[PATCH ] powerpc/pkeys: Detach execute_only key on !PROT_EXEC

[PATCH ] powerpc/pkeys: Detach execute_only key on !PROT_EXEC

[Ram Pai]

Disassociate the exec_key from a VMA if the VMA permission is not
PROT_EXEC anymore.  Otherwise the exec_only key continues to be
associated with the vma, causing unexpected behavior.

The problem was reported on x86 by Shakeel Butt,
which is also applicable on powerpc.

cc: Shakeel Butt <shakeelb@google.com>
Reported-by: Shakeel Butt <shakeelb@google.com>
Fixes 5586cf6 ("powerpc: introduce execute-only pkey")
Signed-off-by: Ram Pai <linuxram@us.ibm.com>
---
 arch/powerpc/mm/pkeys.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
index e81d59e..fdeb9f5 100644
--- a/arch/powerpc/mm/pkeys.c
+++ b/arch/powerpc/mm/pkeys.c
@@ -425,9 +425,9 @@ int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot,
 {
 	/*
 	 * If the currently associated pkey is execute-only, but the requested
-	 * protection requires read or write, move it back to the default pkey.
+	 * protection is not execute-only, move it back to the default pkey.
 	 */
-	if (vma_is_pkey_exec_only(vma) && (prot & (PROT_READ | PROT_WRITE)))
+	if (vma_is_pkey_exec_only(vma) && (prot != PROT_EXEC))
 		return 0;
 
 	/*
-- 
1.7.1

Re: [PATCH ] powerpc/pkeys: Detach execute_only key on !PROT_EXEC

[Thiago Jung Bauermann]

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

> Disassociate the exec_key from a VMA if the VMA permission is not
> PROT_EXEC anymore.  Otherwise the exec_only key continues to be
> associated with the vma, causing unexpected behavior.
>
> The problem was reported on x86 by Shakeel Butt,
> which is also applicable on powerpc.
>
> cc: Shakeel Butt <shakeelb@google.com>
> Reported-by: Shakeel Butt <shakeelb@google.com>
> Fixes 5586cf6 ("powerpc: introduce execute-only pkey")
       ^
         Missing a colon here.

> Signed-off-by: Ram Pai <linuxram@us.ibm.com>
> ---
>  arch/powerpc/mm/pkeys.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
> index e81d59e..fdeb9f5 100644
> --- a/arch/powerpc/mm/pkeys.c
> +++ b/arch/powerpc/mm/pkeys.c
> @@ -425,9 +425,9 @@ int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot,
>  {
>  	/*
>  	 * If the currently associated pkey is execute-only, but the requested
> -	 * protection requires read or write, move it back to the default pkey.
> +	 * protection is not execute-only, move it back to the default pkey.
>  	 */
> -	if (vma_is_pkey_exec_only(vma) && (prot & (PROT_READ | PROT_WRITE)))
> +	if (vma_is_pkey_exec_only(vma) && (prot != PROT_EXEC))
>  		return 0;
>
>  	/*

I think I'm slow today. It took me a while to figure out why this is
buggy. It will leave the VMA with the execute-only pkey if prot = 0.
Other bit combinations work fine IIUC.

Reviewed-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>

--
Thiago Jung Bauermann
IBM Linux Technology Center

Re: powerpc/pkeys: Detach execute_only key on !PROT_EXEC

[Michael Ellerman]

On Fri, 2018-05-04 at 20:01:51 UTC, Ram Pai wrote:
> Disassociate the exec_key from a VMA if the VMA permission is not
> PROT_EXEC anymore.  Otherwise the exec_only key continues to be
> associated with the vma, causing unexpected behavior.
> 
> The problem was reported on x86 by Shakeel Butt,
> which is also applicable on powerpc.
> 
> cc: Shakeel Butt <shakeelb@google.com>
> Reported-by: Shakeel Butt <shakeelb@google.com>
> Fixes 5586cf6 ("powerpc: introduce execute-only pkey")
> Signed-off-by: Ram Pai <linuxram@us.ibm.com>
> Reviewed-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/eabdb8ca8690eedd461e61ea778059

cheers