Patch "powerpc/vdso64: Use double word compare on pointers" has been added to the 4.8-stable tree

This is a note to let you know that I've just added the patch titled

powerpc/vdso64: Use double word compare on pointers

to the 4.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
powerpc-vdso64-use-double-word-compare-on-pointers.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Anton Blanchard <[email protected]>
Date: Sun, 25 Sep 2016 17:16:53 +1000
Subject: powerpc/vdso64: Use double word compare on pointers

From: Anton Blanchard <[email protected]>

commit 5045ea37377ce8cca6890d32b127ad6770e6dce5 upstream.

__kernel_get_syscall_map() and __kernel_clock_getres() use cmpli to check if the passed in pointer is non zero. cmpli maps to a 32 bit compare on binutils, so we ignore the top 32 bits.

A simple test case can be created by passing in a bogus pointer with the bottom 32 bits clear. Using a clk_id that is handled by the VDSO, then one that is handled by the kernel shows the problem:

  printf("%d\n", clock_getres(CLOCK_REALTIME, (void *)0x100000000));
  printf("%d\n", clock_getres(CLOCK_BOOTTIME, (void *)0x100000000));

And we get:

0
-1

The bigger issue is if we pass a valid pointer with the bottom 32 bits clear, in this case we will return success but won't write any data to the pointer.

I stumbled across this issue because the LLVM integrated assembler doesn't accept cmpli with 3 arguments. Fix this by converting them to cmpldi.

---
 arch/powerpc/kernel/vdso64/datapage.S     |    2 +-
 arch/powerpc/kernel/vdso64/gettimeofday.S |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

@@ -59,7 +59,7 @@ V_FUNCTION_BEGIN(__kernel_get_syscall_ma
 	bl	V_LOCAL_FUNC(__get_datapage)
 	mtlr	r12
 	addi	r3,r3,CFG_SYSCALL_MAP64
-	cmpli	cr0,r4,0
+	cmpldi	cr0,r4,0
 	crclr	cr0*4+so
 	beqlr
 	li	r0,NR_syscalls

@@ -145,7 +145,7 @@ V_FUNCTION_BEGIN(__kernel_clock_getres)
 	bne	cr0,99f
 
 	li	r3,0
-	cmpli	cr0,r4,0
+	cmpldi	cr0,r4,0
 	crclr	cr0*4+so
 	beqlr
 	lis	r5,CLOCK_REALTIME_RES@h

Patches currently in stable-queue which might be from [email protected] are

queue-4.8/powerpc-vdso64-use-double-word-compare-on-pointers.patch