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Subject[tip: x86/core] x86: Add straight-line-speculation mitigation
The following commit has been merged into the x86/core branch of tip:

Commit-ID: e463a09af2f0677b9485a7e8e4e70b396b2ffb6f
Gitweb: https://git.kernel.org/tip/e463a09af2f0677b9485a7e8e4e70b396b2ffb6f
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Sat, 04 Dec 2021 14:43:44 +01:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Thu, 09 Dec 2021 13:32:25 +01:00

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
---
arch/x86/Kconfig | 12 ++++++++++++
arch/x86/Makefile | 4 ++++
arch/x86/include/asm/linkage.h | 10 ++++++++++
arch/x86/include/asm/static_call.h | 2 +-
arch/x86/kernel/ftrace.c | 2 +-
arch/x86/kernel/static_call.c | 5 +++--
arch/x86/lib/memmove_64.S | 2 +-
arch/x86/lib/retpoline.S | 2 +-
scripts/Makefile.build | 3 ++-
scripts/link-vmlinux.sh | 3 +++
10 files changed, 38 insertions(+), 7 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 7399327..dd13ba8 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -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)
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index c38b657..e84cdd4 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -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
diff --git a/arch/x86/include/asm/linkage.h b/arch/x86/include/asm/linkage.h
index ebddec2..0309079 100644
--- a/arch/x86/include/asm/linkage.h
+++ b/arch/x86/include/asm/linkage.h
@@ -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__ */

diff --git a/arch/x86/include/asm/static_call.h b/arch/x86/include/asm/static_call.h
index 39ebe05..ed4f8bb 100644
--- a/arch/x86/include/asm/static_call.h
+++ b/arch/x86/include/asm/static_call.h
@@ -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) \
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index c39f906..7cc540e 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -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)
diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c
index 9c407a3..531fb4c 100644
--- a/arch/x86/kernel/static_call.c
+++ b/arch/x86/kernel/static_call.c
@@ -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;
}

diff --git a/arch/x86/lib/memmove_64.S b/arch/x86/lib/memmove_64.S
index e84d649..50ea390 100644
--- a/arch/x86/lib/memmove_64.S
+++ b/arch/x86/lib/memmove_64.S
@@ -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
diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index a842866..89b3fb2 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -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

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 78656b5..a4b89b7 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -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))' ; } >> $(dot-target).cmd)
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 5cdd9bc..9716f28 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -139,6 +139,9 @@ objtool_link()
if [ -n "${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
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