linux-kernel - Re: [patch V3 1/2] x86/mm/pti: Handle unaligned address gracefully in pti_clone

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Date:   Thu, 29 Aug 2019 01:22:33 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Song Liu <songliubraving@...com>,
        Joerg Roedel <jroedel@...e.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Rik van Riel <riel@...riel.com>
Subject: Re: [patch V3 1/2] x86/mm/pti: Handle unaligned address gracefully
 in pti_clone_pagetable()


* Thomas Gleixner <tglx@...utronix.de> wrote:

> From: Song Liu <songliubraving@...com>
> 
> pti_clone_pmds() assumes that the supplied address is either:
> 
>  - properly PUD/PMD aligned
> or
>  - the address is actually mapped which means that independently
>    of the mapping level (PUD/PMD/PTE) the next higher mapping
>    exists.
> 
> If that's not the case the unaligned address can be incremented by PUD or
> PMD size incorrectly. All callers supply mapped and/or aligned addresses,
> but for the sake of robustness it's better to handle that case properly and
> to emit a warning.
> 
> [ tglx: Rewrote changelog and added WARN_ON_ONCE() ]
> 
> Signed-off-by: Song Liu <songliubraving@...com>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
> V2: Negate P[UM]D_MASK for checking whether the offset part is 0
> V3: Fix changelog
> ---
>  arch/x86/mm/pti.c |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> --- a/arch/x86/mm/pti.c
> +++ b/arch/x86/mm/pti.c
> @@ -330,13 +330,15 @@ pti_clone_pgtable(unsigned long start, u
>  
>  		pud = pud_offset(p4d, addr);
>  		if (pud_none(*pud)) {
> -			addr += PUD_SIZE;
> +			WARN_ON_ONCE(addr & ~PUD_MASK);
> +			addr = round_up(addr + 1, PUD_SIZE);
>  			continue;
>  		}
>  
>  		pmd = pmd_offset(pud, addr);
>  		if (pmd_none(*pmd)) {
> -			addr += PMD_SIZE;
> +			WARN_ON_ONCE(addr & ~PMD_MASK);
> +			addr = round_up(addr + 1, PMD_SIZE);
>  			continue;
>  		}

Reviewed-by: Ingo Molnar <mingo@...nel.org>

Thanks,

	Ingo