linux-kernel - Re: [PATCH V3 1/2] mm/mmap: Restrict generic protection

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Message-ID: <4830e415-cdbb-7050-ebd6-7480493655ef@csgroup.eu>
Date:   Thu, 16 Jun 2022 05:35:36 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Anshuman Khandual <anshuman.khandual@....com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
CC:     "hch@...radead.org" <hch@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH V3 1/2] mm/mmap: Restrict generic protection_map[] array
 visibility



Le 16/06/2022 à 06:09, Anshuman Khandual a écrit :
> Restrict generic protection_map[] array visibility only for platforms which
> do not enable ARCH_HAS_VM_GET_PAGE_PROT. For other platforms that do define
> their own vm_get_page_prot() enabling ARCH_HAS_VM_GET_PAGE_PROT, could have
> their private static protection_map[] still implementing an array look up.
> These private protection_map[] array could do without __PXXX/__SXXX macros,
> making them redundant and dropping them off as well.
> 
> But platforms which do not define their custom vm_get_page_prot() enabling
> ARCH_HAS_VM_GET_PAGE_PROT, will still have to provide __PXXX/__SXXX macros.
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> Acked-by: Christoph Hellwig <hch@....de>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
>   arch/arm64/include/asm/pgtable-prot.h | 18 ------------------
>   arch/arm64/mm/mmap.c                  | 21 +++++++++++++++++++++
>   arch/powerpc/include/asm/pgtable.h    |  2 ++
>   arch/powerpc/mm/book3s64/pgtable.c    | 20 ++++++++++++++++++++
>   arch/sparc/include/asm/pgtable_64.h   | 19 -------------------
>   arch/sparc/mm/init_64.c               |  3 +++
>   arch/x86/include/asm/pgtable_types.h  | 19 -------------------
>   arch/x86/mm/pgprot.c                  | 19 +++++++++++++++++++
>   include/linux/mm.h                    |  2 ++
>   mm/mmap.c                             |  2 +-
>   10 files changed, 68 insertions(+), 57 deletions(-)
> 

> diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
> index d564d0ecd4cd..8ed2a80c896e 100644
> --- a/arch/powerpc/include/asm/pgtable.h
> +++ b/arch/powerpc/include/asm/pgtable.h
> @@ -21,6 +21,7 @@ struct mm_struct;
>   #endif /* !CONFIG_PPC_BOOK3S */
>   
>   /* Note due to the way vm flags are laid out, the bits are XWR */
> +#ifndef CONFIG_ARCH_HAS_VM_GET_PAGE_PROT

This ifdef if not necessary for now, it doesn't matter if __P000 etc 
still exist thought not used.

>   #define __P000	PAGE_NONE
>   #define __P001	PAGE_READONLY
>   #define __P010	PAGE_COPY
> @@ -38,6 +39,7 @@ struct mm_struct;
>   #define __S101	PAGE_READONLY_X
>   #define __S110	PAGE_SHARED_X
>   #define __S111	PAGE_SHARED_X
> +#endif
>   
>   #ifndef __ASSEMBLY__
>   
> diff --git a/arch/powerpc/mm/book3s64/pgtable.c b/arch/powerpc/mm/book3s64/pgtable.c
> index 7b9966402b25..d3b019b95c1d 100644
> --- a/arch/powerpc/mm/book3s64/pgtable.c
> +++ b/arch/powerpc/mm/book3s64/pgtable.c
> @@ -551,6 +551,26 @@ unsigned long memremap_compat_align(void)
>   EXPORT_SYMBOL_GPL(memremap_compat_align);
>   #endif
>   
> +/* Note due to the way vm flags are laid out, the bits are XWR */
> +static const pgprot_t protection_map[16] = {
> +	[VM_NONE]					= PAGE_NONE,
> +	[VM_READ]					= PAGE_READONLY,
> +	[VM_WRITE]					= PAGE_COPY,
> +	[VM_WRITE | VM_READ]				= PAGE_COPY,
> +	[VM_EXEC]					= PAGE_READONLY_X,
> +	[VM_EXEC | VM_READ]				= PAGE_READONLY_X,
> +	[VM_EXEC | VM_WRITE]				= PAGE_COPY_X,
> +	[VM_EXEC | VM_WRITE | VM_READ]			= PAGE_COPY_X,
> +	[VM_SHARED]					= PAGE_NONE,
> +	[VM_SHARED | VM_READ]				= PAGE_READONLY,
> +	[VM_SHARED | VM_WRITE]				= PAGE_SHARED,
> +	[VM_SHARED | VM_WRITE | VM_READ]		= PAGE_SHARED,
> +	[VM_SHARED | VM_EXEC]				= PAGE_READONLY_X,
> +	[VM_SHARED | VM_EXEC | VM_READ]			= PAGE_READONLY_X,
> +	[VM_SHARED | VM_EXEC | VM_WRITE]		= PAGE_SHARED_X,
> +	[VM_SHARED | VM_EXEC | VM_WRITE | VM_READ]	= PAGE_SHARED_X
> +};
> +

There is not much point is first additing that here and then move it 
elsewhere in the second patch.

I think with my suggestion to use #ifdef __P000 as a guard, the powerpc 
changes could go in a single patch.

>   pgprot_t vm_get_page_prot(unsigned long vm_flags)
>   {
>   	unsigned long prot = pgprot_val(protection_map[vm_flags &
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 61e6135c54ef..e66920414945 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -101,6 +101,7 @@ static void unmap_region(struct mm_struct *mm,
>    *								w: (no) no
>    *								x: (yes) yes
>    */
> +#ifndef CONFIG_ARCH_HAS_VM_GET_PAGE_PROT

You should use #ifdef __P000 instead, that way you could migrate 
architectures one by one.

>   pgprot_t protection_map[16] __ro_after_init = {
>   	[VM_NONE]					= __P000,
>   	[VM_READ]					= __P001,
> @@ -120,7 +121,6 @@ pgprot_t protection_map[16] __ro_after_init = {
>   	[VM_SHARED | VM_EXEC | VM_WRITE | VM_READ]	= __S111
>   };
>   
> -#ifndef CONFIG_ARCH_HAS_VM_GET_PAGE_PROT
>   pgprot_t vm_get_page_prot(unsigned long vm_flags)
>   {
>   	return protection_map[vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)];