Re: [PATCH 1/6] mm/mmap: Restrict generic protection_map[] array visibility

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 03/06/2022 à 12:14, 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.
> 
> 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.
> Although this now provides a method for other willing platforms to drop off
> __PXXX/__SXX macros completely.
> 
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: x86@kernel.org
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linuxppc-dev@lists.ozlabs.org
> Cc: sparclinux@vger.kernel.org
> Cc: linux-mm@kvack.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.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_32.h   |  2 ++
>   arch/sparc/include/asm/pgtable_64.h   | 19 -------------------
>   arch/sparc/mm/init_64.c               | 20 ++++++++++++++++++++
>   arch/x86/include/asm/pgtable_types.h  | 19 -------------------
>   arch/x86/mm/pgprot.c                  | 19 +++++++++++++++++++
>   include/linux/mm.h                    |  2 ++
>   mm/mmap.c                             |  2 +-
>   11 files changed, 87 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

Ok, so until now it was common to all powerpc platforms. Now you define 
a different way whether it is a PPC_BOOK3S_64 or another platform ? 
What's the point ?

>   #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..2cf10a17c0a9 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 pgprot_t protection_map[16] __ro_after_init = {

I don't think powerpc modifies that at all. Could be const instead of 
ro_after_init.

> +	[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
> +};

That's nice but it could apply to all powerpc platforms. Why restrict it 
to book3s/64 ?

> +
>   pgprot_t vm_get_page_prot(unsigned long vm_flags)
>   {
>   	unsigned long prot = pgprot_val(protection_map[vm_flags &
> diff --git a/arch/sparc/include/asm/pgtable_32.h b/arch/sparc/include/asm/pgtable_32.h
> index 4866625da314..bca98b280fdd 100644
> --- a/arch/sparc/include/asm/pgtable_32.h
> +++ b/arch/sparc/include/asm/pgtable_32.h
> @@ -65,6 +65,7 @@ void paging_init(void);
>   extern unsigned long ptr_in_current_pgd;
>   
>   /*         xwr */
> +#ifndef CONFIG_ARCH_HAS_VM_GET_PAGE_PROT

CONFIG_ARCH_HAS_VM_GET_PAGE_PROT is selected by sparc64 only, is that 
ifdef needed at all ?

>   #define __P000  PAGE_NONE
>   #define __P001  PAGE_READONLY
>   #define __P010  PAGE_COPY
> @@ -82,6 +83,7 @@ extern unsigned long ptr_in_current_pgd;
>   #define __S101	PAGE_READONLY
>   #define __S110	PAGE_SHARED
>   #define __S111	PAGE_SHARED
> +#endif
>   
>   /* First physical page can be anywhere, the following is needed so that
>    * va-->pa and vice versa conversions work properly without performance
> diff --git a/arch/sparc/include/asm/pgtable_64.h b/arch/sparc/include/asm/pgtable_64.h
> index 4679e45c8348..a779418ceba9 100644
> --- a/arch/sparc/include/asm/pgtable_64.h
> +++ b/arch/sparc/include/asm/pgtable_64.h
> @@ -187,25 +187,6 @@ bool kern_addr_valid(unsigned long addr);
>   #define _PAGE_SZHUGE_4U	_PAGE_SZ4MB_4U
>   #define _PAGE_SZHUGE_4V	_PAGE_SZ4MB_4V
>   
> -/* These are actually filled in at boot time by sun4{u,v}_pgprot_init() */
> -#define __P000	__pgprot(0)
> -#define __P001	__pgprot(0)
> -#define __P010	__pgprot(0)
> -#define __P011	__pgprot(0)
> -#define __P100	__pgprot(0)
> -#define __P101	__pgprot(0)
> -#define __P110	__pgprot(0)
> -#define __P111	__pgprot(0)
> -
> -#define __S000	__pgprot(0)
> -#define __S001	__pgprot(0)
> -#define __S010	__pgprot(0)
> -#define __S011	__pgprot(0)
> -#define __S100	__pgprot(0)
> -#define __S101	__pgprot(0)
> -#define __S110	__pgprot(0)
> -#define __S111	__pgprot(0)
> -
>   #ifndef __ASSEMBLY__
>   
>   pte_t mk_pte_io(unsigned long, pgprot_t, int, unsigned long);
> diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c
> index f6174df2d5af..6edc2a68b73c 100644
> --- a/arch/sparc/mm/init_64.c
> +++ b/arch/sparc/mm/init_64.c
> @@ -2634,6 +2634,26 @@ void vmemmap_free(unsigned long start, unsigned long end,
>   }
>   #endif /* CONFIG_SPARSEMEM_VMEMMAP */
>   
> +/* These are actually filled in at boot time by sun4{u,v}_pgprot_init() */
> +static pgprot_t protection_map[16] __ro_after_init = {
> +	[VM_NONE]					= __pgprot(0),
> +	[VM_READ]					= __pgprot(0),
> +	[VM_WRITE]					= __pgprot(0),
> +	[VM_WRITE | VM_READ]				= __pgprot(0),
> +	[VM_EXEC]					= __pgprot(0),
> +	[VM_EXEC | VM_READ]				= __pgprot(0),
> +	[VM_EXEC | VM_WRITE]				= __pgprot(0),
> +	[VM_EXEC | VM_WRITE | VM_READ]			= __pgprot(0),
> +	[VM_SHARED]					= __pgprot(0),
> +	[VM_SHARED | VM_READ]				= __pgprot(0),
> +	[VM_SHARED | VM_WRITE]				= __pgprot(0),
> +	[VM_SHARED | VM_WRITE | VM_READ]		= __pgprot(0),
> +	[VM_SHARED | VM_EXEC]				= __pgprot(0),
> +	[VM_SHARED | VM_EXEC | VM_READ]			= __pgprot(0),
> +	[VM_SHARED | VM_EXEC | VM_WRITE]		= __pgprot(0),
> +	[VM_SHARED | VM_EXEC | VM_WRITE | VM_READ]	= __pgprot(0)
> +};

__pgprot(0) is 0 so you don't need to initialise the fields at all, it 
is zeroized at startup as part of BSS section.

> +
>   static void prot_init_common(unsigned long page_none,
>   			     unsigned long page_shared,
>   			     unsigned long page_copy,

> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index bc8f326be0ce..2254c1980c8e 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -420,11 +420,13 @@ extern unsigned int kobjsize(const void *objp);
>   #endif
>   #define VM_FLAGS_CLEAR	(ARCH_VM_PKEY_FLAGS | VM_ARCH_CLEAR)
>   
> +#ifndef CONFIG_ARCH_HAS_VM_GET_PAGE_PROT
>   /*
>    * mapping from the currently active vm_flags protection bits (the
>    * low four bits) to a page protection mask..
>    */
>   extern pgprot_t protection_map[16];
> +#endif
>   
>   /*
>    * The default fault flags that should be used by most of the
> 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
>   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

Why not let architectures provide their protection_map[] and keep that 
function ?

>   pgprot_t vm_get_page_prot(unsigned long vm_flags)
>   {
>   	return protection_map[vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)];