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

Alexandre Chartre
2020-05-06T12:14:22Z

On 5/5/20 3:16 PM, Thomas Gleixner wrote:
> From: Andy Lutomirski <luto@kernel.org>
>
> A data breakpoint near the top of an IST stack will cause unresoverable

typo: unresoverable -> unrecoverable

> 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(+)

Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>

alex.

> --- 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;
>
>