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    Subject[PATCH 4.14 053/115] powerpc/uaccess: Enable get_user(u64, *p) on 32-bit
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

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

    From: Michael Ellerman <mpe@ellerman.id.au>

    [ Upstream commit f7a6947cd49b7ff4e03f1b4f7e7b223003d752ca ]

    Currently if you build a 32-bit powerpc kernel and use get_user() to
    load a u64 value it will fail to build with eg:

    kernel/rseq.o: In function `rseq_get_rseq_cs':
    kernel/rseq.c:123: undefined reference to `__get_user_bad'

    This is hitting the check in __get_user_size() that makes sure the
    size we're copying doesn't exceed the size of the destination:

    #define __get_user_size(x, ptr, size, retval)
    do {
    retval = 0;
    __chk_user_ptr(ptr);
    if (size > sizeof(x))
    (x) = __get_user_bad();

    Which doesn't immediately make sense because the size of the
    destination is u64, but it's not really, because __get_user_check()
    etc. internally create an unsigned long and copy into that:

    #define __get_user_check(x, ptr, size)
    ({
    long __gu_err = -EFAULT;
    unsigned long __gu_val = 0;

    The problem being that on 32-bit unsigned long is not big enough to
    hold a u64. We can fix this with a trick from hpa in the x86 code, we
    statically check the type of x and set the type of __gu_val to either
    unsigned long or unsigned long long.

    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/powerpc/include/asm/uaccess.h | 13 ++++++++++---
    1 file changed, 10 insertions(+), 3 deletions(-)

    --- a/arch/powerpc/include/asm/uaccess.h
    +++ b/arch/powerpc/include/asm/uaccess.h
    @@ -223,10 +223,17 @@ do { \
    } \
    } while (0)

    +/*
    + * This is a type: either unsigned long, if the argument fits into
    + * that type, or otherwise unsigned long long.
    + */
    +#define __long_type(x) \
    + __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
    +
    #define __get_user_nocheck(x, ptr, size) \
    ({ \
    long __gu_err; \
    - unsigned long __gu_val; \
    + __long_type(*(ptr)) __gu_val; \
    const __typeof__(*(ptr)) __user *__gu_addr = (ptr); \
    __chk_user_ptr(ptr); \
    if (!is_kernel_addr((unsigned long)__gu_addr)) \
    @@ -239,7 +246,7 @@ do { \
    #define __get_user_check(x, ptr, size) \
    ({ \
    long __gu_err = -EFAULT; \
    - unsigned long __gu_val = 0; \
    + __long_type(*(ptr)) __gu_val = 0; \
    const __typeof__(*(ptr)) __user *__gu_addr = (ptr); \
    might_fault(); \
    if (access_ok(VERIFY_READ, __gu_addr, (size))) \
    @@ -251,7 +258,7 @@ do { \
    #define __get_user_nosleep(x, ptr, size) \
    ({ \
    long __gu_err; \
    - unsigned long __gu_val; \
    + __long_type(*(ptr)) __gu_val; \
    const __typeof__(*(ptr)) __user *__gu_addr = (ptr); \
    __chk_user_ptr(ptr); \
    __get_user_size(__gu_val, __gu_addr, (size), __gu_err); \

    \
     
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