linux-kernel - Re: [git pull] uaccess fixes

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Message-ID: <20160915013529.GH2356@ZenIV.linux.org.uk>
Date:   Thu, 15 Sep 2016 02:35:29 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [git pull] uaccess fixes

On Wed, Sep 14, 2016 at 04:47:47PM +0100, Al Viro wrote:
> 	Fixes for broken uaccess primitives - mostly lack of proper zeroing
> in copy_from_user()/get_user()/__get_user(), but for several architectures
> there's more (broken clear_user() on frv and strncpy_from_user() on hexagon).
> All of that is rc2-based stable fodder; usercopy stuff that went into mainline
> since then has added 3 conflicts - in parisc, ppc and itanic uaccess.h.
> Conflicts are trivial; I've pushed my variant of conflict resolution into
> #proposed-merge.

And a bit that has sat in a different branch since mid-August:

[x86] fix minor infoleak in get_user_ex()

get_user_ex(x, ptr) should zero x on failure.  It's not a lot of a leak
(at most we are leaking uninitialized 64bit value off the kernel stack,
and in a fairly constrained situation, at that), but the fix is trivial,
so...

Cc: stable@...r.kernel.org
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index a0ae610..7821921 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -433,7 +433,11 @@ do {									\
 #define __get_user_asm_ex(x, addr, itype, rtype, ltype)			\
 	asm volatile("1:	mov"itype" %1,%"rtype"0\n"		\
 		     "2:\n"						\
-		     _ASM_EXTABLE_EX(1b, 2b)				\
+		     ".section .fixup,\"ax\"\n"				\
+                     "3:xor"itype" %"rtype"0,%"rtype"0\n"		\
+		     "  jmp 2b\n"					\
+		     ".previous\n"					\
+		     _ASM_EXTABLE_EX(1b, 3b)				\
 		     : ltype(x) : "m" (__m(addr)))
 
 #define __put_user_nocheck(x, ptr, size)			\