linux-kernel - Re: [PATCH 1/2] mm/mprotect: Call arch_validate_prot under mmap

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Message-ID: <20201007123544.GA11433@infradead.org>
Date:   Wed, 7 Oct 2020 13:35:44 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Jann Horn <jannh@...gle.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        sparclinux@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Khalid Aziz <khalid.aziz@...cle.com>,
        Christoph Hellwig <hch@...radead.org>,
        Anthony Yznaga <anthony.yznaga@...cle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org,
        Dave Kleikamp <shaggy@...ux.vnet.ibm.com>
Subject: Re: [PATCH 1/2] mm/mprotect: Call arch_validate_prot under mmap_lock
 and with length

On Wed, Oct 07, 2020 at 09:39:31AM +0200, Jann Horn wrote:
> diff --git a/arch/powerpc/kernel/syscalls.c b/arch/powerpc/kernel/syscalls.c
> index 078608ec2e92..b1fabb97d138 100644
> --- a/arch/powerpc/kernel/syscalls.c
> +++ b/arch/powerpc/kernel/syscalls.c
> @@ -43,7 +43,7 @@ static inline long do_mmap2(unsigned long addr, size_t len,
>  {
>  	long ret = -EINVAL;
>  
> -	if (!arch_validate_prot(prot, addr))
> +	if (!arch_validate_prot(prot, addr, len))

This call isn't under mmap lock.  I also find it rather weird as the
generic code only calls arch_validate_prot from mprotect, only powerpc
also calls it from mmap.

This seems to go back to commit ef3d3246a0d0
("powerpc/mm: Add Strong Access Ordering support")