On Sun, Mar 03, 2019 at 07:27:24PM +0300, Maxim Zhukov wrote:

From: Andy Lutomirski luto@kernel.org

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

---

arch/x86/include/asm/uaccess.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index a8d85a687cf4..39bbc225558c 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -292,7 +292,7 @@ do { \ __put_user_asm(x, ptr, retval, "l", "k", "ir", errret); \ break; \ case 8: \

• __put_user_asm_u64((__typeof__(*ptr))(x), ptr, retval,	\
  

• __put_user_asm_u64(x, ptr, retval,	\
  	   errret);				\
  

  break; \ default: \

@@ -427,8 +427,10 @@ do { \ #define __put_user_nocheck(x, ptr, size) \ ({ \ int __pu_err; \

• __typeof__(*(ptr)) __pu_val; \ __uaccess_begin(); \

• __put_user_size((x), (ptr), (size), __pu_err, -EFAULT); \

• __pu_val = x; \

This is incorrect, __pu_val's assignment should be before __uaccess_begin like in the original patch (which is the point of the patch in the first place).

Cheers, Nathan

• __put_user_size(__pu_val, (ptr), (size), __pu_err, -EFAULT); \ __uaccess_end(); \ __builtin_expect(__pu_err, 0); \

})

2.21.0