On Thu, Jul 25, 2019 at 09:37:15AM -0700, Andy Lutomirski wrote: > A data breakpoint near the top of an IST stack will cause unresoverable > recursion. A data breakpoint on the GDT, IDT, or TSS is terrifying. > Prevent either of these from happening. > > Co-developed-by: Peter Zijlstra <[email protected]> > Signed-off-by: Andy Lutomirski <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]> One small nit beflow. > --- > > arch/x86/include/asm/cpu_entry_area.h | 10 ++++++++++ > arch/x86/kernel/hw_breakpoint.c | 17 +++++++++++++++++ > 2 files changed, 27 insertions(+) > > diff --git a/arch/x86/include/asm/cpu_entry_area.h > b/arch/x86/include/asm/cpu_entry_area.h > index e23e2d9a92d7..3f50d4738487 100644 > --- a/arch/x86/include/asm/cpu_entry_area.h > +++ b/arch/x86/include/asm/cpu_entry_area.h > @@ -126,6 +126,16 @@ static inline struct entry_stack *cpu_entry_stack(int > cpu) > return &get_cpu_entry_area(cpu)->entry_stack_page.stack; > } > > +/* > + * Checks whether the range from addr to end, inclusive, overlaps the CPU > + * entry area range. > + */ > +static inline bool within_cpu_entry_area(unsigned long addr, unsigned long > end) > +{ > + return end >= CPU_ENTRY_AREA_PER_CPU && > + addr < (CPU_ENTRY_AREA_PER_CPU + CPU_ENTRY_AREA_TOT_SIZE); > +} > + > #define __this_cpu_ist_top_va(name) \ > CEA_ESTACK_TOP(__this_cpu_read(cea_exception_stacks), name) > > diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c > index 218c8917118e..dc4581fe4b4e 100644 > --- a/arch/x86/kernel/hw_breakpoint.c > +++ b/arch/x86/kernel/hw_breakpoint.c > @@ -231,6 +231,23 @@ static int arch_build_bp_info(struct perf_event *bp, > const struct perf_event_attr *attr, > struct arch_hw_breakpoint *hw) > { > + unsigned long bp_end; > + > + /* Ensure that bp_end does not oveflow. */ > + if (attr->bp_len >= ULONG_MAX - attr->bp_addr) > + return -EINVAL; > + > + bp_end = attr->bp_addr + attr->bp_len - 1; The alternative (and possibly more conventional) overflow test would be: if (bp_end < attr->bp_addr) return -EINVAL; > + > + /* > + * Prevent any breakpoint of any type that overlaps the > + * cpu_entry_area. This protects the IST stacks and also > + * reduces the chance that we ever find out what happens if > + * there's a data breakpoint on the GDT, IDT, or TSS. > + */ > + if (within_cpu_entry_area(attr->bp_addr, bp_end)) > + return -EINVAL; > + > hw->address = attr->bp_addr; > hw->mask = 0; >
