE_RETPOLINE_AMD
.endm

3
scripts/Makefile.build
View File

@ -234,7 +234,8 @@ objtool_args = \
$(if $(CONFIG_GCOV_KERNEL)$(CONFIG_LTO_CLANG), --no-unreachable)\
$(if $(CONFIG_RETPOLINE), --retpoline) \
$(if $(CONFIG_X86_SMAP), --uaccess) \
$(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount)
$(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount) \
$(if $(CONFIG_SLS), --sls)
cmd_objtool = $(if $(objtool-enabled), ; $(objtool) $(objtool_args) $@)
cmd_gen_objtooldep = $(if $(objtool-enabled), { echo ; echo '$@: $$(wildcard $(objtool))' ; } >> $(dot-target).cmd)

3
scripts/link-vmlinux.sh
View File

@ -139,6 +139,9 @@ objtool_link()
if [ -n "${CONFIG_X86_SMAP}" ]; then
objtoolopt="${objtoolopt} --uaccess"
fi
if [ -n "${CONFIG_SLS}" ]; then
objtoolopt="${objtoolopt} --sls"
fi
info OBJTOOL ${1}
tools/objtool/objtool ${objtoolcmd} ${objtoolopt} ${1}
fi