linux-kernel - Re: [PATCH 2/2] sparc: Check VMA range in sparc_validate

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Date:   Wed, 7 Oct 2020 14:15:28 -0600
From:   Khalid Aziz <khalid.aziz@...cle.com>
To:     Jann Horn <jannh@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        sparclinux@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org,
        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
Subject: Re: [PATCH 2/2] sparc: Check VMA range in sparc_validate_prot()

On 10/7/20 1:39 AM, Jann Horn wrote:
> sparc_validate_prot() is called from do_mprotect_pkey() as
> arch_validate_prot(); it tries to ensure that an mprotect() call can't
> enable ADI on incompatible VMAs.
> The current implementation only checks that the VMA at the start address
> matches the rules for ADI mappings; instead, check all VMAs that will be
> affected by mprotect().
> 
> (This hook is called before mprotect() makes sure that the specified range
> is actually covered by VMAs, and mprotect() returns specific error codes
> when that's not the case. In order for mprotect() to still generate the
> same error codes for mprotect(<unmapped_ptr>, <len>, ...|PROT_ADI), we need
> to *accept* cases where the range is not fully covered by VMAs.)
> 
> Cc: stable@...r.kernel.org
> Fixes: 74a04967482f ("sparc64: Add support for ADI (Application Data Integrity)")
> Signed-off-by: Jann Horn <jannh@...gle.com>
> ---
> compile-tested only, I don't have a Sparc ADI setup - might be nice if some
> Sparc person could test this?
> 
>  arch/sparc/include/asm/mman.h | 50 +++++++++++++++++++++--------------
>  1 file changed, 30 insertions(+), 20 deletions(-)


Looks good to me.

Reviewed-by: Khalid Aziz <khalid.aziz@...cle.com>


> 
> diff --git a/arch/sparc/include/asm/mman.h b/arch/sparc/include/asm/mman.h
> index e85222c76585..6dced75567c3 100644
> --- a/arch/sparc/include/asm/mman.h
> +++ b/arch/sparc/include/asm/mman.h
> @@ -60,31 +60,41 @@ static inline int sparc_validate_prot(unsigned long prot, unsigned long addr,
>  	if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM | PROT_ADI))
>  		return 0;
>  	if (prot & PROT_ADI) {
> +		struct vm_area_struct *vma, *next;
> +
>  		if (!adi_capable())
>  			return 0;
>  
> -		if (addr) {
> -			struct vm_area_struct *vma;
> +		vma = find_vma(current->mm, addr);
> +		/* if @addr is unmapped, let mprotect() deal with it */
> +		if (!vma || vma->vm_start > addr)
> +			return 1;
> +		while (1) {
> +			/* ADI can not be enabled on PFN
> +			 * mapped pages
> +			 */
> +			if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
> +				return 0;
>  
> -			vma = find_vma(current->mm, addr);
> -			if (vma) {
> -				/* ADI can not be enabled on PFN
> -				 * mapped pages
> -				 */
> -				if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
> -					return 0;
> +			/* Mergeable pages can become unmergeable
> +			 * if ADI is enabled on them even if they
> +			 * have identical data on them. This can be
> +			 * because ADI enabled pages with identical
> +			 * data may still not have identical ADI
> +			 * tags on them. Disallow ADI on mergeable
> +			 * pages.
> +			 */
> +			if (vma->vm_flags & VM_MERGEABLE)
> +				return 0;
>  
> -				/* Mergeable pages can become unmergeable
> -				 * if ADI is enabled on them even if they
> -				 * have identical data on them. This can be
> -				 * because ADI enabled pages with identical
> -				 * data may still not have identical ADI
> -				 * tags on them. Disallow ADI on mergeable
> -				 * pages.
> -				 */
> -				if (vma->vm_flags & VM_MERGEABLE)
> -					return 0;
> -			}
> +			/* reached the end of the range without errors? */
> +			if (addr+len <= vma->vm_end)
> +				return 1;
> +			next = vma->vm_next;
> +			/* if a VMA hole follows, let mprotect() deal with it */
> +			if (!next || next->vm_start != vma->vm_end)
> +				return 1;
> +			vma = next;
>  		}
>  	}
>  	return 1;
>