[PATCH 3.2 032/126] powerpc/vdso64: Use double word compare on pointers

Ben Hutchings
2017-02-16T00:34:59Z

From: Anton Blanchard <anton@samba.org>

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.

Fixes: a7f290dad32e ("[PATCH] powerpc: Merge vdso's and add vdso support to 32 bits kernel")
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
arch/powerpc/kernel/vdso64/datapage.S | 2 +-
arch/powerpc/kernel/vdso64/gettimeofday.S | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

--- a/arch/powerpc/kernel/vdso64/datapage.S
+++ b/arch/powerpc/kernel/vdso64/datapage.S
@@ -57,7 +57,7 @@ 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
--- a/arch/powerpc/kernel/vdso64/gettimeofday.S
+++ b/arch/powerpc/kernel/vdso64/gettimeofday.S
@@ -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