diff options
Diffstat (limited to 'drivers/misc/lkdtm/bugs.c')
| -rw-r--r-- | drivers/misc/lkdtm/bugs.c | 39 |
1 files changed, 39 insertions, 0 deletions
diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c index 7284a22b1a09..a4fdad04809a 100644 --- a/drivers/misc/lkdtm/bugs.c +++ b/drivers/misc/lkdtm/bugs.c @@ -12,6 +12,10 @@ #include <linux/sched/task_stack.h> #include <linux/uaccess.h> +#ifdef CONFIG_X86_32 +#include <asm/desc.h> +#endif + struct lkdtm_list { struct list_head node; }; @@ -337,3 +341,38 @@ void lkdtm_UNSET_SMEP(void) pr_err("FAIL: this test is x86_64-only\n"); #endif } + +#ifdef CONFIG_X86_32 +void lkdtm_DOUBLE_FAULT(void) +{ + /* + * Trigger #DF by setting the stack limit to zero. This clobbers + * a GDT TLS slot, which is okay because the current task will die + * anyway due to the double fault. + */ + struct desc_struct d = { + .type = 3, /* expand-up, writable, accessed data */ + .p = 1, /* present */ + .d = 1, /* 32-bit */ + .g = 0, /* limit in bytes */ + .s = 1, /* not system */ + }; + + local_irq_disable(); + write_gdt_entry(get_cpu_gdt_rw(smp_processor_id()), + GDT_ENTRY_TLS_MIN, &d, DESCTYPE_S); + + /* + * Put our zero-limit segment in SS and then trigger a fault. The + * 4-byte access to (%esp) will fault with #SS, and the attempt to + * deliver the fault will recursively cause #SS and result in #DF. + * This whole process happens while NMIs and MCEs are blocked by the + * MOV SS window. This is nice because an NMI with an invalid SS + * would also double-fault, resulting in the NMI or MCE being lost. + */ + asm volatile ("movw %0, %%ss; addl $0, (%%esp)" :: + "r" ((unsigned short)(GDT_ENTRY_TLS_MIN << 3))); + + panic("tried to double fault but didn't die\n"); +} +#endif |