linux-kernel - Re: [RFC v6 19/62] powerpc: ability to create execute-disabled pkeys

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Message-Id: <87bmo63p7c.fsf@linux.vnet.ibm.com>
Date:   Thu, 27 Jul 2017 11:54:31 -0300
From:   Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>
To:     Ram Pai <linuxram@...ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
        linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org,
        arnd@...db.de, corbet@....net, mhocko@...nel.org,
        dave.hansen@...el.com, mingo@...hat.com, paulus@...ba.org,
        aneesh.kumar@...ux.vnet.ibm.com, akpm@...ux-foundation.org,
        khandual@...ux.vnet.ibm.com
Subject: Re: [RFC v6 19/62] powerpc: ability to create execute-disabled pkeys


Ram Pai <linuxram@...ibm.com> writes:

> --- a/arch/powerpc/include/asm/pkeys.h
> +++ b/arch/powerpc/include/asm/pkeys.h
> @@ -2,6 +2,18 @@
>  #define _ASM_PPC64_PKEYS_H
>
>  extern bool pkey_inited;
> +/* override any generic PKEY Permission defines */
> +#undef  PKEY_DISABLE_ACCESS
> +#define PKEY_DISABLE_ACCESS    0x1
> +#undef  PKEY_DISABLE_WRITE
> +#define PKEY_DISABLE_WRITE     0x2
> +#undef  PKEY_DISABLE_EXECUTE
> +#define PKEY_DISABLE_EXECUTE   0x4
> +#undef  PKEY_ACCESS_MASK
> +#define PKEY_ACCESS_MASK       (PKEY_DISABLE_ACCESS |\
> +				PKEY_DISABLE_WRITE  |\
> +				PKEY_DISABLE_EXECUTE)
> +

Is it ok to #undef macros from another header? Especially since said
header is in uapi (include/uapi/asm-generic/mman-common.h).

Also, it's unnecessary to undef the _ACCESS and _WRITE macros since they
are identical to the original definition. And since these macros are
originally defined in an uapi header, the powerpc-specific ones should
be in an uapi header as well, if I understand it correctly.

An alternative solution is to define only PKEY_DISABLE_EXECUTE in
arch/powerpc/include/uapi/asm/mman.h and then test for its existence to
properly define PKEY_ACCESS_MASK in
include/uapi/asm-generic/mman-common.h. What do you think of the code
below?

diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h
index e31f5ee8e81f..67e6a3a343ae 100644
--- a/arch/powerpc/include/asm/pkeys.h
+++ b/arch/powerpc/include/asm/pkeys.h
@@ -4,17 +4,6 @@
 #include <asm/firmware.h>
 
 extern bool pkey_inited;
-/* override any generic PKEY Permission defines */
-#undef  PKEY_DISABLE_ACCESS
-#define PKEY_DISABLE_ACCESS    0x1
-#undef  PKEY_DISABLE_WRITE
-#define PKEY_DISABLE_WRITE     0x2
-#undef  PKEY_DISABLE_EXECUTE
-#define PKEY_DISABLE_EXECUTE   0x4
-#undef  PKEY_ACCESS_MASK
-#define PKEY_ACCESS_MASK       (PKEY_DISABLE_ACCESS |\
-				PKEY_DISABLE_WRITE  |\
-				PKEY_DISABLE_EXECUTE)
 
 #define ARCH_VM_PKEY_FLAGS (VM_PKEY_BIT0 | VM_PKEY_BIT1 | VM_PKEY_BIT2 | \
 				VM_PKEY_BIT3 | VM_PKEY_BIT4)
diff --git a/arch/powerpc/include/uapi/asm/mman.h b/arch/powerpc/include/uapi/asm/mman.h
index ab45cc2f3101..dee43feb7c53 100644
--- a/arch/powerpc/include/uapi/asm/mman.h
+++ b/arch/powerpc/include/uapi/asm/mman.h
@@ -45,4 +45,6 @@
 #define MAP_HUGE_1GB	(30 << MAP_HUGE_SHIFT)	/* 1GB   HugeTLB Page */
 #define MAP_HUGE_16GB	(34 << MAP_HUGE_SHIFT)	/* 16GB  HugeTLB Page */
 
+#define PKEY_DISABLE_EXECUTE   0x4
+
 #endif /* _UAPI_ASM_POWERPC_MMAN_H */
diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
index 72eb9a1bde79..777f8f8dff47 100644
--- a/arch/powerpc/mm/pkeys.c
+++ b/arch/powerpc/mm/pkeys.c
@@ -12,7 +12,7 @@
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  * more details.
  */
-#include <uapi/asm-generic/mman-common.h>
+#include <asm/mman.h>
 #include <linux/pkeys.h>                /* PKEY_*                       */
 
 bool pkey_inited;
diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
index 8c27db0c5c08..93e3841d9ada 100644
--- a/include/uapi/asm-generic/mman-common.h
+++ b/include/uapi/asm-generic/mman-common.h
@@ -74,7 +74,15 @@
 
 #define PKEY_DISABLE_ACCESS	0x1
 #define PKEY_DISABLE_WRITE	0x2
+
+/* The arch-specific code may define PKEY_DISABLE_EXECUTE */
+#ifdef PKEY_DISABLE_EXECUTE
+#define PKEY_ACCESS_MASK       (PKEY_DISABLE_ACCESS |	\
+				PKEY_DISABLE_WRITE  |	\
+				PKEY_DISABLE_EXECUTE)
+#else
 #define PKEY_ACCESS_MASK	(PKEY_DISABLE_ACCESS |\
 				 PKEY_DISABLE_WRITE)
+#endif
 
 #endif /* __ASM_GENERIC_MMAN_COMMON_H */


> diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
> index 98d0391..b9ad98d 100644
> --- a/arch/powerpc/mm/pkeys.c
> +++ b/arch/powerpc/mm/pkeys.c
> @@ -73,6 +73,7 @@ int __arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
>  		unsigned long init_val)
>  {
>  	u64 new_amr_bits = 0x0ul;
> +	u64 new_iamr_bits = 0x0ul;
>
>  	if (!is_pkey_enabled(pkey))
>  		return -1;
> @@ -85,5 +86,14 @@ int __arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
>
>  	init_amr(pkey, new_amr_bits);
>
> +	/*
> +	 * By default execute is disabled.
> +	 * To enable execute, PKEY_ENABLE_EXECUTE
> +	 * needs to be specified.
> +	 */
> +	if ((init_val & PKEY_DISABLE_EXECUTE))
> +		new_iamr_bits |= IAMR_EX_BIT;
> +
> +	init_iamr(pkey, new_iamr_bits);
>  	return 0;
>  }

The comment seems to be from an earlier version which has the logic
inverted, and there is no PKEY_ENABLE_EXECUTE. Should the comment be
updated to the following?

    By default execute is enabled.
    To disable execute, PKEY_DISABLE_EXECUTE needs to be specified.

-- 
Thiago Jung Bauermann
IBM Linux Technology Center