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x86/doublefault/32: Move #DF stack and TSS to cpu_entry_area

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There are three problems with the current layout of the doublefault
stack and TSS.  First, the TSS is only cacheline-aligned, which is
not enough -- if the hardware portion of the TSS (struct x86_hw_tss)
crosses a page boundary, horrible things happen [0].  Second, the
stack and TSS are global, so simultaneous double faults on different
CPUs will cause massive corruption.  Third, the whole mechanism
won't work if user CR3 is loaded, resulting in a triple fault [1].

Let the doublefault stack and TSS share a page (which prevents the
TSS from spanning a page boundary), make it percpu, and move it into
cpu_entry_area.  Teach the stack dump code about the doublefault
stack.

[0] Real hardware will read past the end of the page onto the next
    *physical* page if a task switch happens.  Virtual machines may
    have any number of bugs, and I would consider it reasonable for
    a VM to summarily kill the guest if it tries to task-switch to
    a page-spanning TSS.

[1] Real hardware triple faults.  At least some VMs seem to hang.
    I'm not sure what's going on.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski
2019-11-26 18:27:16 +01:00
committed by Ingo Molnar
parent e99b6f46ee
commit dc4e0021b0
8 changed files with 113 additions and 34 deletions
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30
arch/x86/kernel/dumpstack_32.c
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@@ -29,6 +29,9 @@ const char *stack_type_name(enum stack_type type)
if (type == STACK_TYPE_ENTRY)
return "ENTRY_TRAMPOLINE";
if (type == STACK_TYPE_EXCEPTION)
return "#DF";
return NULL;
}
@@ -82,6 +85,30 @@ static bool in_softirq_stack(unsigned long *stack, struct stack_info *info)
return true;
}
static bool in_doublefault_stack(unsigned long *stack, struct stack_info *info)
{
#ifdef CONFIG_DOUBLEFAULT
struct cpu_entry_area *cea = get_cpu_entry_area(raw_smp_processor_id());
struct doublefault_stack *ss = &cea->doublefault_stack;
void *begin = ss->stack;
void *end = begin + sizeof(ss->stack);
if ((void *)stack < begin || (void *)stack >= end)
return false;
info->type = STACK_TYPE_EXCEPTION;
info->begin = begin;
info->end = end;
info->next_sp = (unsigned long *)this_cpu_read(cpu_tss_rw.x86_tss.sp);
return true;
#else
return false;
#endif
}
int get_stack_info(unsigned long *stack, struct task_struct *task,
struct stack_info *info, unsigned long *visit_mask)
{
@@ -105,6 +132,9 @@ int get_stack_info(unsigned long *stack, struct task_struct *task,
if (in_softirq_stack(stack, info))
goto recursion_check;
if (in_doublefault_stack(stack, info))
goto recursion_check;
goto unknown;
recursion_check: