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From:   Lai Jiangshan <laijs@linux.alibaba.com>
To:     linux-kernel@vger.kernel.org
Cc:     Lai Jiangshan <laijs@linux.alibaba.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>, x86@kernel.org,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Alexandre Chartre <alexandre.chartre@oracle.com>
Subject: [RFC PATCH V2 3/7] x86/hw_breakpoint: Prevent data breakpoints on per_cpu cpu_tss_rw
Date:   Tue, 26 May 2020 01:42:17 +0000
Message-Id: <20200526014221.2119-4-laijs@linux.alibaba.com>
In-Reply-To: <20200526014221.2119-1-laijs@linux.alibaba.com>
References: <20200525152517.GY325280@hirez.programming.kicks-ass.net>
 <20200526014221.2119-1-laijs@linux.alibaba.com>
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cpu_tss_rw is not directly referenced by hardware, but
cpu_tss_rw is also used in CPU entry code, especially
when #DB shifts its stacks. If a data breakpoint is on
the cpu_tss_rw.x86_tss.ist[IST_INDEX_DB], it will cause
recursive #DB (and then #DF soon for #DB is generated
after the access, IST-shifting, is done).

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86@kernel.org
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 arch/x86/kernel/hw_breakpoint.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
index f859095c1b6c..7d3966b9aa12 100644
--- a/arch/x86/kernel/hw_breakpoint.c
+++ b/arch/x86/kernel/hw_breakpoint.c
@@ -255,6 +255,19 @@ static inline bool within_cpu_entry(unsigned long addr, unsigned long end)
 		if (within_area(addr, end, (unsigned long)get_cpu_gdt_rw(cpu),
 				GDT_SIZE))
 			return true;
+
+		/*
+		 * cpu_tss_rw is not directly referenced by hardware, but
+		 * cpu_tss_rw is also used in CPU entry code, especially
+		 * when #DB shifts its stacks. If a data breakpoint is on
+		 * the cpu_tss_rw.x86_tss.ist[IST_INDEX_DB], it will cause
+		 * recursive #DB (and then #DF soon for #DB is generated
+		 * after the access, IST-shifting, is done).
+		 */
+		if (within_area(addr, end,
+				(unsigned long)&per_cpu(cpu_tss_rw, cpu),
+				sizeof(struct tss_struct)))
+			return true;
 	}
 
 	return false;
-- 
2.20.1