linux-kernel - [PATCH 04/14] x86/hw_breakpoint: Prevent data breakpoints on user_pcid_flush

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Date:   Fri, 29 May 2020 23:27:32 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     tglx@...utronix.de, luto@...capital.net, peterz@...radead.org
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        sean.j.christopherson@...el.com, andrew.cooper3@...rix.com,
        daniel.thompson@...aro.org, a.darwish@...utronix.de,
        rostedt@...dmis.org, bigeasy@...utronix.de
Subject: [PATCH 04/14] x86/hw_breakpoint: Prevent data breakpoints on user_pcid_flush_mask

From: Lai Jiangshan <laijs@...ux.alibaba.com>

The percpu 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.

There are some other percpu data used in CPU entry, but they are
either in already-protected cpu_tss_rw or are safe to trigger #DB
(espfix_waddr, espfix_stack).

Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20200526014221.2119-5-laijs@linux.alibaba.com
---
 arch/x86/kernel/hw_breakpoint.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

--- 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(unsi
 				(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;