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Subject[PATCH 2/2] x86/hw_breakpoint: Prevent data breakpoints on cpu_dr7
Date
From: Lai Jiangshan <laijs@linux.alibaba.com>

When in guest (X86_FEATURE_HYPERVISOR), local_db_save() will read
per-cpu cpu_dr7 before clear dr7 register.

local_db_save() is called at the start of exc_debug_kernel().
To avoid recursive #DB, we have to disallow data breakpoints
on cpu_dr7.

Fixes: 84b6a3491567a("x86/entry: Optimize local_db_save() for virt")
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
arch/x86/kernel/hw_breakpoint.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
index bc7493a0736f..de34dd49d317 100644
--- a/arch/x86/kernel/hw_breakpoint.c
+++ b/arch/x86/kernel/hw_breakpoint.c
@@ -307,6 +307,14 @@ static inline bool within_cpu_entry(unsigned long addr, unsigned long end)
(unsigned long)&per_cpu(cpu_tlbstate, cpu),
sizeof(struct tlb_state)))
return true;
+
+ /*
+ * When in guest (X86_FEATURE_HYPERVISOR), local_db_save()
+ * will read per-cpu cpu_dr7 before clear dr7 register.
+ */
+ if (within_area(addr, end, (unsigned long)&per_cpu(cpu_dr7, cpu),
+ sizeof(cpu_dr7)))
+ return true;
}

return false;
--
2.19.1.6.gb485710b
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