The patch below does not apply to the 4.20-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 2a418cf3f5f1caf911af288e978d61c9844b0695 Mon Sep 17 00:00:00 2001

From: Andy Lutomirski luto@kernel.org Date: Fri, 22 Feb 2019 17:17:04 -0800 Subject: [PATCH] x86/uaccess: Don't leak the AC flag into __put_user() value evaluation

When calling __put_user(foo(), ptr), the __put_user() macro would call foo() in between __uaccess_begin() and __uaccess_end(). If that code were buggy, then those bugs would be run without SMAP protection.

Fortunately, there seem to be few instances of the problem in the kernel. Nevertheless, __put_user() should be fixed to avoid doing this. Therefore, evaluate __put_user()'s argument before setting AC.

This issue was noticed when an objtool hack by Peter Zijlstra complained about genregs_get() and I compared the assembly output to the C source.

[ bp: Massage commit message and fixed up whitespace. ]

Fixes: 11f1a4b9755f ("x86: reorganize SMAP handling in user space accesses") Signed-off-by: Andy Lutomirski luto@kernel.org Signed-off-by: Borislav Petkov bp@suse.de Acked-by: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Brian Gerst brgerst@gmail.com Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: Denys Vlasenko dvlasenk@redhat.com Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/20190225125231.845656645@infradead.org

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index a77445d1b034..28376aa2d053 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -284,7 +284,7 @@ do { \ __put_user_goto(x, ptr, "l", "k", "ir", label); \ break; \ case 8: \ - __put_user_goto_u64((__typeof__(*ptr))(x), ptr, label); \ + __put_user_goto_u64(x, ptr, label); \ break; \ default: \ __put_user_bad(); \ @@ -431,8 +431,10 @@ do { \ ({ \ __label__ __pu_label; \ int __pu_err = -EFAULT; \ + __typeof__(*(ptr)) __pu_val; \ + __pu_val = x; \ __uaccess_begin(); \ - __put_user_size((x), (ptr), (size), __pu_label); \ + __put_user_size(__pu_val, (ptr), (size), __pu_label); \ __pu_err = 0; \ __pu_label: \ __uaccess_end(); \