The following commit has been merged into the x86/entry branch of tip: Commit-ID: af87e4c4d65b2008709efcfb7657551f1c62a98b Gitweb: https://git.kernel.org/tip/af87e4c4d65b2008709efcfb7657551f1c62a98b Author: Peter Zijlstra <pet...@infradead.org> AuthorDate: Fri, 29 May 2020 23:27:34 +02:00 Committer: Thomas Gleixner <t...@linutronix.de> CommitterDate: Sat, 30 May 2020 10:00:07 +02:00
x86/entry, nmi: Disable #DB Instead of playing stupid games with IST stacks, fully disallow #DB during NMIs. There is absolutely no reason to allow them, and killing this saves a heap of trouble. #DB is already forbidden on noinstr and CEA, so there can't be a #DB before this. Disabling it right after nmi_enter() ensures that the full NMI code is protected. Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Signed-off-by: Thomas Gleixner <t...@linutronix.de> Link: https://lkml.kernel.org/r/20200529213321.069223...@infradead.org --- arch/x86/kernel/nmi.c | 55 ++---------------------------------------- 1 file changed, 3 insertions(+), 52 deletions(-) diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c index 1c58454..52a708e 100644 --- a/arch/x86/kernel/nmi.c +++ b/arch/x86/kernel/nmi.c @@ -478,40 +478,7 @@ enum nmi_states { }; static DEFINE_PER_CPU(enum nmi_states, nmi_state); static DEFINE_PER_CPU(unsigned long, nmi_cr2); - -#ifdef CONFIG_X86_64 -/* - * In x86_64, we need to handle breakpoint -> NMI -> breakpoint. Without - * some care, the inner breakpoint will clobber the outer breakpoint's - * stack. - * - * If a breakpoint is being processed, and the debug stack is being - * used, if an NMI comes in and also hits a breakpoint, the stack - * pointer will be set to the same fixed address as the breakpoint that - * was interrupted, causing that stack to be corrupted. To handle this - * case, check if the stack that was interrupted is the debug stack, and - * if so, change the IDT so that new breakpoints will use the current - * stack and not switch to the fixed address. On return of the NMI, - * switch back to the original IDT. - */ -static DEFINE_PER_CPU(int, update_debug_stack); - -static noinstr bool is_debug_stack(unsigned long addr) -{ - struct cea_exception_stacks *cs = __this_cpu_read(cea_exception_stacks); - unsigned long top = CEA_ESTACK_TOP(cs, DB); - unsigned long bot = CEA_ESTACK_BOT(cs, DB1); - - if (__this_cpu_read(debug_stack_usage)) - return true; - /* - * Note, this covers the guard page between DB and DB1 as well to - * avoid two checks. But by all means @addr can never point into - * the guard page. - */ - return addr >= bot && addr < top; -} -#endif +static DEFINE_PER_CPU(unsigned long, nmi_dr7); DEFINE_IDTENTRY_NMI(exc_nmi) { @@ -526,18 +493,7 @@ DEFINE_IDTENTRY_NMI(exc_nmi) this_cpu_write(nmi_cr2, read_cr2()); nmi_restart: -#ifdef CONFIG_X86_64 - /* - * If we interrupted a breakpoint, it is possible that - * the nmi handler will have breakpoints too. We need to - * change the IDT such that breakpoints that happen here - * continue to use the NMI stack. - */ - if (unlikely(is_debug_stack(regs->sp))) { - debug_stack_set_zero(); - this_cpu_write(update_debug_stack, 1); - } -#endif + this_cpu_write(nmi_dr7, local_db_save()); nmi_enter(); @@ -548,12 +504,7 @@ nmi_restart: nmi_exit(); -#ifdef CONFIG_X86_64 - if (unlikely(this_cpu_read(update_debug_stack))) { - debug_stack_reset(); - this_cpu_write(update_debug_stack, 0); - } -#endif + local_db_restore(this_cpu_read(nmi_dr7)); if (unlikely(this_cpu_read(nmi_cr2) != read_cr2())) write_cr2(this_cpu_read(nmi_cr2));
