On Sun, Mar 03, 2019 at 07:27:24PM +0300, Maxim Zhukov wrote:
> From: Andy Lutomirski <luto@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> Signed-off-by: Borislav Petkov <bp@xxxxxxx>
> Acked-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Brian Gerst <brgerst@xxxxxxxxx>
> Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Link: http://lkml.kernel.org/r/20190225125231.845656645@xxxxxxxxxxxxx
> ---
> 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
>
