Commit 3943abf2 authored by Lai Jiangshan's avatar Lai Jiangshan Committed by Thomas Gleixner
Browse files

x86/debug: Prevent data breakpoints on cpu_dr7 



local_db_save() is called at the start of exc_debug_kernel(), reads DR7 and
disables breakpoints to prevent recursion.

When running in a guest (X86_FEATURE_HYPERVISOR), local_db_save() reads the
per-cpu variable cpu_dr7 to check whether a breakpoint is active or not
before it accesses DR7.

A data breakpoint on cpu_dr7 therefore results in infinite #DB recursion.

Disallow data breakpoints on cpu_dr7 to prevent that.

Fixes: 84b6a349("x86/entry: Optimize local_db_save() for virt")
Signed-off-by: default avatarLai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210204152708.21308-2-jiangshanlai@gmail.com
parent c4bed4b9

arch/x86/kernel/hw_breakpoint.c

+8 −0
Original line number Diff line number Diff line
@@ -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;