From: Andrey Ryabinin <a.ryabinin@samsung.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrey Ryabinin <a.ryabinin@samsung.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Konstantin Serebryany <kcc@google.com>,
        Dmitry Chernenkov <dmitryc@google.com>,
        Andrey Konovalov <adech.fo@gmail.com>,
        Yuri Gribov <tetra2005@gmail.com>,
        Konstantin Khlebnikov <koct9i@gmail.com>,
        Sasha Levin <sasha.levin@oracle.com>, Christoph Lameter <cl@linux.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Dave Hansen <dave.hansen@intel.com>, Andi Kleen <andi@firstfloor.org>,
        Vegard Nossum <vegard.nossum@gmail.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Dave Jones <davej@redhat.com>,
        x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>
Subject: [PATCH v7 02/12] x86_64: load_percpu_segment: read
 irq_stack_union.gs_base before load_segment
Date: Mon, 24 Nov 2014 21:02:15 +0300
Message-id: <1416852146-9781-3-git-send-email-a.ryabinin@samsung.com>
In-reply-to: <1416852146-9781-1-git-send-email-a.ryabinin@samsung.com>
References: <1404905415-9046-1-git-send-email-a.ryabinin@samsung.com>
 <1416852146-9781-1-git-send-email-a.ryabinin@samsung.com>
Sender: linux-kernel-owner@vger.kernel.org

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 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);
 #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();
 }
-- 
2.1.3

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