Commit e35123d8 authored by Will Deacon's avatar Will Deacon

arm64: lto: Strengthen READ_ONCE() to acquire when CONFIG_LTO=y

When building with LTO, there is an increased risk of the compiler
converting an address dependency headed by a READ_ONCE() invocation
into a control dependency and consequently allowing for harmful
reordering by the CPU.

Ensure that such transformations are harmless by overriding the generic
READ_ONCE() definition with one that provides acquire semantics when
building with LTO.
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent 5af76fb4
/* SPDX-License-Identifier: GPL-2.0 */
/*
* Copyright (C) 2020 Google LLC.
*/
#ifndef __ASM_RWONCE_H
#define __ASM_RWONCE_H
#ifdef CONFIG_LTO
#include <linux/compiler_types.h>
#include <asm/alternative-macros.h>
#ifndef BUILD_VDSO
#ifdef CONFIG_AS_HAS_LDAPR
#define __LOAD_RCPC(sfx, regs...) \
ALTERNATIVE( \
"ldar" #sfx "\t" #regs, \
".arch_extension rcpc\n" \
"ldapr" #sfx "\t" #regs, \
ARM64_HAS_LDAPR)
#else
#define __LOAD_RCPC(sfx, regs...) "ldar" #sfx "\t" #regs
#endif /* CONFIG_AS_HAS_LDAPR */
/*
* When building with LTO, there is an increased risk of the compiler
* converting an address dependency headed by a READ_ONCE() invocation
* into a control dependency and consequently allowing for harmful
* reordering by the CPU.
*
* Ensure that such transformations are harmless by overriding the generic
* READ_ONCE() definition with one that provides RCpc acquire semantics
* when building with LTO.
*/
#define __READ_ONCE(x) \
({ \
typeof(&(x)) __x = &(x); \
int atomic = 1; \
union { __unqual_scalar_typeof(*__x) __val; char __c[1]; } __u; \
switch (sizeof(x)) { \
case 1: \
asm volatile(__LOAD_RCPC(b, %w0, %1) \
: "=r" (*(__u8 *)__u.__c) \
: "Q" (*__x) : "memory"); \
break; \
case 2: \
asm volatile(__LOAD_RCPC(h, %w0, %1) \
: "=r" (*(__u16 *)__u.__c) \
: "Q" (*__x) : "memory"); \
break; \
case 4: \
asm volatile(__LOAD_RCPC(, %w0, %1) \
: "=r" (*(__u32 *)__u.__c) \
: "Q" (*__x) : "memory"); \
break; \
case 8: \
asm volatile(__LOAD_RCPC(, %0, %1) \
: "=r" (*(__u64 *)__u.__c) \
: "Q" (*__x) : "memory"); \
break; \
default: \
atomic = 0; \
} \
atomic ? (typeof(*__x))__u.__val : (*(volatile typeof(__x))__x);\
})
#endif /* !BUILD_VDSO */
#endif /* CONFIG_LTO */
#include <asm-generic/rwonce.h>
#endif /* __ASM_RWONCE_H */
...@@ -28,7 +28,7 @@ ldflags-y := -shared -nostdlib -soname=linux-vdso.so.1 --hash-style=sysv \ ...@@ -28,7 +28,7 @@ ldflags-y := -shared -nostdlib -soname=linux-vdso.so.1 --hash-style=sysv \
$(btildflags-y) -T $(btildflags-y) -T
ccflags-y := -fno-common -fno-builtin -fno-stack-protector -ffixed-x18 ccflags-y := -fno-common -fno-builtin -fno-stack-protector -ffixed-x18
ccflags-y += -DDISABLE_BRANCH_PROFILING ccflags-y += -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os $(CC_FLAGS_SCS) $(GCC_PLUGINS_CFLAGS) CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os $(CC_FLAGS_SCS) $(GCC_PLUGINS_CFLAGS)
KASAN_SANITIZE := n KASAN_SANITIZE := n
......
...@@ -48,7 +48,7 @@ cc32-as-instr = $(call try-run,\ ...@@ -48,7 +48,7 @@ cc32-as-instr = $(call try-run,\
# As a result we set our own flags here. # As a result we set our own flags here.
# KBUILD_CPPFLAGS and NOSTDINC_FLAGS from top-level Makefile # KBUILD_CPPFLAGS and NOSTDINC_FLAGS from top-level Makefile
VDSO_CPPFLAGS := -D__KERNEL__ -nostdinc -isystem $(shell $(CC_COMPAT) -print-file-name=include) VDSO_CPPFLAGS := -DBUILD_VDSO -D__KERNEL__ -nostdinc -isystem $(shell $(CC_COMPAT) -print-file-name=include)
VDSO_CPPFLAGS += $(LINUXINCLUDE) VDSO_CPPFLAGS += $(LINUXINCLUDE)
# Common C and assembly flags # Common C and assembly flags
......
...@@ -201,7 +201,7 @@ SECTIONS ...@@ -201,7 +201,7 @@ SECTIONS
INIT_CALLS INIT_CALLS
CON_INITCALL CON_INITCALL
INIT_RAM_FS INIT_RAM_FS
*(.init.rodata.* .init.bss) /* from the EFI stub */ *(.init.altinstructions .init.rodata.* .init.bss) /* from the EFI stub */
} }
.exit.data : { .exit.data : {
EXIT_DATA EXIT_DATA
......
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