Subject: Re: [PATCH v2 37/37] powerpc: Support execute-only on all powerpc

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Thu, 02 Nov 2023 11:09:37 +0530

Christophe Leroy <[email-masked]> writes:

> Introduce PAGE_EXECONLY_X macro which provides exec-only rights.
> The _X may be seen as redundant with the EXECONLY but it helps
> keep consistancy, all macros having the EXEC right have _X.
>
> And put it next to PAGE_NONE as PAGE_EXECONLY_X is
> somehow PAGE_NONE + EXEC just like all other SOMETHING_X are
> just SOMETHING + EXEC.
>
> On book3s/64 PAGE_EXECONLY becomes PAGE_READONLY_X.
>
> On book3s/64, as PAGE_EXECONLY is only valid for Radix add
> VM_READ flag in vm_get_page_prot() for non-Radix.
>
> And update access_error() so that a non exec fault on a VM_EXEC only
> mapping is always invalid, even when the underlying layer don't
> always generate a fault for that.
>
> For 8xx, set PAGE_EXECONLY_X as _PAGE_NA | _PAGE_EXEC.
> For others, only set it as just _PAGE_EXEC
>
> With that change, 8xx, e500 and 44x fully honor execute-only
> protection.
>
> On 40x that is a partial implementation of execute-only. The
> implementation won't be complete because once a TLB has been loaded
> via the Instruction TLB miss handler, it will be possible to read
> the page. But at least it can't be read unless it is executed first.
>
> On 603 MMU, TLB missed are handled by SW and there are separate
> DTLB and ITLB. Execute-only is therefore now supported by not loading
> DTLB when read access is not permitted.
>
> On hash (604) MMU it is more tricky because hash table is common to
> load/store and execute. Nevertheless it is still possible to check
> whether _PAGE_READ is set before loading hash table for a load/store
> access. At least it can't be read unless it is executed first.
>
> Signed-off-by: Christophe Leroy <[email-masked]>
> Cc: Russell Currey <[email-masked]>
> Cc: Kees Cook <[email-masked]>
> ---
>  arch/powerpc/include/asm/book3s/32/pgtable.h |  2 +-
>  arch/powerpc/include/asm/book3s/64/pgtable.h |  4 +---
>  arch/powerpc/include/asm/nohash/32/pte-8xx.h |  1 +
>  arch/powerpc/include/asm/nohash/pgtable.h    |  2 +-
>  arch/powerpc/include/asm/nohash/pte-e500.h   |  1 +
>  arch/powerpc/include/asm/pgtable-masks.h     |  2 ++
>  arch/powerpc/mm/book3s64/pgtable.c           | 10 ++++------
>  arch/powerpc/mm/fault.c                      |  9 +++++----
>  arch/powerpc/mm/pgtable.c                    |  4 ++--
>  9 files changed, 18 insertions(+), 17 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/book3s/32/pgtable.h b/arch/powerpc/include/asm/book3s/32/pgtable.h
> index 244621c88510..52971ee30717 100644
> --- a/arch/powerpc/include/asm/book3s/32/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/32/pgtable.h
> @@ -425,7 +425,7 @@ static inline bool pte_access_permitted(pte_t pte, bool write)
>  {
>  	/*
>  	 * A read-only access is controlled by _PAGE_READ bit.
> -	 * We have _PAGE_READ set for WRITE and EXECUTE
> +	 * We have _PAGE_READ set for WRITE
>  	 */
>  	if (!pte_present(pte) || !pte_read(pte))
>  		return false; 
>

Should this now be updated to check for EXEC bit ? 

> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
> index 0fd12bdc7b5e..751b01227e36 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> @@ -18,6 +18,7 @@
>  #define _PAGE_WRITE		0x00002 /* write access allowed */
>  #define _PAGE_READ		0x00004	/* read access allowed */
>  #define _PAGE_NA		_PAGE_PRIVILEGED
> +#define _PAGE_NAX		_PAGE_EXEC
>  #define _PAGE_RO		_PAGE_READ
>  #define _PAGE_ROX		(_PAGE_READ | _PAGE_EXEC)
>  #define _PAGE_RW		(_PAGE_READ | _PAGE_WRITE)
> @@ -141,9 +142,6 @@
>  
>  #include <asm/pgtable-masks.h>
>  
> -/* Radix only, Hash uses PAGE_READONLY_X + execute-only pkey instead */
> -#define PAGE_EXECONLY	__pgprot(_PAGE_BASE | _PAGE_EXEC)
> -
>  /* Permission masks used for kernel mappings */
>  #define PAGE_KERNEL	__pgprot(_PAGE_BASE | _PAGE_KERNEL_RW)
>  #define PAGE_KERNEL_NC	__pgprot(_PAGE_BASE_NC | _PAGE_KERNEL_RW | _PAGE_TOLERANT)
> diff --git a/arch/powerpc/include/asm/nohash/32/pte-8xx.h b/arch/powerpc/include/asm/nohash/32/pte-8xx.h
> index 1ee38befd29a..137dc3c84e45 100644
> --- a/arch/powerpc/include/asm/nohash/32/pte-8xx.h
> +++ b/arch/powerpc/include/asm/nohash/32/pte-8xx.h
> @@ -48,6 +48,7 @@
>  
>  #define _PAGE_HUGE	0x0800	/* Copied to L1 PS bit 29 */
>  
> +#define _PAGE_NAX	(_PAGE_NA | _PAGE_EXEC)
>  #define _PAGE_ROX	(_PAGE_RO | _PAGE_EXEC)
>  #define _PAGE_RW	0
>  #define _PAGE_RWX	_PAGE_EXEC
> diff --git a/arch/powerpc/include/asm/nohash/pgtable.h b/arch/powerpc/include/asm/nohash/pgtable.h
> index f922c84b23eb..a50be1de9f83 100644
> --- a/arch/powerpc/include/asm/nohash/pgtable.h
> +++ b/arch/powerpc/include/asm/nohash/pgtable.h
> @@ -203,7 +203,7 @@ static inline bool pte_access_permitted(pte_t pte, bool write)
>  {
>  	/*
>  	 * A read-only access is controlled by _PAGE_READ bit.
> -	 * We have _PAGE_READ set for WRITE and EXECUTE
> +	 * We have _PAGE_READ set for WRITE
>  	 */
>  	if (!pte_present(pte) || !pte_read(pte))
>  		return false;
>

Same here. if so I guess book3s/64 also will need an update?

