[patch V4 part 1 02/36] x86/hw_breakpoint: Prevent data breakpoints on cpu_entry_area

Thomas Gleixner
2020-05-05T14:24:21Z

From: Andy Lutomirski <luto@kernel.org>

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 <peterz@infradead.org>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/kernel/hw_breakpoint.c | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)

--- a/arch/x86/kernel/hw_breakpoint.c
+++ b/arch/x86/kernel/hw_breakpoint.c
@@ -227,10 +227,35 @@ int arch_check_bp_in_kernelspace(struct
return (va >= TASK_SIZE_MAX) || ((va + len - 1) >= TASK_SIZE_MAX);
}

+/*
+ * 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_TOTAL_SIZE);
+}
+
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;
+
+ bp_end = attr->bp_addr + attr->bp_len - 1;
+ 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;