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    Subject[tip:x86/asm] syscalls/core: Prepare CONFIG_ARCH_HAS_SYSCALL_WRAPPER=y for compat syscalls
    Commit-ID:  7303e30ec1d8fb5ca1f07c92d069241c32b2ee1b
    Gitweb: https://git.kernel.org/tip/7303e30ec1d8fb5ca1f07c92d069241c32b2ee1b
    Author: Dominik Brodowski <linux@dominikbrodowski.net>
    AuthorDate: Thu, 5 Apr 2018 11:53:03 +0200
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Thu, 5 Apr 2018 16:59:38 +0200

    syscalls/core: Prepare CONFIG_ARCH_HAS_SYSCALL_WRAPPER=y for compat syscalls

    It may be useful for an architecture to override the definitions of the
    COMPAT_SYSCALL_DEFINE0() and __COMPAT_SYSCALL_DEFINEx() macros in
    <linux/compat.h>, in particular to use a different calling convention
    for syscalls. This patch provides a mechanism to do so, based on the
    previously introduced CONFIG_ARCH_HAS_SYSCALL_WRAPPER. If it is enabled,
    <asm/sycall_wrapper.h> is included in <linux/compat.h> and may be used
    to define the macros mentioned above. Moreover, as the syscall calling
    convention may be different if CONFIG_ARCH_HAS_SYSCALL_WRAPPER is set,
    the compat syscall function prototypes in <linux/compat.h> are #ifndef'd
    out in that case.

    As some of the syscalls and/or compat syscalls may not be present,
    the COND_SYSCALL() and COND_SYSCALL_COMPAT() macros in kernel/sys_ni.c
    as well as the SYS_NI() and COMPAT_SYS_NI() macros in
    kernel/time/posix-stubs.c can be re-defined in <asm/syscall_wrapper.h> iff
    CONFIG_ARCH_HAS_SYSCALL_WRAPPER is enabled.

    Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
    Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Link: http://lkml.kernel.org/r/20180405095307.3730-5-linux@dominikbrodowski.net
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    include/linux/compat.h | 22 ++++++++++++++++++++++
    init/Kconfig | 9 ++++++---
    kernel/sys_ni.c | 10 ++++++++++
    kernel/time/posix-stubs.c | 10 ++++++++++
    4 files changed, 48 insertions(+), 3 deletions(-)

    diff --git a/include/linux/compat.h b/include/linux/compat.h
    index 9847c5a013c3..2d85ec5cfda2 100644
    --- a/include/linux/compat.h
    +++ b/include/linux/compat.h
    @@ -24,6 +24,17 @@
    #include <asm/siginfo.h>
    #include <asm/signal.h>

    +#ifdef CONFIG_ARCH_HAS_SYSCALL_WRAPPER
    +/*
    + * It may be useful for an architecture to override the definitions of the
    + * COMPAT_SYSCALL_DEFINE0 and COMPAT_SYSCALL_DEFINEx() macros, in particular
    + * to use a different calling convention for syscalls. To allow for that,
    + + the prototypes for the compat_sys_*() functions below will *not* be included
    + * if CONFIG_ARCH_HAS_SYSCALL_WRAPPER is enabled.
    + */
    +#include <asm/syscall_wrapper.h>
    +#endif /* CONFIG_ARCH_HAS_SYSCALL_WRAPPER */
    +
    #ifndef COMPAT_USE_64BIT_TIME
    #define COMPAT_USE_64BIT_TIME 0
    #endif
    @@ -32,10 +43,12 @@
    #define __SC_DELOUSE(t,v) ((__force t)(unsigned long)(v))
    #endif

    +#ifndef COMPAT_SYSCALL_DEFINE0
    #define COMPAT_SYSCALL_DEFINE0(name) \
    asmlinkage long compat_sys_##name(void); \
    ALLOW_ERROR_INJECTION(compat_sys_##name, ERRNO); \
    asmlinkage long compat_sys_##name(void)
    +#endif /* COMPAT_SYSCALL_DEFINE0 */

    #define COMPAT_SYSCALL_DEFINE1(name, ...) \
    COMPAT_SYSCALL_DEFINEx(1, _##name, __VA_ARGS__)
    @@ -50,6 +63,7 @@
    #define COMPAT_SYSCALL_DEFINE6(name, ...) \
    COMPAT_SYSCALL_DEFINEx(6, _##name, __VA_ARGS__)

    +#ifndef COMPAT_SYSCALL_DEFINEx
    #define COMPAT_SYSCALL_DEFINEx(x, name, ...) \
    asmlinkage long compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__));\
    asmlinkage long compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))\
    @@ -62,6 +76,7 @@
    return C_SYSC##name(__MAP(x,__SC_DELOUSE,__VA_ARGS__)); \
    } \
    static inline long C_SYSC##name(__MAP(x,__SC_DECL,__VA_ARGS__))
    +#endif /* COMPAT_SYSCALL_DEFINEx */

