The following commit has been merged into the x86/urgent branch of tip: Commit-ID: c4bed4b96918ff1d062ee81fdae4d207da4fa9b0 Gitweb: https://git.kernel.org/tip/c4bed4b96918ff1d062ee81fdae4d207da4fa9b0 Author: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx> AuthorDate: Thu, 04 Feb 2021 23:27:06 +08:00 Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> CommitterDate: Fri, 05 Feb 2021 20:13:11 +01:00 x86/debug: Prevent data breakpoints on __per_cpu_offset When FSGSBASE is enabled, paranoid_entry() fetches the per-CPU GSBASE value via __per_cpu_offset or pcpu_unit_offsets. When a data breakpoint is set on __per_cpu_offset[cpu] (read-write operation), the specific CPU will be stuck in an infinite #DB loop. RCU will try to send an NMI to the specific CPU, but it is not working either since NMI also relies on paranoid_entry(). Which means it's undebuggable. Fixes: eaad981291ee3("x86/entry/64: Introduce the FIND_PERCPU_BASE macro") Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Link: https://lore.kernel.org/r/20210204152708.21308-1-jiangshanlai@xxxxxxxxx --- arch/x86/kernel/hw_breakpoint.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c index 6694c0f..012ed82 100644 --- a/arch/x86/kernel/hw_breakpoint.c +++ b/arch/x86/kernel/hw_breakpoint.c @@ -269,6 +269,20 @@ static inline bool within_cpu_entry(unsigned long addr, unsigned long end) CPU_ENTRY_AREA_TOTAL_SIZE)) return true; + /* + * When FSGSBASE is enabled, paranoid_entry() fetches the per-CPU + * GSBASE value via __per_cpu_offset or pcpu_unit_offsets. + */ +#ifdef CONFIG_SMP + if (within_area(addr, end, (unsigned long)__per_cpu_offset, + sizeof(unsigned long) * nr_cpu_ids)) + return true; +#else + if (within_area(addr, end, (unsigned long)&pcpu_unit_offsets, + sizeof(pcpu_unit_offsets))) + return true; +#endif + for_each_possible_cpu(cpu) { /* The original rw GDT is being used after load_direct_gdt() */ if (within_area(addr, end, (unsigned long)get_cpu_gdt_rw(cpu),
