Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 5.10 109/120] x86/debug: Prevent data breakpoints on cpu_dr7 | Date | Mon, 8 Feb 2021 16:01:36 +0100 |
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From: Lai Jiangshan <laijs@linux.alibaba.com>
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> --- arch/x86/kernel/hw_breakpoint.c | 8 ++++++++ 1 file changed, 8 insertions(+)
--- a/arch/x86/kernel/hw_breakpoint.c +++ b/arch/x86/kernel/hw_breakpoint.c @@ -307,6 +307,14 @@ static inline bool within_cpu_entry(unsi (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;
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