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Subject[PATCH 1/2] x86/hw_breakpoint: Prevent data breakpoints on __per_cpu_offset
Date
From: Lai Jiangshan <laijs@linux.alibaba.com>

When FSGSBASE is enabled, paranoid_entry() fetches the per-CPU
GSBASE value via __per_cpu_offset or pcpu_unit_offsets.

When data breakpoint is set on __per_cpu_offset[cpu] (read-write
operation), the specific cpu will be stuck in the infinite #DB loop.
RCU will try to send NMI to the specific cpu, but it is not working
either since NMI also relies on paranoid_entry().

Fixes: eaad981291ee3("x86/entry/64: Introduce the FIND_PERCPU_BASE macro")
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
arch/x86/kernel/hw_breakpoint.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
index 03aa33b58165..bc7493a0736f 100644
--- a/arch/x86/kernel/hw_breakpoint.c
+++ b/arch/x86/kernel/hw_breakpoint.c
@@ -269,6 +269,20 @@ static inline bool within_cpu_entry(unsigned long addr, unsigned long end)
CPU_ENTRY_AREA_TOTAL_SIZE))
return true;

+ /*
+ * When FSGSBASE is enabled, paranoid_entry() fetches the per-CPU
+ * GSBASE value via __per_cpu_offset or pcpu_unit_offsets.
+ */
+#ifdef CONFIG_SMP
+ if (within_area(addr, end, (unsigned long)__per_cpu_offset,
+ sizeof(unsigned long) * nr_cpu_ids))
+ return true;
+#else
+ if (within_area(addr, end, (unsigned long)&pcpu_unit_offsets,
+ sizeof(pcpu_unit_offsets)))
+ return true;
+#endif
+
for_each_possible_cpu(cpu) {
/* The original rw GDT is being used after load_direct_gdt() */
if (within_area(addr, end, (unsigned long)get_cpu_gdt_rw(cpu),
--
2.19.1.6.gb485710b
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