diff options
| -rw-r--r-- | arch/x86/entry/entry_64.S | 36 | ||||
| -rw-r--r-- | arch/x86/kernel/traps.c | 4 |
2 files changed, 40 insertions, 0 deletions
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 957dfb693ecc..ce6af4460e9c 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -900,6 +900,42 @@ apicinterrupt IRQ_WORK_VECTOR irq_work_interrupt smp_irq_work_interrupt */ #define CPU_TSS_IST(x) PER_CPU_VAR(cpu_tss_rw) + (TSS_ist + ((x) - 1) * 8) +/** + * idtentry - Generate an IDT entry stub + * @sym: Name of the generated entry point + * @do_sym: C function to be called + * @has_error_code: True if this IDT vector has an error code on the stack + * @paranoid: non-zero means that this vector may be invoked from + * kernel mode with user GSBASE and/or user CR3. + * 2 is special -- see below. + * @shift_ist: Set to an IST index if entries from kernel mode should + * decrement the IST stack so that nested entries get a + * fresh stack. (This is for #DB, which has a nasty habit + * of recursing.) + * + * idtentry generates an IDT stub that sets up a usable kernel context, + * creates struct pt_regs, and calls @do_sym. The stub has the following + * special behaviors: + * + * On an entry from user mode, the stub switches from the trampoline or + * IST stack to the normal thread stack. On an exit to user mode, the + * normal exit-to-usermode path is invoked. + * + * On an exit to kernel mode, if @paranoid == 0, we check for preemption, + * whereas we omit the preemption check if @paranoid != 0. This is purely + * because the implementation is simpler this way. The kernel only needs + * to check for asynchronous kernel preemption when IRQ handlers return. + * + * If @paranoid == 0, then the stub will handle IRET faults by pretending + * that the fault came from user mode. It will handle gs_change faults by + * pretending that the fault happened with kernel GSBASE. Since this handling + * is omitted for @paranoid != 0, the #GP, #SS, and #NP stubs must have + * @paranoid == 0. This special handling will do the wrong thing for + * espfix-induced #DF on IRET, so #DF must not use @paranoid == 0. + * + * @paranoid == 2 is special: the stub will never switch stacks. This is for + * #DF: if the thread stack is somehow unusable, we'll still get a useful OOPS. + */ .macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1 ENTRY(\sym) UNWIND_HINT_IRET_REGS offset=\has_error_code*8 diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index e6db475164ed..1a90821c0b74 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -383,6 +383,10 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code) * we won't enable interupts or schedule before we invoke * general_protection, so nothing will clobber the stack * frame we just set up. + * + * We will enter general_protection with kernel GSBASE, + * which is what the stub expects, given that the faulting + * RIP will be the IRET instruction. */ regs->ip = (unsigned long)general_protection; regs->sp = (unsigned long)&gpregs->orig_ax; |