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]> --- The rest of my series is still in progress -- as we all know, idtentry is a morass. But this is self-contained and is an obvious fix. 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; + + /* + * 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; -- 2.21.0
