diff options
author | Peter Zijlstra <peterz@infradead.org> | 2020-05-29 23:27:34 +0200 |
---|---|---|
committer | Thomas Gleixner <tglx@linutronix.de> | 2020-06-11 15:15:22 +0200 |
commit | fd338e3564b0b8597a89f83941a0eda3e5092cc0 (patch) | |
tree | 0e6b3615b536ef76b4d4e0eb0f2385967cee8cb2 /arch/x86/kernel/nmi.c | |
parent | e1de11d4d1a64ac1b90b9833f1a3629dae18facb (diff) | |
download | linux-stable-fd338e3564b0b8597a89f83941a0eda3e5092cc0.tar.gz linux-stable-fd338e3564b0b8597a89f83941a0eda3e5092cc0.tar.bz2 linux-stable-fd338e3564b0b8597a89f83941a0eda3e5092cc0.zip |
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) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200529213321.069223695@infradead.org
Diffstat (limited to 'arch/x86/kernel/nmi.c')
-rw-r--r-- | arch/x86/kernel/nmi.c | 55 |
1 files changed, 3 insertions, 52 deletions
diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c index 5df4e7f58369..873a8c040b86 100644 --- a/arch/x86/kernel/nmi.c +++ b/arch/x86/kernel/nmi.c @@ -474,40 +474,7 @@ 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) { @@ -522,18 +489,7 @@ 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(); @@ -544,12 +500,7 @@ 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)); |