linux-kernel - Re: [patch V4 part 1 02/36] x86/hw_breakpoint: Prevent data breakpoints on cpu_entry

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Date:   Wed, 6 May 2020 14:11:45 +0200
From:   Alexandre Chartre <alexandre.chartre@...cle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [patch V4 part 1 02/36] x86/hw_breakpoint: Prevent data
 breakpoints on cpu_entry_area


On 5/5/20 3:16 PM, Thomas Gleixner wrote:
> From: Andy Lutomirski <luto@...nel.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@...radead.org>
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>   arch/x86/kernel/hw_breakpoint.c |   25 +++++++++++++++++++++++++
>   1 file changed, 25 insertions(+)

Reviewed-by: Alexandre Chartre <alexandre.chartre@...cle.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;
>   
>