ARC: uaccess: get_user to zero out dest in cause of fault

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
Cc: stable@vger.kernel.org
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/arch/arc/include/asm/uaccess.h b/arch/arc/include/asm/uaccess.h
index a78d5670884f32490d2341b2468bf606258b6654..41faf17cd28d2ced7461f4e6860d2456fb49f8ae 100644 (file)
--- 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"   \