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    Subject[PATCH] ARM: fix __get_user_check() in case uaccess_* calls are not inlined
    Date
    KernelCI reports that bcm2835_defconfig is no longer booting since
    commit ac7c3e4ff401 ("compiler: enable CONFIG_OPTIMIZE_INLINING
    forcibly"):

    https://lkml.org/lkml/2019/9/26/825

    I also received a regression report from Nicolas Saenz Julienne:

    https://lkml.org/lkml/2019/9/27/263

    This problem has cropped up on arch/arm/config/bcm2835_defconfig
    because it enables CONFIG_CC_OPTIMIZE_FOR_SIZE. The compiler tends
    to prefer not inlining functions with -Os. I was able to reproduce
    it with other boards and defconfig files by manually enabling
    CONFIG_CC_OPTIMIZE_FOR_SIZE.

    The __get_user_check() specifically uses r0, r1, r2 registers.
    So, uaccess_save_and_enable() and uaccess_restore() must be inlined
    in order to avoid those registers being overwritten in the callees.

    Prior to commit 9012d011660e ("compiler: allow all arches to enable
    CONFIG_OPTIMIZE_INLINING"), the 'inline' marker was always enough for
    inlining functions, except on x86.

    Since that commit, all architectures can enable CONFIG_OPTIMIZE_INLINING.
    So, __always_inline is now the only guaranteed way of forcible inlining.

    I want to keep as much compiler's freedom as possible about the inlining
    decision. So, I changed the function call order instead of adding
    __always_inline around.

    Call uaccess_save_and_enable() before assigning the __p ("r0"), and
    uaccess_restore() after evacuating the __e ("r0").

    Fixes: 9012d011660e ("compiler: allow all arches to enable CONFIG_OPTIMIZE_INLINING")
    Reported-by: "kernelci.org bot" <bot@kernelci.org>
    Reported-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
    Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
    ---

    arch/arm/include/asm/uaccess.h | 8 +++++---
    1 file changed, 5 insertions(+), 3 deletions(-)

    diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
    index 303248e5b990..559f252d7e3c 100644
    --- a/arch/arm/include/asm/uaccess.h
    +++ b/arch/arm/include/asm/uaccess.h
    @@ -191,11 +191,12 @@ extern int __get_user_64t_4(void *);
    #define __get_user_check(x, p) \
    ({ \
    unsigned long __limit = current_thread_info()->addr_limit - 1; \
    + unsigned int __ua_flags = uaccess_save_and_enable(); \
    register typeof(*(p)) __user *__p asm("r0") = (p); \
    register __inttype(x) __r2 asm("r2"); \
    register unsigned long __l asm("r1") = __limit; \
    register int __e asm("r0"); \
    - unsigned int __ua_flags = uaccess_save_and_enable(); \
    + unsigned int __err; \
    switch (sizeof(*(__p))) { \
    case 1: \
    if (sizeof((x)) >= 8) \
    @@ -223,9 +224,10 @@ extern int __get_user_64t_4(void *);
    break; \
    default: __e = __get_user_bad(); break; \
    } \
    - uaccess_restore(__ua_flags); \
    + __err = __e; \
    x = (typeof(*(p))) __r2; \
    - __e; \
    + uaccess_restore(__ua_flags); \
    + __err; \
    })

    #define get_user(x, p) \
    --
    2.17.1
    \
     
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