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Subject[PATCH v7 02/12] x86_64: load_percpu_segment: read irq_stack_union.gs_base before load_segment
Reading irq_stack_union.gs_base after load_segment creates troubles for kasan.
Compiler inserts __asan_load in between load_segment and wrmsrl. If kernel
built with stackprotector this will result in boot failure because __asan_load
has stackprotector.

To avoid this irq_stack_union.gs_base stored to temporary variable before
load_segment, so __asan_load will be called before load_segment().

There are two alternative ways to fix this:
a) Add __attribute__((no_sanitize_address)) to load_percpu_segment(),
which tells compiler to not instrument this function. However this
will result in build failure with CONFIG_KASAN=y and CONFIG_OPTIMIZE_INLINING=y.

b) Add -fno-stack-protector for mm/kasan/kasan.c

Signed-off-by: Andrey Ryabinin <>
arch/x86/kernel/cpu/common.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 8779d63..97f56f6 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -389,8 +389,10 @@ void load_percpu_segment(int cpu)
#ifdef CONFIG_X86_32
loadsegment(fs, __KERNEL_PERCPU);
+ void *gs_base = per_cpu(irq_stack_union.gs_base, cpu);
loadsegment(gs, 0);
- wrmsrl(MSR_GS_BASE, (unsigned long)per_cpu(irq_stack_union.gs_base, cpu));
+ wrmsrl(MSR_GS_BASE, (unsigned long)gs_base);

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