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

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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: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Will Deacon
2020-06-30 14:02:48 +01:00
parent 5af76fb422
commit e35123d83e
4 changed files with 76 additions and 3 deletions
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2
arch/arm64/kernel/vdso32/Makefile
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@@ -48,7 +48,7 @@ cc32-as-instr = $(call try-run,\
# As a result we set our own flags here.
# 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)
# Common C and assembly flags