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    Subject[PATCH 5.2 112/124] x86/uaccess: Dont leak the AC flags into __get_user() argument evaluation
    Date
    From: Peter Zijlstra <peterz@infradead.org>

    [ Upstream commit 9b8bd476e78e89c9ea26c3b435ad0201c3d7dbf5 ]

    Identical to __put_user(); the __get_user() argument evalution will too
    leak UBSAN crud into the __uaccess_begin() / __uaccess_end() region.
    While uncommon this was observed to happen for:

    drivers/xen/gntdev.c: if (__get_user(old_status, batch->status[i]))

    where UBSAN added array bound checking.

    This complements commit:

    6ae865615fc4 ("x86/uaccess: Dont leak the AC flag into __put_user() argument evaluation")

    Tested-by Sedat Dilek <sedat.dilek@gmail.com>
    Reported-by: Randy Dunlap <rdunlap@infradead.org>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
    Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
    Cc: broonie@kernel.org
    Cc: sfr@canb.auug.org.au
    Cc: akpm@linux-foundation.org
    Cc: Randy Dunlap <rdunlap@infradead.org>
    Cc: mhocko@suse.cz
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Link: https://lkml.kernel.org/r/20190829082445.GM2369@hirez.programming.kicks-ass.net
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/x86/include/asm/uaccess.h | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
    index c82abd6e4ca39..869794bd0fd98 100644
    --- a/arch/x86/include/asm/uaccess.h
    +++ b/arch/x86/include/asm/uaccess.h
    @@ -442,8 +442,10 @@ __pu_label: \
    ({ \
    int __gu_err; \
    __inttype(*(ptr)) __gu_val; \
    + __typeof__(ptr) __gu_ptr = (ptr); \
    + __typeof__(size) __gu_size = (size); \
    __uaccess_begin_nospec(); \
    - __get_user_size(__gu_val, (ptr), (size), __gu_err, -EFAULT); \
    + __get_user_size(__gu_val, __gu_ptr, __gu_size, __gu_err, -EFAULT); \
    __uaccess_end(); \
    (x) = (__force __typeof__(*(ptr)))__gu_val; \
    __builtin_expect(__gu_err, 0); \
    --
    2.20.1


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