    #ifndef compat_user_stack_pointer
    #define compat_user_stack_pointer() current_user_stack_pointer()
    @@ -517,7 +532,12 @@ int __compat_save_altstack(compat_stack_t __user *, unsigned long);
    * Please note that these prototypes here are only provided for information
    * purposes, for static analysis, and for linking from the syscall table.
    * These functions should not be called elsewhere from kernel code.
    + *
    + * As the syscall calling convention may be different from the default
    + * for architectures overriding the syscall calling convention, do not
    + * include the prototypes if CONFIG_ARCH_HAS_SYSCALL_WRAPPER is enabled.
    */
    +#ifndef CONFIG_ARCH_HAS_SYSCALL_WRAPPER
    asmlinkage long compat_sys_io_setup(unsigned nr_reqs, u32 __user *ctx32p);
    asmlinkage long compat_sys_io_submit(compat_aio_context_t ctx_id, int nr,
    u32 __user *iocb);
    @@ -955,6 +975,8 @@ asmlinkage long compat_sys_stime(compat_time_t __user *tptr);
    /* obsolete: net/socket.c */
    asmlinkage long compat_sys_socketcall(int call, u32 __user *args);

    +#endif /* CONFIG_ARCH_HAS_SYSCALL_WRAPPER */
    +

    /*
    * For most but not all architectures, "am I in a compat syscall?" and
    diff --git a/init/Kconfig b/init/Kconfig
    index 068eb6c3bbf7..2dbc88051bde 100644
    --- a/init/Kconfig
    +++ b/init/Kconfig
    @@ -1925,8 +1925,11 @@ config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
    bool

    # It may be useful for an architecture to override the definitions of the
    -# SYSCALL_DEFINE() and __SYSCALL_DEFINEx() macros in <linux/syscalls.h>,
    -# in particular to use a different calling convention for syscalls.
    +# SYSCALL_DEFINE() and __SYSCALL_DEFINEx() macros in <linux/syscalls.h>
    +# and the COMPAT_ variants in <linux/compat.h>, in particular to use a
    +# different calling convention for syscalls. They can also override the
    +# macros for not-implemented syscalls in kernel/sys_ni.c and
    +# kernel/time/posix-stubs.c. All these overrides need to be available in
    +# <asm/syscall_wrapper.h>.
    config ARCH_HAS_SYSCALL_WRAPPER
    def_bool n
    - depends on !COMPAT
    diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
    index 6cafc008f6db..9791364925dc 100644
    --- a/kernel/sys_ni.c
    +++ b/kernel/sys_ni.c
    @@ -5,6 +5,11 @@

    #include <asm/unistd.h>

    +#ifdef CONFIG_ARCH_HAS_SYSCALL_WRAPPER
    +/* Architectures may override COND_SYSCALL and COND_SYSCALL_COMPAT */
    +#include <asm/syscall_wrapper.h>
    +#endif /* CONFIG_ARCH_HAS_SYSCALL_WRAPPER */
    +
    /* we can't #include <linux/syscalls.h> here,
    but tell gcc to not warn with -Wmissing-prototypes */
    asmlinkage long sys_ni_syscall(void);
    @@ -17,8 +22,13 @@ asmlinkage long sys_ni_syscall(void)
    return -ENOSYS;
    }

    +#ifndef COND_SYSCALL
    #define COND_SYSCALL(name) cond_syscall(sys_##name)
    +#endif /* COND_SYSCALL */
    +
    +#ifndef COND_SYSCALL_COMPAT
    #define COND_SYSCALL_COMPAT(name) cond_syscall(compat_sys_##name)
    +#endif /* COND_SYSCALL_COMPAT */

    /*
    * This list is kept in the same order as include/uapi/asm-generic/unistd.h.
    diff --git a/kernel/time/posix-stubs.c b/kernel/time/posix-stubs.c
    index b258bee13b02..69a937c3cd81 100644
    --- a/kernel/time/posix-stubs.c
    +++ b/kernel/time/posix-stubs.c
    @@ -19,6 +19,11 @@
    #include <linux/posix-timers.h>
    #include <linux/compat.h>

    +#ifdef CONFIG_ARCH_HAS_SYSCALL_WRAPPER
    +/* Architectures may override SYS_NI and COMPAT_SYS_NI */
    +#include <asm/syscall_wrapper.h>
    +#endif
    +
    asmlinkage long sys_ni_posix_timers(void)
    {
    pr_err_once("process %d (%s) attempted a POSIX timer syscall "
    @@ -27,8 +32,13 @@ asmlinkage long sys_ni_posix_timers(void)
    return -ENOSYS;
    }

    +#ifndef SYS_NI
    #define SYS_NI(name) SYSCALL_ALIAS(sys_##name, sys_ni_posix_timers)
    +#endif
    +
    +#ifndef COMPAT_SYS_NI
    #define COMPAT_SYS_NI(name) SYSCALL_ALIAS(compat_sys_##name, sys_ni_posix_timers)
    +#endif

    SYS_NI(timer_create);
    SYS_NI(timer_gettime);
    \
     
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