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x86/debug: Prevent data breakpoints on cpu_dr7

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commit 3943abf2dbfae9ea4d2da05c1db569a0603f76da upstream.

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: 84b6a3491567a("x86/entry: Optimize local_db_save() for virt")
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210204152708.21308-2-jiangshanlai@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Lai Jiangshan 2021-02-04 23:27:07 +08:00 committed by Greg Kroah-Hartman
parent b796770c6d
commit 3dcf233b58
1 changed files with 8 additions and 0 deletions
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8
arch/x86/kernel/hw_breakpoint.c
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@ -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;