Re: [PATCH 18/28] mm: enforce that vmap can't map pages executable

From: Mark Rutland <mark.rutland@arm.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	"K. Y. Srinivasan" <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	Wei Liu <wei.liu@kernel.org>,
	x86@kernel.org, David Airlie <airlied@linux.ie>,
	Daniel Vetter <daniel@ffwll.ch>,
	Laura Abbott <labbott@redhat.com>,
	Sumit Semwal <sumit.semwal@linaro.org>,
	Sakari Ailus <sakari.ailus@linux.intel.com>,
	Minchan Kim <minchan@kernel.org>, Nitin Gupta <ngupta@vflare.org>,
	Robin Murphy <robin.murphy@arm.com>,
	Christophe Leroy <christophe.leroy@c-s.fr>,
	Peter Zijlstra <peterz@infradead.org>,
	linuxppc-dev@lists.ozlabs.org, linux-hyperv@vger.kernel.org,
	dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org,
	linux-arch@vger.kernel.org, linux-mm@kvack.org,
	iommu@lists.linux-foundation.org,
	linux-arm-kernel@lists.infradead.org, linux-s390@vger.kernel.org,
	bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
	Will Deacon <will@kernel.org>,
	Catalin marinas <catalin.marinas@arm.com>
Subject: Re: [PATCH 18/28] mm: enforce that vmap can't map pages executable
Date: Wed, 8 Apr 2020 13:38:36 +0100	[thread overview]
Message-ID: <20200408123835.GB36478@lakrids.cambridge.arm.com> (raw)
In-Reply-To: <20200408115926.1467567-19-hch@lst.de>

On Wed, Apr 08, 2020 at 01:59:16PM +0200, Christoph Hellwig wrote:
> To help enforcing the W^X protection don't allow remapping existing
> pages as executable.
> 
> Based on patch from Peter Zijlstra <peterz@infradead.org>.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  arch/x86/include/asm/pgtable_types.h | 6 ++++++
>  include/asm-generic/pgtable.h        | 4 ++++
>  mm/vmalloc.c                         | 2 +-
>  3 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
> index 947867f112ea..2e7c442cc618 100644
> --- a/arch/x86/include/asm/pgtable_types.h
> +++ b/arch/x86/include/asm/pgtable_types.h
> @@ -282,6 +282,12 @@ typedef struct pgprot { pgprotval_t pgprot; } pgprot_t;
>  
>  typedef struct { pgdval_t pgd; } pgd_t;
>  
> +static inline pgprot_t pgprot_nx(pgprot_t prot)
> +{
> +	return __pgprot(pgprot_val(prot) | _PAGE_NX);
> +}
> +#define pgprot_nx pgprot_nx
> +
>  #ifdef CONFIG_X86_PAE

I reckon for arm64 we can do similar in our <asm/pgtable.h>:

#define pgprot_nx(pgprot_t prot) \
	__pgprot_modify(prot, 0, PTE_PXN)

... matching the style of our existing pgprot_*() modifier helpers.

Mark.

>  
>  /*
> diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
> index 329b8c8ca703..8c5f9c29698b 100644
> --- a/include/asm-generic/pgtable.h
> +++ b/include/asm-generic/pgtable.h
> @@ -491,6 +491,10 @@ static inline int arch_unmap_one(struct mm_struct *mm,
>  #define flush_tlb_fix_spurious_fault(vma, address) flush_tlb_page(vma, address)
>  #endif
>  
> +#ifndef pgprot_nx
> +#define pgprot_nx(prot)	(prot)
> +#endif
> +
>  #ifndef pgprot_noncached
>  #define pgprot_noncached(prot)	(prot)
>  #endif
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 7356b3f07bd8..334c75251ddb 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2390,7 +2390,7 @@ void *vmap(struct page **pages, unsigned int count,
>  	if (!area)
>  		return NULL;
>  
> -	if (map_kernel_range((unsigned long)area->addr, size, prot,
> +	if (map_kernel_range((unsigned long)area->addr, size, pgprot_nx(prot),
>  			pages) < 0) {
>  		vunmap(area->addr);
>  		return NULL;
> -- 
> 2.25.1
> 