linux-kernel - Re: 1808d65b55 ("asm-generic/tlb: Remove arch_tlb*_mmu()"): BUG: KASAN: stack-out-of-bounds in __change_page_attr_set

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Message-ID: <CAHk-=wieBr3G=_ZGoCndi8XnuG1wtkedaGqkWB+=AVq65=_8sQ@mail.gmail.com>
Date:   Fri, 12 Apr 2019 08:32:38 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     kernel test robot <lkp@...el.com>, LKP <lkp@...org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will.deacon@....com>,
        Andy Lutomirski <luto@...nel.org>,
        Nadav Amit <namit@...are.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: 1808d65b55 ("asm-generic/tlb: Remove arch_tlb*_mmu()"): BUG:
 KASAN: stack-out-of-bounds in __change_page_attr_set_clr

On Fri, Apr 12, 2019 at 3:56 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> --- a/arch/x86/mm/tlb.c
> +++ b/arch/x86/mm/tlb.c
> @@ -728,7 +728,7 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
>  {
>         int cpu;
>
> -       struct flush_tlb_info info __aligned(SMP_CACHE_BYTES) = {
> +       struct flush_tlb_info info = {
>                 .mm = mm,
>                 .stride_shift = stride_shift,
>                 .freed_tables = freed_tables,
>

Ack.

We should never have stack alignment bigger than 16 bytes.  And
preferably not even that. Trying to align stack at a cacheline
boundary is wrong - if you *really* need things to be that aligned, do
something else (regular kmalloc, percpu temp area, static allocation -
whatever).

           Linus