| From | Andrey Ryabinin <> | Subject | [PATCH v4 03/13] x86_64: load_percpu_segment: read irq_stack_union.gs_base before load_segment | Date | Mon, 06 Oct 2014 19:53:57 +0400 |
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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 <a.ryabinin@samsung.com> --- 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 ea51f2c..8d9a3c6 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); #else + 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); #endif load_stack_canary_segment(); } -- 2.1.2
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