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

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 <redacted>
Reported-by: Shakeel Butt <redacted>
Fixes 5586cf6 ("powerpc: introduce execute-only pkey")
Signed-off-by: Ram Pai <redacted>
---
 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

Ram Pai [off-list ref] 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 <redacted>
Reported-by: Shakeel Butt <redacted>
Fixes 5586cf6 ("powerpc: introduce execute-only pkey")

       ^
         Missing a colon here.

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 <redacted>

--
Thiago Jung Bauermann
IBM Linux Technology Center

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 <redacted>
Reported-by: Shakeel Butt <redacted>
Fixes 5586cf6 ("powerpc: introduce execute-only pkey")
Signed-off-by: Ram Pai <redacted>
Reviewed-by: Thiago Jung Bauermann <redacted>

Applied to powerpc next, thanks.

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

cheers