[RFC PATCH 3/5] x86/hw_breakpoint: Prevent data breakpoints on per_cpu cpu_tss_rw

[Lai Jiangshan]

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@xxxxxxxxxx>
Cc: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
---
 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