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    Subject[PATCH 4.4 054/230] x86/uaccess: Dont leak the AC flag into __put_user() value evaluation
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Andy Lutomirski <luto@kernel.org>

    commit 2a418cf3f5f1caf911af288e978d61c9844b0695 upstream.

    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
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/include/asm/uaccess.h | 7 ++++---
    1 file changed, 4 insertions(+), 3 deletions(-)

    --- a/arch/x86/include/asm/uaccess.h
    +++ b/arch/x86/include/asm/uaccess.h
    @@ -314,8 +314,7 @@ do { \
    __put_user_asm(x, ptr, retval, "l", "k", "ir", errret); \
    break; \
    case 8: \
    - __put_user_asm_u64((__typeof__(*ptr))(x), ptr, retval, \
    - errret); \
    + __put_user_asm_u64(x, ptr, retval, errret); \
    break; \
    default: \
    __put_user_bad(); \
    @@ -426,8 +425,10 @@ do { \
    #define __put_user_nocheck(x, ptr, size) \
    ({ \
    int __pu_err; \
    + __typeof__(*(ptr)) __pu_val; \
    + __pu_val = x; \
    __uaccess_begin(); \
    - __put_user_size((x), (ptr), (size), __pu_err, -EFAULT); \
    + __put_user_size(__pu_val, (ptr), (size), __pu_err, -EFAULT);\
    __uaccess_end(); \
    __builtin_expect(__pu_err, 0); \
    })

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