Re: pkeys on POWER: Access rights not reset on execve

[Ram Pai <linuxram@us.ibm.com>]

On Mon, May 21, 2018 at 01:29:11PM +0200, Florian Weimer wrote:
> On 05/20/2018 09:11 PM, Ram Pai wrote:
> >Florian,
> >
> >	Does the following patch fix the problem for you?  Just like x86
> >	I am enabling all keys in the UAMOR register during
> >	initialization itself. Hence any key created by any thread at
> >	any time, will get activated on all threads. So any thread
> >	can change the permission on that key. Smoke tested it
> >	with your test program.
> 
> I think this goes in the right direction, but the AMR value after
> fork is still strange:
> 
> AMR (PID 34912): 0x0000000000000000
> AMR after fork (PID 34913): 0x0000000000000000
> AMR (PID 34913): 0x0000000000000000
> Allocated key in subprocess (PID 34913): 2
> Allocated key (PID 34912): 2
> Setting AMR: 0xffffffffffffffff
> New AMR value (PID 34912): 0x0fffffffffffffff
> About to call execl (PID 34912) ...
> AMR (PID 34912): 0x0fffffffffffffff
> AMR after fork (PID 34914): 0x0000000000000003
> AMR (PID 34914): 0x0000000000000003
> Allocated key in subprocess (PID 34914): 2
> Allocated key (PID 34912): 2
> Setting AMR: 0xffffffffffffffff
> New AMR value (PID 34912): 0x0fffffffffffffff
> 
> I mean this line:
> 
> AMR after fork (PID 34914): 0x0000000000000003
> 
> Shouldn't it be the same as in the parent process?

Fixed it. Please try this patch. If it all works to your satisfaction, I
will clean it up further and send to Michael Ellermen(ppc maintainer).


commit 51f4208ed5baeab1edb9b0f8b68d7144449b3527
Author: Ram Pai <linuxram@us.ibm.com>
Date:   Sun Jun 3 14:44:32 2018 -0500

    Fix for the fork bug.
    
    Signed-off-by: Ram Pai <linuxram@us.ibm.com>

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 1237f13..999dd08 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -582,6 +582,7 @@ static void save_all(struct task_struct *tsk)
 		__giveup_spe(tsk);
 
 	msr_check_and_clear(msr_all_available);
+	thread_pkey_regs_save(&tsk->thread);
 }
 
 void flush_all_to_thread(struct task_struct *tsk)
diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
index ab4519a..af6aa4a 100644
--- a/arch/powerpc/mm/pkeys.c
+++ b/arch/powerpc/mm/pkeys.c
@@ -294,6 +294,7 @@ void thread_pkey_regs_save(struct thread_struct *thread)
 	 */
 	thread->amr = read_amr();
 	thread->iamr = read_iamr();
+	thread->uamor = read_uamor();
 }
 
 void thread_pkey_regs_restore(struct thread_struct *new_thread,
@@ -315,9 +316,13 @@ void thread_pkey_regs_init(struct thread_struct *thread)
 	if (static_branch_likely(&pkey_disabled))
 		return;
 
-	thread->amr = read_amr() & pkey_amr_mask;
-	thread->iamr = read_iamr() & pkey_iamr_mask;
+	thread->amr = pkey_amr_mask;
+	thread->iamr = pkey_iamr_mask;
 	thread->uamor = pkey_uamor_mask;
+
+	write_uamor(pkey_uamor_mask);
+	write_amr(pkey_amr_mask);
+	write_iamr(pkey_iamr_mask);
 }
 
 static inline bool pkey_allows_readwrite(int pkey)


> 
> Thanks,
> Florian

-- 
Ram Pai