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Subject[PATCH 3.16 278/346] ARC: uaccess: get_user to zero out dest in cause of fault
3.16.39-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Vineet Gupta <Vineet.Gupta1@synopsys.com>

commit 05d9d0b96e53c52a113fd783c0c97c830c8dc7af upstream.

Al reported potential issue with ARC get_user() as it wasn't clearing
out destination pointer in case of fault due to bad address etc.

Verified using following

| {
| u32 bogus1 = 0xdeadbeef;
| u64 bogus2 = 0xdead;
| int rc1, rc2;
|
| pr_info("Orig values %x %llx\n", bogus1, bogus2);
| rc1 = get_user(bogus1, (u32 __user *)0x40000000);
| rc2 = get_user(bogus2, (u64 __user *)0x50000000);
| pr_info("access %d %d, new values %x %llx\n",
| rc1, rc2, bogus1, bogus2);
| }

| [ARCLinux]# insmod /mnt/kernel-module/qtn.ko
| Orig values deadbeef dead
| access -14 -14, new values 0 0

Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-snps-arc@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
arch/arc/include/asm/uaccess.h | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

--- a/arch/arc/include/asm/uaccess.h
+++ b/arch/arc/include/asm/uaccess.h
@@ -83,7 +83,10 @@
"2: ;nop\n" \
" .section .fixup, \"ax\"\n" \
" .align 4\n" \
- "3: mov %0, %3\n" \
+ "3: # return -EFAULT\n" \
+ " mov %0, %3\n" \
+ " # zero out dst ptr\n" \
+ " mov %1, 0\n" \
" j 2b\n" \
" .previous\n" \
" .section __ex_table, \"a\"\n" \
@@ -101,7 +104,11 @@
"2: ;nop\n" \
" .section .fixup, \"ax\"\n" \
" .align 4\n" \
- "3: mov %0, %3\n" \
+ "3: # return -EFAULT\n" \
+ " mov %0, %3\n" \
+ " # zero out dst ptr\n" \
+ " mov %1, 0\n" \
+ " mov %R1, 0\n" \
" j 2b\n" \
" .previous\n" \
" .section __ex_table, \"a\"\n" \
\
 
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