The following commit has been merged into the x86/urgent branch of tip:

Commit-ID: 3943abf2dbfae9ea4d2da05c1db569a0603f76da Gitweb: https://git.kernel.org/tip/3943abf2dbfae9ea4d2da05c1db569a0603f76da Author: Lai Jiangshan laijs@linux.alibaba.com AuthorDate: Thu, 04 Feb 2021 23:27:07 +08:00 Committer: Thomas Gleixner tglx@linutronix.de CommitterDate: Fri, 05 Feb 2021 20:13:12 +01:00

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: 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

--- 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 012ed82..668a4a6 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;