> diff --git a/arch/powerpc/include/asm/nohash/pte-e500.h b/arch/powerpc/include/asm/nohash/pte-e500.h
> index 31d2c3ea7df8..f516f0b5b7a8 100644
> --- a/arch/powerpc/include/asm/nohash/pte-e500.h
> +++ b/arch/powerpc/include/asm/nohash/pte-e500.h
> @@ -57,6 +57,7 @@
>  #define _PAGE_KERNEL_ROX	(_PAGE_BAP_SR | _PAGE_BAP_SX)
>  
>  #define _PAGE_NA	0
> +#define _PAGE_NAX	_PAGE_BAP_UX
>  #define _PAGE_RO	_PAGE_READ
>  #define _PAGE_ROX	(_PAGE_READ | _PAGE_BAP_UX)
>  #define _PAGE_RW	(_PAGE_READ | _PAGE_WRITE)
> diff --git a/arch/powerpc/include/asm/pgtable-masks.h b/arch/powerpc/include/asm/pgtable-masks.h
> index 808a3b9e8fc0..6e8e2db26a5a 100644
> --- a/arch/powerpc/include/asm/pgtable-masks.h
> +++ b/arch/powerpc/include/asm/pgtable-masks.h
> @@ -4,6 +4,7 @@
>  
>  #ifndef _PAGE_NA
>  #define _PAGE_NA	0
> +#define _PAGE_NAX	_PAGE_EXEC
>  #define _PAGE_RO	_PAGE_READ
>  #define _PAGE_ROX	(_PAGE_READ | _PAGE_EXEC)
>  #define _PAGE_RW	(_PAGE_READ | _PAGE_WRITE)
> @@ -20,6 +21,7 @@
>  
>  /* Permission masks used to generate the __P and __S table */
>  #define PAGE_NONE	__pgprot(_PAGE_BASE | _PAGE_NA)
> +#define PAGE_EXECONLY_X	__pgprot(_PAGE_BASE | _PAGE_NAX)
>  #define PAGE_SHARED	__pgprot(_PAGE_BASE | _PAGE_RW)
>  #define PAGE_SHARED_X	__pgprot(_PAGE_BASE | _PAGE_RWX)
>  #define PAGE_COPY	__pgprot(_PAGE_BASE | _PAGE_RO)
> diff --git a/arch/powerpc/mm/book3s64/pgtable.c b/arch/powerpc/mm/book3s64/pgtable.c
> index 8f8a62d3ff4d..be229290a6a7 100644
> --- a/arch/powerpc/mm/book3s64/pgtable.c
> +++ b/arch/powerpc/mm/book3s64/pgtable.c
> @@ -635,12 +635,10 @@ pgprot_t vm_get_page_prot(unsigned long vm_flags)
>  	unsigned long prot;
>  
>  	/* Radix supports execute-only, but protection_map maps X -> RX */
> -	if (radix_enabled() && ((vm_flags & VM_ACCESS_FLAGS) == VM_EXEC)) {
> -		prot = pgprot_val(PAGE_EXECONLY);
> -	} else {
> -		prot = pgprot_val(protection_map[vm_flags &
> -						 (VM_ACCESS_FLAGS | VM_SHARED)]);
> -	}
> +	if (!radix_enabled() && ((vm_flags & VM_ACCESS_FLAGS) == VM_EXEC))
> +		vm_flags |= VM_READ;
> +
> +	prot = pgprot_val(protection_map[vm_flags & (VM_ACCESS_FLAGS | VM_SHARED)]);
>  
>  	if (vm_flags & VM_SAO)
>  		prot |= _PAGE_SAO;
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index b1723094d464..9e49ede2bc1c 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -266,14 +266,15 @@ static bool access_error(bool is_write, bool is_exec, struct vm_area_struct *vma
>  	}
>  
>  	/*
> -	 * VM_READ, VM_WRITE and VM_EXEC all imply read permissions, as
> -	 * defined in protection_map[].  Read faults can only be caused by
> -	 * a PROT_NONE mapping, or with a PROT_EXEC-only mapping on Radix.
> +	 * VM_READ, VM_WRITE and VM_EXEC may imply read permissions, as
> +	 * defined in protection_map[].  In that case Read faults can only be
> +	 * caused by a PROT_NONE mapping. However a non exec access on a
> +	 * VM_EXEC only mapping is invalid anyway, so report it as such.
>  	 */
>  	if (unlikely(!vma_is_accessible(vma)))
>  		return true;
>  
> -	if (unlikely(radix_enabled() && ((vma->vm_flags & VM_ACCESS_FLAGS) == VM_EXEC)))
> +	if ((vma->vm_flags & VM_ACCESS_FLAGS) == VM_EXEC)
>  		return true;
>  
>  	/*
> diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
> index 781a68c69c2f..79508c1d15d7 100644
> --- a/arch/powerpc/mm/pgtable.c
> +++ b/arch/powerpc/mm/pgtable.c
> @@ -492,7 +492,7 @@ const pgprot_t protection_map[16] = {
>  	[VM_READ]					= PAGE_READONLY,
>  	[VM_WRITE]					= PAGE_COPY,
>  	[VM_WRITE | VM_READ]				= PAGE_COPY,
> -	[VM_EXEC]					= PAGE_READONLY_X,
> +	[VM_EXEC]					= PAGE_EXECONLY_X,
>  	[VM_EXEC | VM_READ]				= PAGE_READONLY_X,
>  	[VM_EXEC | VM_WRITE]				= PAGE_COPY_X,
>  	[VM_EXEC | VM_WRITE | VM_READ]			= PAGE_COPY_X,
> @@ -500,7 +500,7 @@ const pgprot_t protection_map[16] = {
>  	[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]				= PAGE_EXECONLY_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
> -- 
> 2.41.0