diff options
Diffstat (limited to 'arch/x86/kernel/nmi.c')
| -rw-r--r-- | arch/x86/kernel/nmi.c | 102 |
1 files changed, 102 insertions, 0 deletions
diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c index e88f37b58dd..47acaf31916 100644 --- a/arch/x86/kernel/nmi.c +++ b/arch/x86/kernel/nmi.c @@ -405,9 +405,108 @@ static notrace __kprobes void default_do_nmi(struct pt_regs *regs) unknown_nmi_error(reason, regs); } +/* + * NMIs can hit breakpoints which will cause it to lose its + * NMI context with the CPU when the breakpoint does an iret. + */ +#ifdef CONFIG_X86_32 +/* + * For i386, NMIs use the same stack as the kernel, and we can + * add a workaround to the iret problem in C. Simply have 3 states + * the NMI can be in. + * + * 1) not running + * 2) executing + * 3) latched + * + * When no NMI is in progress, it is in the "not running" state. + * When an NMI comes in, it goes into the "executing" state. + * Normally, if another NMI is triggered, it does not interrupt + * the running NMI and the HW will simply latch it so that when + * the first NMI finishes, it will restart the second NMI. + * (Note, the latch is binary, thus multiple NMIs triggering, + * when one is running, are ignored. Only one NMI is restarted.) + * + * If an NMI hits a breakpoint that executes an iret, another + * NMI can preempt it. We do not want to allow this new NMI + * to run, but we want to execute it when the first one finishes. + * We set the state to "latched", and the first NMI will perform + * an cmpxchg on the state, and if it doesn't successfully + * reset the state to "not running" it will restart the next + * NMI. + */ +enum nmi_states { + NMI_NOT_RUNNING, + NMI_EXECUTING, + NMI_LATCHED, +}; +static DEFINE_PER_CPU(enum nmi_states, nmi_state); + +#define nmi_nesting_preprocess(regs) \ + do { \ + if (__get_cpu_var(nmi_state) != NMI_NOT_RUNNING) { \ + __get_cpu_var(nmi_state) = NMI_LATCHED; \ + return; \ + } \ + nmi_restart: \ + __get_cpu_var(nmi_state) = NMI_EXECUTING; \ + } while (0) + +#define nmi_nesting_postprocess() \ + do { \ + if (cmpxchg(&__get_cpu_var(nmi_state), \ + NMI_EXECUTING, NMI_NOT_RUNNING) != NMI_EXECUTING) \ + goto nmi_restart; \ + } while (0) +#else /* x86_64 */ +/* + * In x86_64 things are a bit more difficult. This has the same problem + * where an NMI hitting a breakpoint that calls iret will remove the + * NMI context, allowing a nested NMI to enter. What makes this more + * difficult is that both NMIs and breakpoints have their own stack. + * When a new NMI or breakpoint is executed, the stack is set to a fixed + * point. If an NMI is nested, it will have its stack set at that same + * fixed address that the first NMI had, and will start corrupting the + * stack. This is handled in entry_64.S, but the same problem exists with + * the breakpoint 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 inline void nmi_nesting_preprocess(struct pt_regs *regs) +{ + /* + * 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(); + __get_cpu_var(update_debug_stack) = 1; + } +} + +static inline void nmi_nesting_postprocess(void) +{ + if (unlikely(__get_cpu_var(update_debug_stack))) + debug_stack_reset(); +} +#endif + dotraplinkage notrace __kprobes void do_nmi(struct pt_regs *regs, long error_code) { + nmi_nesting_preprocess(regs); + nmi_enter(); inc_irq_stat(__nmi_count); @@ -416,6 +515,9 @@ do_nmi(struct pt_regs *regs, long error_code) default_do_nmi(regs); nmi_exit(); + + /* On i386, may loop back to preprocess */ + nmi_nesting_postprocess(); } void stop_nmi(void) |