leandrof/linux
1
0
Fork 0
forked from Minki/linux
Code Issues Pull Requests Packages Projects Releases Wiki Activity

x86/entry, nmi: Disable #DB

Browse Source 
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
This commit is contained in:
Peter Zijlstra 2020-05-29 23:27:34 +02:00 committed by Thomas Gleixner
parent e1de11d4d1
commit fd338e3564
1 changed files with 3 additions and 52 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

55
arch/x86/kernel/nmi.c
View File

@ -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));