x86/hw_breakpoint: Prevent data breakpoints on user_pcid_flush_mask

The per-CPU user_pcid_flush_mask is used in the low level entry code. A
data breakpoint can cause #DB recursion.

Protect the full cpu_tlbstate structure for simplicity.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200526014221.2119-5-laijs@linux.alibaba.com
Link: https://lkml.kernel.org/r/20200529213320.955117574@infradead.org

diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
index f311bbf..fc1743a 100644 (file)
--- a/arch/x86/kernel/hw_breakpoint.c
+++ b/arch/x86/kernel/hw_breakpoint.c
@@ -33,6 +33,7 @@
 #include <asm/debugreg.h>
 #include <asm/user.h>
 #include <asm/desc.h>
+#include <asm/tlbflush.h>
 
 /* Per cpu debug control register value */
 DEFINE_PER_CPU(unsigned long, cpu_dr7);
@@ -264,6 +265,16 @@ static inline bool within_cpu_entry(unsigned long addr, unsigned long end)
                                (unsigned long)&per_cpu(cpu_tss_rw, cpu),
                                sizeof(struct tss_struct)))
                        return true;
+
+               /*
+                * cpu_tlbstate.user_pcid_flush_mask is used for CPU entry.
+                * If a data breakpoint on it, it will cause an unwanted #DB.
+                * Protect the full cpu_tlbstate structure to be sure.
+                */
+               if (within_area(addr, end,
+                               (unsigned long)&per_cpu(cpu_tlbstate, cpu),
+                               sizeof(struct tlb_state)))
+                       return true;
        }
 
        return false;